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      How To Create an HTTP Client with Core HTTP in Node.js


      The author selected the COVID-19 Relief Fund to receive a donation as part of the Write for DOnations program.

      Introduction

      It’s common for a modern web application to communicate with other servers to accomplish a task. For example, a web app that allows you to purchase a book online may involve communication between a customer orders server, a book inventory server, and a payment server. In this design, the different services communicate via web APIs—standard formats that allow you to programmatically send and receive data. In a Node.js app, you can communicate with web APIs by making HTTP requests.

      Node.js comes bundled with an http and an https module. These modules have functions to create an HTTP server so that a Node.js program can respond to HTTP requests. They can also make HTTP requests to other servers. This key functionality equips Node.js programmers to create modern, API-driven web applications with Node.js. As it’s a core module, you do not need to install any libraries to use it.

      In this tutorial, you will use the https module to make HTTP requests to JSON Placeholder, a fake REST API for testing purposes. You will begin by making a GET request, the standard HTTP request to receive data. You will then look at ways to customize your request, such as by adding headers. Finally, you will make POST, PUT, and DELETE requests so that you can modify data in an external server.

      Prerequisites

      • This tutorial requires that you have Node.js installed. Once installed, you will be able to access the https module that’s used throughout the tutorial. This tutorial uses Node.js version 10.19.0. To install Node.js on macOS or Ubuntu 18.04, follow the steps in How To Install Node.js and Create a Local Development Environment on macOS or the Installing Using a PPA section of How To Install Node.js on Ubuntu 18.04.

      • The methods used to send HTTP requests have a Stream-based API. In Node.js, streams are instances of event emitters. The way in which you respond to data coming from a stream is the same as the way in which you respond to data from events. If you are curious, you can get more in-depth knowledge of event emitters by reading our Using Event Emitters in Node.js guide.

      Step 1 — Making a GET Request

      When you interact with an API, you typically make GET requests to retrieve data from web servers. In this step, you’ll look at two functions to make GET requests in Node.js. Your code will retrieve a JSON array of user profiles from a publicly accessible API.

      The https module has two functions to make GET requests—the get() function, which can only make GET requests, and the request() function, which makes other types of requests. You will begin by making a request with the get() function.

      Making Requests with get()

      HTTP requests using the get() function have this format:

      https.get(URL_String, Callback_Function) {
          Action
      }
      

      The first argument is a string with the endpoint you’re making the request to. The second argument is a callback function, which you use to handle the response.

      First, set up your coding environment. In your terminal, create a folder to store all your Node.js modules for this guide:

      Enter that folder:

      Create and open a new file in a text editor. This tutorial will use nano as it’s available in the terminal:

      • nano getRequestWithGet.js

      To make HTTP requests in Node.js, import the https module by adding the follow line:

      requests/getRequestWithGet.js

      const https = require('https');
      

      Note:: Node.js has an http and an https module. They have the same functions and behave in a similar manner, but https makes the requests through the Transport Layer Security (TLS/SSL). As the web servers you are using are available via HTTPS, you will use the https module. If you are making requests to and from URLs that only have HTTP, then you would use the http module.

      Now use the http object to make a GET request to the API to retrieve a list of users. You will use JSON Placeholder, a publicly available API for testing. This API does not keep a record of any changes you make in your requests. It simulates a real server, and returns mocked responses as long as you send a valid request.

      Write the following highlighted code in your text editor:

      requests/getRequestWithGet.js

      const https = require('https');
      
      let request = https.get('https://jsonplaceholder.typicode.com/users?_limit=2', (res) => { });
      

      As mentioned in the function signature, the get() function takes two parameters. The first is the API URL you are making the request to in string format and the second is a callback to handle the HTTP response. To read the data from your response, you have to add some code in the callback.

      HTTP responses come with a status code. A status code is a number that indicates how successful the response was. Status codes between 200 and 299 are positive responses, while codes between 400 and 599 are errors. You can learn more about status codes in our How To Troubleshoot Common HTTP Error Codes guide.

      For this request, a successful response would have a 200 status code. The first thing you’ll do in your callback will be to verify that the status code is what you expect. Add the following code to the callback function:

      requests/getRequestWithGet.js

      const https = require('https');
      
      let request = https.get('https://jsonplaceholder.typicode.com/users?_limit=2', (res) => {
        if (res.statusCode !== 200) {
          console.error(`Did not get an OK from the server. Code: ${res.statusCode}`);
          res.resume();
          return;
        }
      });
      

      The response object that’s available in the callback has a statusCode property that stores the status code. If the status code is not 200, you log an error to the console and exit.

      Note the line that has res.resume(). You included that line to improve performance. When making HTTP requests, Node.js will consume all the data that’s sent with the request. The res.resume() method tells Node.js to ignore the stream’s data. In turn, Node.js would typically discard the data more quickly than if it left it for garbage collection—a periodic process that frees an application’s memory.

      Now that you’ve captured error responses, add code to read the data. Node.js responses stream their data in chunks. The strategy for retrieving data will be to listen for when data comes from the response, collate all the chunks, and then parse the JSON so your application can use it.

      Modify the request callback to include this code:

      requests/getRequestWithGet.js

      const https = require('https');
      
      let request = https.get('https://jsonplaceholder.typicode.com/users?_limit=2', (res) => {
        if (res.statusCode !== 200) {
          console.error(`Did not get an OK from the server. Code: ${res.statusCode}`);
          res.resume();
          return;
        }
      
        let data="";
      
        res.on('data', (chunk) => {
          data += chunk;
        });
      
        res.on('close', () => {
          console.log('Retrieved all data');
          console.log(JSON.parse(data));
        });
      });
      

      You begin by creating a new variable data that’s an empty string. You can store data as an array of numbers representing byte data or a string. This tutorial uses the latter as it’s easier to convert a JSON string to a JavaScript object.

      After creating the data variable, you create an event listener. Node.js streams the data of an HTTP response in chunks. Therefore, when the response object emits a data event, you will take the data it received and add it to your data variable.

      When all the data from the server is received, Node.js emits a close event. At this point, you parse the JSON string stored in data and log the result to the console.

      Your Node.js module can now communicate with the JSON API and log the list of users, which will be a JSON array of three users. However, there’s one small improvement you can make first.

      This script will throw an error if you are unable to make a request. You may not be able to make a request if you lose your internet connection, for example. Add the following code to capture errors when you’re unable to send an HTTP request:

      requests/getRequestWithGet.js

      ...
        res.on('data', (chunk) => {
          data += chunk;
        });
      
        res.on('close', () => {
          console.log('Retrieved all data');
          console.log(JSON.parse(data));
        });
      
      });
      
      request.on('error', (err) => {
        console.error(`Encountered an error trying to make a request: ${err.message}`);
      });
      

      When a request is made but cannot be sent, the request object emits an error event. If an error event is emitted but not listened to, the Node.js program crashes. Therefore, to capture errors you add an event listener with the on() function and listen for error events. When you get an error, you log its message.

      That’s all the code for this file. Save and exit nano by pressing CTRL+X.

      Now execute this program with node:

      • node getRequestWithGet.js

      Your console will display this response:

      Output

      Retrieved all data [ { id: 1, name: 'Leanne Graham', username: 'Bret', email: 'Sincere@april.biz', address: { street: 'Kulas Light', suite: 'Apt. 556', city: 'Gwenborough', zipcode: '92998-3874', geo: [Object] }, phone: '1-770-736-8031 x56442', website: 'hildegard.org', company: { name: 'Romaguera-Crona', catchPhrase: 'Multi-layered client-server neural-net', bs: 'harness real-time e-markets' } }, { id: 2, name: 'Ervin Howell', username: 'Antonette', email: 'Shanna@melissa.tv', address: { street: 'Victor Plains', suite: 'Suite 879', city: 'Wisokyburgh', zipcode: '90566-7771', geo: [Object] }, phone: '010-692-6593 x09125', website: 'anastasia.net', company: { name: 'Deckow-Crist', catchPhrase: 'Proactive didactic contingency', bs: 'synergize scalable supply-chains' } } ]

      This means you’ve successfully made a GET request with the core Node.js library.

      The get() method you used is a convenient method Node.js provides because GET requests are a very common type of request. Node.js provides a request() method to make a request of any type. Next, this tutorial will examine how to make a GET request with request().

      Making Requests with request()

      The request() method supports multiple function signatures. You’ll use this one for the subsequent example:

      https.request(URL_String, Options_Object, Callback_Function) {
          Action
      }
      

      The first argument is a string with the API endpoint. The second argument is a JavaScript object containing all the options for the request. The last argument is a callback function to handle the response.

      Create a new file for a new module called getRequestWithRequest.js:

      • nano getRequestWithRequest.js

      The code you will write is similar to the getRequestWithGet.js module you wrote earlier. First, import the https module:

      requests/getRequestWithRequest.js

      const https = require('https');
      

      Next, create a new JavaScript object that contains a method key:

      requests/getRequestWithRequest.js

      const https = require('https');
      
      const options = {
        method: 'GET'
      };
      

      The method key in this object will tell the request() function what HTTP method the request is using.

      Next, make the request in your code. The following codeblock highlights code that was different from the request made with the get() method. In your editor, enter all of the following lines:

      requests/getRequestWithRequest.js

      ...
      
      let request = https.request('https://jsonplaceholder.typicode.com/users?_limit=2', options, (res) => {
        if (res.statusCode !== 200) {
          console.error(`Did not get an OK from the server. Code: ${res.statusCode}`);
          res.resume();
          return;
        }
      
        let data="";
      
        res.on('data', (chunk) => {
          data += chunk;
        });
      
        res.on('close', () => {
          console.log('Retrieved all data');
          console.log(JSON.parse(data));
        });
      });
      
      request.end();
      
      request.on('error', (err) => {
        console.error(`Encountered an error trying to make a request: ${err.message}`);
      });
      

      To make a request using request(), you provide the URL in the first argument, an object with the HTTP options in the second argument, and a callback to handle the response in the third argument.

      The options variable you created earlier is the second argument, telling Node.js that this is a GET request. The callback is unchanged from when you first wrote it.

      You also call the end() method of the request variable. This is an important method that must be called when using the request() function. It completes the request, allowing it to be sent. If you don’t call it, the program will never complete, as Node.js will think you still have data to add to the request.

      Save and exit nano with CTRL+X, or the equivalent with your text editor.

      Run this program in your terminal:

      • node getRequestWithRequest.js

      You will receive this output, which is the same as the first module:

      Output

      Retrieved all data [ { id: 1, name: 'Leanne Graham', username: 'Bret', email: 'Sincere@april.biz', address: { street: 'Kulas Light', suite: 'Apt. 556', city: 'Gwenborough', zipcode: '92998-3874', geo: [Object] }, phone: '1-770-736-8031 x56442', website: 'hildegard.org', company: { name: 'Romaguera-Crona', catchPhrase: 'Multi-layered client-server neural-net', bs: 'harness real-time e-markets' } }, { id: 2, name: 'Ervin Howell', username: 'Antonette', email: 'Shanna@melissa.tv', address: { street: 'Victor Plains', suite: 'Suite 879', city: 'Wisokyburgh', zipcode: '90566-7771', geo: [Object] }, phone: '010-692-6593 x09125', website: 'anastasia.net', company: { name: 'Deckow-Crist', catchPhrase: 'Proactive didactic contingency', bs: 'synergize scalable supply-chains' } } ]

      You have now used the request() method to make a GET request. It’s important to know this function as it allows you to customize your request in ways the get() method cannot, like making requests with other HTTP methods.

      Next, you will configure and customize your requests with the request() function.

      Step 2 — Configuring HTTP request() Options

      The request() function allows you to send HTTP requests without specifying the URL in the first argument. In this case, the URL would be contained with the options object, and the request() would have this function signature:

      https.request(Options_Object, Callback_Function) {
          Action
      }
      

      In this step, you will use this functionality to configure your request() with the options object.

      Node.js allows you to enter the URL in the options object you pass to the request. To try this out, reopen the getRequestWithRequest.js file:

      • nano getRequestWithRequest.js

      Remove the URL from the request() call so that the only arguments are the options variable and the callback function:

      requests/getRequestWithRequest.js

      const https = require('https');
      
      const options = {
        method: 'GET',
      };
      
      let request = https.request(options, (res) => {
      ...
      

      Now add the following properties to the options object:

      requests/getRequestWithRequest.js

      const https = require('https');
      
      const options = {
        host: 'jsonplaceholder.typicode.com',
        path: '/users?_limit=2',
        method: 'GET'
      };
      
      let request = https.request(options, (res) => {
      ...
      

      Instead of one string URL, you have two properties—host and path. The host is the domain name or IP address of the server you’re accessing. The path is everything that comes after the domain name, including query parameters (values after the question mark).

      The options object can hold other useful data that goes into a request. For example, you can provide request headers in the options. Headers typically send metadata about the request.

      When developers create APIs, they may choose to support different data formats. One API endpoint may be able to return data in JSON, CSV, or XML. In those APIs, the server may look at the Accept header to determine the correct response type.

      The Accept header specifies the type of data the user can handle. While the API being used in these examples only return JSON, you can add the Accept header to your request to explicitly state that you want JSON.

      Add the following lines of code to append the Accept header:

      requests/getRequestWithRequest.js

      const https = require('https');
      
      const options = {
        host: 'jsonplaceholder.typicode.com',
        path: '/users?_limit=2',
        method: 'GET',
        headers: {
          'Accept': 'application/json'
        }
      };
      

      By adding headers, you’ve covered the four most popular options that are sent in Node.js HTTP requests: host, path, method, and headers. Node.js supports many more options; you can read more at the official Node.js docs for more information.

      Enter CTRL+X to save your file and exit nano.

      Next, run your code once more to make the request by only using options:

      • node getRequestWithRequest.js

      The results will be the same as your previous runs:

      Output

      Retrieved all data [ { id: 1, name: 'Leanne Graham', username: 'Bret', email: 'Sincere@april.biz', address: { street: 'Kulas Light', suite: 'Apt. 556', city: 'Gwenborough', zipcode: '92998-3874', geo: [Object] }, phone: '1-770-736-8031 x56442', website: 'hildegard.org', company: { name: 'Romaguera-Crona', catchPhrase: 'Multi-layered client-server neural-net', bs: 'harness real-time e-markets' } }, { id: 2, name: 'Ervin Howell', username: 'Antonette', email: 'Shanna@melissa.tv', address: { street: 'Victor Plains', suite: 'Suite 879', city: 'Wisokyburgh', zipcode: '90566-7771', geo: [Object] }, phone: '010-692-6593 x09125', website: 'anastasia.net', company: { name: 'Deckow-Crist', catchPhrase: 'Proactive didactic contingency', bs: 'synergize scalable supply-chains' } } ]

      As APIs can vary from provider to provider, being comfortable with the options object is key to adapting to their differing requirements, with the data types and headers being some of the most common variations.

      So far, you have only done GET requests to retrieve data. Next, you will make a POST request with Node.js so you can upload data to a server.

      Step 3 — Making a POST Request

      When you upload data to a server or want the server to create data for you, you typically send a POST request. In this section, you’ll create a POST request in Node.js. You will make a request to create a new user in the users API.

      Despite being a different method from GET, you will be able to reuse code from the previous requests when writing your POST request. However, you will have to make the following adjustments:

      • Change the method in the options object to POST
      • Add a header to state you are uploading JSON
      • Check the status code to confirm a user was created
      • Upload the new user’s data

      To make these changes, first create a new file called postRequest.js. Open this file in nano or an alternative text editor:

      Begin by importing the https module and creating an options object:

      requests/postRequest.js

      const https = require('https');
      
      const options = {
        host: 'jsonplaceholder.typicode.com',
        path: '/users',
        method: 'POST',
        headers: {
          'Accept': 'application/json',
          'Content-Type': 'application/json; charset=UTF-8'
        }
      };
      

      You change the path to match what’s required for POST requests. You also updated the method to POST. Lastly, you added a new header in your options Content-Type. This header tells the server what type of data you are uploading. In this case, you’ll be uploading JSON data with UTF-8 encoding.

      Next, make the request with the request() function. This is similar to how you made GET requests, but now you look for a different status code than 200. Add the following lines to the end of your code:

      requests/postRequest.js

      ...
      const request = https.request(options, (res) => {
        if (res.statusCode !== 201) {
          console.error(`Did not get a Created from the server. Code: ${res.statusCode}`);
          res.resume();
          return;
        }
      
        let data="";
      
        res.on('data', (chunk) => {
          data += chunk;
        });
      
        res.on('close', () => {
          console.log('Added new user');
          console.log(JSON.parse(data));
        });
      });
      

      The highlighted line of code checks if the status code is 201. The 201 status code is used to indicate that the server created a resource.

      This POST request is meant to create a new user. For this API, you need to upload the user details. Create some user data and send that with your POST request:

      requests/postRequest.js

      ...
      
      const requestData = {
        name: 'New User',
        username: 'digitalocean',
        email: 'user@digitalocean.com',
        address: {
          street: 'North Pole',
          city: 'Murmansk',
          zipcode: '12345-6789',
        },
        phone: '555-1212',
        website: 'digitalocean.com',
        company: {
          name: 'DigitalOcean',
          catchPhrase: 'Welcome to the developer cloud',
          bs: 'cloud scale security'
        }
      };
      
      request.write(JSON.stringify(requestData));
      

      You first created the requestData variable, which is a JavaScript object containing user data. Your request does not include an id field, as servers typically generate these while saving the new data.

      You next use the request.write() function, which accepts a string or buffer object to send along with the request. As your requestData variable is an object, you used the JSON.stringify function to convert it to a string.

      To complete this module, end the request and check for errors:

      requests/postRequest.js

      ...
      
      request.end();
      
      request.on('error', (err) => {
        console.error(`Encountered an error trying to make a request: ${err.message}`);
      });
      

      It’s important that you write data before you use the end() function. The end() function tells Node.js that there’s no more data to be added to the request and sends it.

      Save and exit nano by pressing CTRL+X.

      Run this program to confirm that a new user was created:

      The following output will be displayed:

      Output

      Added new user { name: 'New User', username: 'digitalocean', email: 'user@digitalocean.com', address: { street: 'North Pole', city: 'Murmansk', zipcode: '12345-6789' }, phone: '555-1212', website: 'digitalocean.com', company: { name: 'DigitalOcean', catchPhrase: 'Welcome to the developer cloud', bs: 'cloud scale security' }, id: 11 }

      The output confirms that the request was successful. The API returned the user data that was uploaded, along with the ID that was assigned to it.

      Now that you have learned how to make POST requests, you can upload data to servers in Node.js. Next you will try out PUT requests, a method used to update data in a server.

      Step 4 — Making a PUT Request

      Developers make a PUT request to upload data to a server. While this may be similar to POST requests, PUT requests have a different function. PUT requests are idempotent—you can run a PUT request multiple times and it will have the same result.

      In practice, the code you write is similar to that of a POST request. You set up your options, make your request, write the data you want to upload, and verify the response.

      To try this out, you’re going to create a PUT request that updates the first user’s username.

      As the code is similar to the POST request, you’ll use that module as a base for this one. Copy the postRequest.js into a new file, putRequest.js:

      • cp postRequest.js putRequest.js

      Now open putRequest.js in a text editor:

      Make these highlighted changes so that you send a PUT request to https://jsonplaceholder.typicode.com/users/1:

      requests/putRequest.js

      const https = require('https');
      
      const options = {
        host: 'jsonplaceholder.typicode.com',
        path: '/users/1',
        method: 'PUT',
        headers: {
          'Accept': 'application/json',
          'Content-Type': 'application/json; charset=UTF-8'
        }
      };
      
      const request = https.request(options, (res) => {
        if (res.statusCode !== 200) {
          console.error(`Did not get an OK from the server. Code: ${res.statusCode}`);
          res.resume();
          return;
        }
      
        let data="";
      
        res.on('data', (chunk) => {
          data += chunk;
        });
      
        res.on('close', () => {
          console.log('Updated data');
          console.log(JSON.parse(data));
        });
      });
      
      const requestData = {
        username: 'digitalocean'
      };
      
      request.write(JSON.stringify(requestData));
      
      request.end();
      
      request.on('error', (err) => {
        console.error(`Encountered an error trying to make a request: ${err.message}`);
      });
      

      You first change the path and method properties of the options object. path in this case identifies the user that you are going to update. When you make the request, you check if the response code was 200, meaning that the request was OK. The data you are uploading now only contains the property you are updating.

      Save and exit nano with CTRL+X.

      Now execute this Node.js program in your terminal:

      You will receive this output:

      Output

      Updated data { username: 'digitalocean', id: 1 }

      You sent a PUT request to update a pre-existing user.

      So far you have learned how to retrieve, add, and update data. To give us a full command of managing data via APIs, you’ll next make a DELETE request to remove data from a server.

      Step 5 — Making a DELETE Request

      The DELETE request is used to remove data from a server. It can have a request body, but most APIs tend not to require them. This method is used to delete an entire object from the server. In this section, you are going to delete a user using the API.

      The code you will write is similar to that of a GET request, so use that module as a base for this one. Copy the getRequestWithRequest.js file into a new deleteRequest.js file:

      • cp getRequestWithRequest.js deleteRequest.js

      Open deleteRequest.js with nano:

      Now modify the code at the highlighted parts, so you can delete the first user in the API:

      requests/putRequest.js

      const https = require('https');
      
      const options = {
        host: 'jsonplaceholder.typicode.com',
        path: '/users/1',
        method: 'DELETE',
        headers: {
          'Accept': 'application/json',
        }
      };
      
      const request = https.request(options, (res) => {
        if (res.statusCode !== 200) {
          console.error(`Did not get an OK from the server. Code: ${res.statusCode}`);
          res.resume();
          return;
        }
      
        let data="";
      
        res.on('data', (chunk) => {
          data += chunk;
        });
      
        res.on('close', () => {
          console.log('Deleted user');
          console.log(JSON.parse(data));
        });
      });
      
      request.end();
      
      request.on('error', (err) => {
        console.error(`Encountered an error trying to make a request: ${err.message}`);
      });
      

      For this module, you begin by changing the path property of the options object to the resource you want to delete—the first user. You then change the method to DELETE.

      Save and exit this file by pressing CTRL+X.

      Run this module to confirm it works. Enter the following command in your terminal:

      The program will output this:

      Output

      Deleted user {}

      While the API does not return a response body, you still got a 200 response so the request was OK.

      You’ve now learned how to make DELETE requests with Node.js core modules.

      Conclusion

      In this tutorial, you made GET, POST, PUT, and DELETE requests in Node.js. No libraries were installed; these requests were made using the standard https module. While GET requests can be made with a get() function, all other HTTP methods are done via the request() method.

      The code you wrote was written for a publicly available, test API. However, the way you write requests will work for all types of APIs. If you would like to learn more about APIs, check out our API topic page. For more on developing in Node.js, return to the How To Code in Node.js series.



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      Como Monitorar seu Banco de Dados PostgreSQL Gerenciado Usando o Nagios Core no Ubuntu 18.04


      O autor escolheu o Free and Open Source Fund para receber uma doação como parte do programa Write for DOnations.

      Introdução

      O monitoramento do banco de dados é essencial para entender como o banco de dados se comporta ao longo do tempo. Ele pode ajudá-lo a descobrir problemas de utilização ocultos e gargalos que ocorrem no seu banco de dados. A implementação de sistemas de monitoramento de banco de dados pode rapidamente se tornar uma vantagem a longo prazo, o que influenciará positivamente seu processo de gerenciamento de infraestrutura. Você poderá reagir rapidamente às alterações de status do seu banco de dados e será notificado rapidamente quando os serviços monitorados retornarem ao funcionamento normal.

      O Nagios Core é um sistema de monitoramento popular que você pode usar para monitorar seu banco de dados gerenciado. Os benefícios de usar o Nagios para esta tarefa são sua versatilidade — é fácil de configurar e utiliza um grande repositório de plugins disponíveis, e o mais importante, alerta integrado.

      Neste tutorial, você configurará o monitoramento do banco de dados PostgreSQL no Nagios Core utilizando o plugin check_postgres e configurar alertas baseados no Slack. No final, você terá um sistema de monitoramento funcionando em seu banco de dados PostgreSQL gerenciado e será notificado imediatamente sobre alterações de status de várias funcionalidades.

      Pré-requisitos

      Passo 1 — Instalando check_postgres

      Nesta seção, você fará o download da versão mais recente do plug-in check_postgres no Github e disponibilizará para o Nagios Core. Você também instalará o cliente PostgreSQL (psql), para que check_postgres consiga se conectar ao seu banco de dados gerenciado.

      Comece instalando o cliente PostgreSQL, executando o seguinte comando:

      • sudo apt install postgresql-client

      Em seguida, você baixará o check_postgres para o seu diretório home. Primeiro, navegue até ele:

      Vá para a página Github releases e copie o link da versão mais recente do plug-in. No momento da redação deste artigo, a versão mais recente do check_postgres era a 2.24.0; lembre-se de que isso será atualizado e, sempre que possível, a boa prática é usar a versão mais recente.

      Agora faça o download usando curl:

      • curl -LO https://github.com/bucardo/check_postgres/releases/download/2.24.0/check_postgres-2.24.0.tar.gz

      Extraia-o usando o seguinte comando:

      • tar xvf check_postgres-*.tar.gz

      Isso criará um diretório com o mesmo nome que o arquivo que você baixou. Essa pasta contém o executável check_postgres, que você precisará copiar para o diretório em que o Nagios armazena seus plugins (geralmente /usr/local/nagios/libexec/). Copie-o executando o seguinte comando:

      • sudo cp check_postgres-*/check_postgres.pl /usr/local/nagios/libexec/

      Em seguida, você precisará atribuir ao usuário nagios a propriedade sobre ele, para que ele possa ser executado a partir do Nagios:

      • sudo chown nagios:nagios /usr/local/nagios/libexec/check_postgres.pl

      O check_postgres está agora disponível para o Nagios e pode ser usado a partir dele. No entanto, ele fornece muitos comandos relativos a diferentes aspectos do PostgreSQL e, para uma melhor manutenção do serviço, é melhor dividi-los para que possam ser chamados separadamente. Você conseguirá isso criando um link simbólico para cada comando check_postgres no diretório do plugin.

      Navegue para o diretório onde o Nagios armazena plugins executando o seguinte comando:

      • cd /usr/local/nagios/libexec

      Em seguida, crie os links simbólicos com:

      • sudo perl check_postgres.pl --symlinks

      A saída será semelhante a esta:

      Output

      Created "check_postgres_archive_ready" Created "check_postgres_autovac_freeze" Created "check_postgres_backends" Created "check_postgres_bloat" Created "check_postgres_checkpoint" Created "check_postgres_cluster_id" Created "check_postgres_commitratio" Created "check_postgres_connection" Created "check_postgres_custom_query" Created "check_postgres_database_size" Created "check_postgres_dbstats" Created "check_postgres_disabled_triggers" Created "check_postgres_disk_space" Created "check_postgres_fsm_pages" Created "check_postgres_fsm_relations" Created "check_postgres_hitratio" Created "check_postgres_hot_standby_delay" Created "check_postgres_index_size" Created "check_postgres_indexes_size" Created "check_postgres_last_analyze" Created "check_postgres_last_autoanalyze" Created "check_postgres_last_autovacuum" Created "check_postgres_last_vacuum" Created "check_postgres_listener" Created "check_postgres_locks" Created "check_postgres_logfile" Created "check_postgres_new_version_bc" Created "check_postgres_new_version_box" Created "check_postgres_new_version_cp" Created "check_postgres_new_version_pg" Created "check_postgres_new_version_tnm" Created "check_postgres_pgagent_jobs" Created "check_postgres_pgb_pool_cl_active" Created "check_postgres_pgb_pool_cl_waiting" Created "check_postgres_pgb_pool_maxwait" Created "check_postgres_pgb_pool_sv_active" Created "check_postgres_pgb_pool_sv_idle" Created "check_postgres_pgb_pool_sv_login" Created "check_postgres_pgb_pool_sv_tested" Created "check_postgres_pgb_pool_sv_used" Created "check_postgres_pgbouncer_backends" Created "check_postgres_pgbouncer_checksum" Created "check_postgres_prepared_txns" Created "check_postgres_query_runtime" Created "check_postgres_query_time" Created "check_postgres_relation_size" Created "check_postgres_replicate_row" Created "check_postgres_replication_slots" Created "check_postgres_same_schema" Created "check_postgres_sequence" Created "check_postgres_settings_checksum" Created "check_postgres_slony_status" Created "check_postgres_table_size" Created "check_postgres_timesync" Created "check_postgres_total_relation_size" Created "check_postgres_txn_idle" Created "check_postgres_txn_time" Created "check_postgres_txn_wraparound" Created "check_postgres_version" Created "check_postgres_wal_files"

      O Perl listou todas as funções para as quais criou um link simbólico. Agora elas podem ser executadas na linha de comando, como de costume.

      Você baixou e instalou o plug-in check_postgres. Você também criou links simbólicos para todos os comandos do plug-in, para que possam ser usados individualmente no Nagios. No próximo passo, você criará um arquivo de serviço de conexão, que o check_postgres utilizará para se conectar ao seu banco de dados gerenciado.

      Passo 2 — Configurando Seu Banco de Dados

      Nesta seção, você criará um arquivo de serviço de conexão do PostgreSQL contendo as informações de conexão do seu banco de dados. A seguir, você testará os dados de conexão invocando o check_postgres nele.

      O arquivo do serviço de conexão é, por convenção, chamado pg_service.conf e deve estar localizado em /etc/postgresql-common/. Crie este arquivo usando seu editor de textos favorito (por exemplo, o nano):

      • sudo nano /etc/postgresql-common/pg_service.conf

      Adicione as seguintes linhas, substituindo os espaços reservados destacados pelos valores reais mostrados no Painel de Controle do Banco de Dados gerenciado na seção Connection Details:

      /etc/postgresql-common/pg_service.conf

      [managed-db]
      host=host
      port=porta
      user=nome_de_usuário
      password=senha
      dbname=defaultdb
      sslmode=require
      

      O arquivo do serviço de conexão pode abrigar vários grupos de informações de conexão com o banco de dados. O início de um grupo é sinalizado colocando seu nome entre colchetes. Depois disso vem os parâmetros de conexão (host, port, user, password e assim por diante), separados por novas linhas, que devem receber um valor.

      Salve e feche o arquivo quando terminar.

      Agora você testará a validade da configuração conectando-se ao banco de dados via check_postgres executando o seguinte comando:

      • ./check_postgres.pl --dbservice=managed-db --action=connection

      Aqui, você diz ao check_postgres qual grupo de informações de conexão com o banco de dados usar com o parâmetro --dbservice, e também especifica que ele deve apenas tentar se conectar a ele especificando connection como a ação.

      Sua saída será semelhante a esta:

      Output

      POSTGRES_CONNECTION OK: service=managed-db version 11.4 | time=0.10s

      Isto significa que o check_postgres conseguiu conectar-se ao banco de dados, de acordo com os parâmetros do pg_service.conf. Se você receber um erro, verifique novamente o que você acabou de inserir nesse arquivo de configuração.

      Você criou e preencheu um arquivo de serviço de conexão do PostgreSQL, que funciona como uma string de conexão. Você também testou os dados de conexão executando check_postgres e observando a saída. Na próxima etapa, você configurará o Nagios para monitorar várias partes do seu banco de dados.

      Passo 3 — Criando Serviços de Monitoramento no Nagios

      Agora você configurará o Nagios para monitorar várias métricas do seu banco de dados, definindo um host e vários serviços, que chamarão o plug-in check_postgres e seus links simbólicos.

      O Nagios armazena seus arquivos de configuração personalizados em /usr/local/nagios/etc/objects. Os novos arquivos adicionados lá devem ser ativados manualmente no arquivo de configuração central do Nagios, localizado em /usr/local/nagios/etc/nagios.cfg. Agora você deverá definir comandos, um host e vários serviços, que serão usados para monitorar seu banco de dados gerenciado no Nagios.

      Primeiro, crie uma pasta dentro de /usr/local/nagios/etc/objects para armazenar sua configuração relacionada ao PostgreSQL executando o seguinte comando:

      • sudo mkdir /usr/local/nagios/etc/objects/postgresql

      Você armazenará os comandos do Nagios para check_nagios em um arquivo chamado commands.cfg. Crie-o para edição:

      • sudo nano /usr/local/nagios/etc/objects/postgresql/commands.cfg

      Adicione as seguintes linhas:

      /usr/local/nagios/etc/objects/postgresql/commands.cfg

      define command {
          command_name           check_postgres_connection
          command_line           /usr/local/nagios/libexec/check_postgres_connection --dbservice=$ARG1$
      }
      
      define command {
          command_name           check_postgres_database_size
          command_line           /usr/local/nagios/libexec/check_postgres_database_size --dbservice=$ARG1$ --critical='$ARG2$'
      }
      
      define command {
          command_name           check_postgres_locks
          command_line           /usr/local/nagios/libexec/check_postgres_locks --dbservice=$ARG1$
      }
      
      define command {
          command_name           check_postgres_backends
          command_line           /usr/local/nagios/libexec/check_postgres_backends --dbservice=$ARG1$
      }
      

      Salve e feche o arquivo.

      Neste arquivo, você define quatro comandos do Nagios que chamam partes diferentes do plugin check_postgres (checando a conectividade, obtendo o número de locks e conexões e o tamanho de todo o banco de dados). Todos eles aceitam um argumento que é passado para o parâmetro --dbservice e especificam a qual dos bancos de dados definidos em pg_service.conf se conectar.

      O comando check_postgres_database_size aceita um segundo argumento que é passado para o parâmetro --critical, que especifica o ponto em que o armazenamento do banco de dados está ficando cheio. Os valores aceitos incluem 1 KB para um kilobyte, 1 MB para um megabyte e assim por diante, até exabytes (EB). Um número sem uma unidade de capacidade é tratado como sendo expresso em bytes.

      Agora que os comandos necessários estão definidos, você definirá o host (essencialmente o banco de dados) e seus serviços de monitoramento em um arquivo chamado services.cfg. Crie-o usando seu editor favorito:

      • sudo nano /usr/local/nagios/etc/objects/postgresql/services.cfg

      Inclua as seguintes linhas, substituindo db_max_storage_size por um valor referente ao armazenamento disponível do seu banco de dados. É recomendável configurá-lo para 90% do tamanho de armazenamento que você alocou para ele:

      /usr/local/nagios/etc/objects/postgresql/services.cfg

      define host {
            use                    linux-server
            host_name              postgres
            check_command          check_postgres_connection!managed-db
      }
      
      define service {
            use                    generic-service
            host_name              postgres
            service_description    PostgreSQL Connection
            check_command          check_postgres_connection!managed-db
            notification_options   w,u,c,r,f,s
      }
      
      define service {
            use                    generic-service
            host_name              postgres
            service_description    PostgreSQL Database Size
            check_command          check_postgres_database_size!managed-db!db_max_storage_size
            notification_options   w,u,c,r,f,s
      }
      
      define service {
            use                    generic-service
            host_name              postgres
            service_description    PostgreSQL Locks
            check_command          check_postgres_locks!managed-db
            notification_options   w,u,c,r,f,s
      }
      
      define service {
            use                    generic-service
            host_name              postgres
            service_description    PostgreSQL Backends
            check_command          check_postgres_backends!managed-db
            notification_options   w,u,c,r,f,s
      }
      

      Você primeiro define um host, para que o Nagios saiba a que entidade os serviços se relacionam. Em seguida, você cria quatro serviços, que chamam os comandos que você acabou de definir. Cada um deles passa managed-db como argumento, detalhando que o managed-db que você definiu no Passo 2 deve ser monitorado.

      Em relação às opções de notificação, cada serviço especifica que as notificações devem ser enviadas quando o estado do serviço se tornar WARNING,UNKNOWN, CRITICAL,OK (quando se recuperar de uma parada), quando o serviço iniciar oscilando, ou quando a parada programada iniciar ou terminar. Sem atribuir explicitamente um valor a essa opção, nenhuma notificação seria enviada (para os contatos disponíveis), exceto se acionada manualmente.

      Salve e feche o arquivo.

      Em seguida, você precisará dizer explicitamente ao Nagios para ler os arquivos de configuração deste novo diretório, editando o arquivo de configuração geral do Nagios. Abra-o para edição executando o seguinte comando:

      • sudo nano /usr/local/nagios/etc/nagios.cfg

      Encontre esta linha destacada no arquivo:

      /usr/local/nagios/etc/nagios.cfg

      ...
      # directive as shown below:
      
      cfg_dir=/usr/local/nagios/etc/servers
      #cfg_dir=/usr/local/nagios/etc/printers
      ...
      

      Acima dela, adicione a seguinte linha destacada:

      /usr/local/nagios/etc/nagios.cfg

      ...
      cfg_dir=/usr/local/nagios/etc/objects/postgresql
      cfg_dir=/usr/local/nagios/etc/servers
      ...
      

      Salve e feche o arquivo. Esta linha diz ao Nagios para carregar todos os arquivos de configuração a partir do diretório /usr/local/nagios/etc/objects/postgresql, onde seus arquivos de configuração estão localizados.

      Antes de reiniciar o Nagios, verifique a validade da configuração executando o seguinte comando:

      • sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

      O final da saída será semelhante a este:

      Output

      Total Warnings: 0 Total Errors: 0 Things look okay - No serious problems were detected during the pre-flight check

      Isso significa que o Nagios não encontrou erros na configuração. Se ele lhe mostrar um erro, você também verá uma dica sobre o que deu errado, para poder corrigir o erro mais facilmente.

      Para fazer com que o Nagios recarregue sua configuração, reinicie seu serviço executando o seguinte comando:

      • sudo systemctl restart nagios

      Agora você pode navegar até o Nagios no seu navegador. Depois de carregado, clique na opção Services no menu à esquerda. Você verá o host do postgres e uma lista de serviços, junto com seus status atuais:

      PostgreSQL Monitoring Services - Pending

      Em breve, todos eles ficarão verdes e mostrarão o status OK. Você verá a saída do comando na coluna Status Information. Você pode clicar no nome do serviço e ver informações detalhadas sobre seu status e disponibilidade.

      Você adicionou comandos check_postgres, um host e vários serviços à sua instalação do Nagios para monitorar seu banco de dados. Você também verificou que os serviços estão funcionando corretamente, examinando-os por meio da interface web do Nagios. Na próxima etapa, você configurará os alertas baseados no Slack.

      Passo 4 — Configurando Alertas para o Slack

      Nesta seção, você configurará o Nagios para alertá-lo sobre eventos via Slack, publicando-os nos canais desejados em seu workspace.

      Antes de começar, efetue login no workspace desejado no Slack e crie dois canais nos quais você deseja receber mensagens de status do Nagios: um para host e outro para notificações de serviço. Se desejar, você pode criar apenas um canal em que receberá os dois tipos de alertas.

      Em seguida, vá para o app Nagios no Diretório de apps do Slack e click em Add Configuration. Você verá uma página para adicionar a Integração Nagios.

      Slack - Add Nagios Integration

      Click em Add Nagios Integration. Quando a página carregar, role para baixo e tome nota do token, porque você precisará dele mais adiante.

      Slack - Integration Token

      Agora você instalará e configurará o plugin Slack (escrito em Perl) para o Nagios no seu servidor. Primeiro, instale os pré-requisitos necessários do Perl executando o seguinte comando:

      • sudo apt install libwww-perl libcrypt-ssleay-perl -y

      Em seguida, faça o download do plug-in para o diretório de plugins do Nagios:

      • sudo curl https://raw.githubusercontent.com/tinyspeck/services-examples/master/nagios.pl -o slack.pl

      Torne-o executável executando o seguinte comando:

      Agora, você precisará editá-lo para conectar-se ao seu workspace usando o token que você obteve do Slack. Abra-o para edição:

      Localize as seguintes linhas no arquivo:

      /usr/local/nagios/libexec/slack.pl

      ...
      my $opt_domain = "foo.slack.com"; # Your team's domain
      my $opt_token = "your_token"; # The token from your Nagios services page
      ...
      

      Substitua foo.slack.com pelo domínio do seu workspace e your_token pelo seu token de integração do app Nagios, salve e feche o arquivo. O script agora poderá enviar solicitações apropriadas ao Slack, que você testará executando o seguinte comando:

      • ./slack.pl -field slack_channel=#nome_do_seu_canal -field HOSTALIAS="Test Host" -field HOSTSTATE="UP" -field HOSTOUTPUT="Host is UP" -field NOTIFICATIONTYPE="RECOVERY"

      Substitua nome_do_seu_canal pelo nome do canal em que você deseja receber alertas de status. O script exibirá informações sobre a solicitação HTTP feita ao Slack e, se tudo for executado corretamente, a última linha da saída será ok. Se você receber um erro, verifique novamente se o canal do Slack especificado existe no workspace.

      Agora você pode ir para o workspace do Slack e selecionar o canal que você especificou. Você verá uma mensagem de teste vinda do Nagios.

      Slack - Nagios Test Message

      Isso confirma que você configurou corretamente o script para o Slack. Agora você passará a configurar o Nagios para alertá-lo via Slack usando este script.

      Você precisará criar um contato para o Slack e dois comandos que enviarão mensagens para ele. Você armazenará essa configuração em um arquivo chamado slack.cfg, na mesma pasta que os arquivos de configuração anteriores. Crie-o para edição executando o seguinte comando:

      • sudo nano /usr/local/nagios/etc/objects/postgresql/slack.cfg

      Adicione as seguintes linhas:

      /usr/local/nagios/etc/objects/postgresql/slack.cfg

      define contact {
            contact_name                             slack
            alias                                    Slack
            service_notification_period              24x7
            host_notification_period                 24x7
            service_notification_options             w,u,c,f,s,r
            host_notification_options                d,u,r,f,s
            service_notification_commands            notify-service-by-slack
            host_notification_commands               notify-host-by-slack
      }
      
      define command {
            command_name     notify-service-by-slack
            command_line     /usr/local/nagios/libexec/slack.pl -field slack_channel=#service_alerts_channel
      }
      
      define command {
            command_name     notify-host-by-slack
            command_line     /usr/local/nagios/libexec/slack.pl -field slack_channel=#host_alerts_channel
      }
      

      Aqui você define um contato chamado slack, declara que ele pode ser contatado a qualquer momento e especifica quais comandos usar para notificar eventos relacionados ao serviço e ao host. Esses dois comandos são definidos depois e chamam o script que você acabou de configurar. Você precisará substituir service_alerts_channel e host_alerts_channel pelos nomes dos canais em que deseja receber mensagens de serviço e host, respectivamente. Se preferir, você pode usar os mesmos nomes de canais.

      De maneira semelhante à criação do serviço no último passo, é crucial definir as opções de notificação de serviço e host no contato, pois ele determina que tipo de alerta o contato receberá. A omissão dessas opções resultaria no envio de notificações somente quando acionadas manualmente a partir da interface web.

      Quando você terminar de editar, salve e feche o arquivo.

      Para habilitar o alerta através do contato slack que você acabou de definir, você precisará adicioná-lo ao grupo de contatos admin, definido no arquivo de configuração contacts.cfg, localizado em /usr/local/nagios/etc/objects/. Abra-o para edição executando o seguinte comando:

      • sudo nano /usr/local/nagios/etc/objects/contacts.cfg

      Localize o bloco de configuração parecido com este:

      /usr/local/nagios/etc/objects/contacts.cfg

      define contactgroup {
      
          contactgroup_name       admins
          alias                   Nagios Administrators
          members                 nagiosadmin
      }
      

      Adicione slack à lista de membros, assim:

      /usr/local/nagios/etc/objects/contacts.cfg

      define contactgroup {
      
          contactgroup_name       admins
          alias                   Nagios Administrators
          members                 nagiosadmin,slack
      }
      

      Salve e feche o arquivo.

      Por padrão, ao executar scripts, o Nagios não disponibiliza informações de host e serviço por meio de variáveis de ambiente, que é o que o script Slack requer para enviar mensagens significativas. Para remediar isso, você precisará definir a configuração enable_environment_macros em nagios.cfg como 1. Abra-o para edição executando o seguinte comando:

      • sudo nano /usr/local/nagios/etc/nagios.cfg

      Encontre a linha semelhante a essa:

      /usr/local/nagios/etc/nagios.cfg

      enable_environment_macros=0
      

      Altere o valor para 1, assim:

      /usr/local/nagios/etc/nagios.cfg

      enable_environment_macros=1
      

      Salve e feche o arquivo.

      Teste a validade da configuração do Nagios executando o seguinte comando:

      • sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

      O final da saída será semelhante a:

      Output

      Total Warnings: 0 Total Errors: 0 Things look okay - No serious problems were detected during the pre-flight check

      Prossiga e reinicie o Nagios executando o seguinte comando:

      • sudo systemctl restart nagios

      Para testar a integração do Slack, você vai enviar uma notificação personalizada pela interface web. Recarregue a página de status Services do Nagios no seu navegador. Clique no serviço PostgreSQL Backends e clique em Send custom service notification à direita quando a página carregar.

      Nagios - Custom Service Notification

      Digite um comentário de sua escolha e clique em Commit e, em seguida, clique em Done. Você receberá imediatamente uma nova mensagem no Slack.

      Slack - Status Alert From Nagios

      Agora você integrou o Slack ao Nagios, para receber mensagens sobre eventos críticos e alterações de status imediatamente. Você também testou a integração acionando manualmente um evento no Nagios.

      Conclusão

      Agora você tem o Nagios Core configurado para monitorar seu banco de dados PostgreSQL gerenciado e relatar quaisquer mudanças de status e eventos para o Slack, para estar sempre de olho no que está acontecendo com seu banco de dados. Isso permitirá que você reaja rapidamente em caso de emergência, porque você receberá o feed de status em tempo real.

      Se você quiser saber mais sobre os recursos do check_postgres, consulte a documentação, onde você encontrará muito mais comandos que você pode eventualmente usar.

      Para obter mais informações sobre o que você pode fazer com seu banco de dados PostgreSQL gerenciado, visite a doumentação de produto.



      Source link

      How To Monitor Your Managed PostgreSQL Database Using Nagios Core on Ubuntu 18.04


      The author selected the Free and Open Source Fund to receive a donation as part of the Write for DOnations program.

      Introduction

      Database monitoring is key to understanding how a database performs over time. It can help you uncover hidden usage problems and bottlenecks happening in your database. Implementing database monitoring systems can quickly turn out to be a long-term advantage, which will positively influence your infrastructure management process. You’ll be able to swiftly react to status changes of your database and will quickly be notified when monitored services return to normal functioning.

      Nagios Core is a popular monitoring system that you can use to monitor your managed database. The benefits of using Nagios for this task are its versatility—it’s easy to configure and use—a large repository of available plugins, and most importantly, integrated alerting.

      In this tutorial, you will set up PostgreSQL database monitoring in Nagios Core using the check_postgres Nagios plugin and set up Slack-based alerting. In the end, you’ll have a monitoring system in place for your managed PostgreSQL database, and will be notified of status changes of various functionality immediately.

      Prerequisites

      • An Ubuntu 18.04 server with root privileges, and a secondary, non-root account. You can set this up by following this initial server setup guide. For this tutorial the non-root user is sammy.

      • Nagios Core installed on your server. To achieve this, complete the first five steps of the How To Install Nagios 4 and Monitor Your Servers on Ubuntu 18.04 tutorial.

      • A DigitalOcean account and a PostgreSQL managed database provisioned from DigitalOcean with connection information available. Make sure that your server’s IP address is on the whitelist. To learn more about DigitalOcean Managed Databases, visit the product docs.

      • A Slack account with full access, added to a workspace where you’ll want to receive status updates.

      Step 1 — Installing check_postgres

      In this section, you’ll download the latest version of the check_postgres plugin from Github and make it available to Nagios Core. You’ll also install the PostgreSQL client (psql), so that check_postgres will be able to connect to your managed database.

      Start off by installing the PostgreSQL client by running the following command:

      • sudo apt install postgresql-client

      Next, you’ll download check_postgres to your home directory. First, navigate to it:

      Head over to the Github releases page and copy the link of the latest version of the plugin. At the time of writing, the latest version of check_postgres was 2.24.0; keep in mind that this will update, and where possible it's best practice to use the latest version.

      Now download it using curl:

      • curl -LO https://github.com/bucardo/check_postgres/releases/download/2.24.0/check_postgres-2.24.0.tar.gz

      Extract it using the following command:

      • tar xvf check_postgres-*.tar.gz

      This will create a directory with the same name as the file you have downloaded. That folder contains the check_postgres executable, which you'll need to copy to the directory where Nagios stores its plugins (usually /usr/local/nagios/libexec/). Copy it by running the following command:

      • sudo cp check_postgres-*/check_postgres.pl /usr/local/nagios/libexec/

      Next, you'll need to give the nagios user ownership of it, so that it can be run from Nagios:

      • sudo chown nagios:nagios /usr/local/nagios/libexec/check_postgres.pl

      check_postgres is now available to Nagios and can be used from it. However, it provides a lot of commands pertaining to different aspects of PostgreSQL, and for better service maintainability, it's better to break them up so that they can be called separately. You'll achieve this by creating a symlink to every check_postgres command in the plugin directory.

      Navigate to the directory where Nagios stores plugins by running the following command:

      • cd /usr/local/nagios/libexec

      Then, create the symlinks with:

      • sudo perl check_postgres.pl --symlinks

      The output will look like this:

      Output

      Created "check_postgres_archive_ready" Created "check_postgres_autovac_freeze" Created "check_postgres_backends" Created "check_postgres_bloat" Created "check_postgres_checkpoint" Created "check_postgres_cluster_id" Created "check_postgres_commitratio" Created "check_postgres_connection" Created "check_postgres_custom_query" Created "check_postgres_database_size" Created "check_postgres_dbstats" Created "check_postgres_disabled_triggers" Created "check_postgres_disk_space" Created "check_postgres_fsm_pages" Created "check_postgres_fsm_relations" Created "check_postgres_hitratio" Created "check_postgres_hot_standby_delay" Created "check_postgres_index_size" Created "check_postgres_indexes_size" Created "check_postgres_last_analyze" Created "check_postgres_last_autoanalyze" Created "check_postgres_last_autovacuum" Created "check_postgres_last_vacuum" Created "check_postgres_listener" Created "check_postgres_locks" Created "check_postgres_logfile" Created "check_postgres_new_version_bc" Created "check_postgres_new_version_box" Created "check_postgres_new_version_cp" Created "check_postgres_new_version_pg" Created "check_postgres_new_version_tnm" Created "check_postgres_pgagent_jobs" Created "check_postgres_pgb_pool_cl_active" Created "check_postgres_pgb_pool_cl_waiting" Created "check_postgres_pgb_pool_maxwait" Created "check_postgres_pgb_pool_sv_active" Created "check_postgres_pgb_pool_sv_idle" Created "check_postgres_pgb_pool_sv_login" Created "check_postgres_pgb_pool_sv_tested" Created "check_postgres_pgb_pool_sv_used" Created "check_postgres_pgbouncer_backends" Created "check_postgres_pgbouncer_checksum" Created "check_postgres_prepared_txns" Created "check_postgres_query_runtime" Created "check_postgres_query_time" Created "check_postgres_relation_size" Created "check_postgres_replicate_row" Created "check_postgres_replication_slots" Created "check_postgres_same_schema" Created "check_postgres_sequence" Created "check_postgres_settings_checksum" Created "check_postgres_slony_status" Created "check_postgres_table_size" Created "check_postgres_timesync" Created "check_postgres_total_relation_size" Created "check_postgres_txn_idle" Created "check_postgres_txn_time" Created "check_postgres_txn_wraparound" Created "check_postgres_version" Created "check_postgres_wal_files"

      Perl listed all the functions it created a symlink for. These can now be executed from the command line as usual.

      You've downloaded and installed the check_postgres plugin. You have also created symlinks to all the commands of the plugin, so that they can be used individually from Nagios. In the next step, you'll create a connection service file, which check_postgres will use to connect to your managed database.

      Step 2 — Configuring Your Database

      In this section, you will create a PostgreSQL connection service file containing the connection information of your database. Then, you will test the connection data by invoking check_postgres on it.

      The connection service file is by convention called pg_service.conf, and must be located under /etc/postgresql-common/. Create it for editing with your favorite editor (for example, nano):

      • sudo nano /etc/postgresql-common/pg_service.conf

      Add the following lines, replacing the highlighted placeholders with the actual values shown in your Managed Database Control Panel under the section Connection Details:

      /etc/postgresql-common/pg_service.conf

      [managed-db]
      host=host
      port=port
      user=username
      password=password
      dbname=defaultdb
      sslmode=require
      

      The connection service file can house multiple database connection info groups. The beginning of a group is signaled by putting its name in square brackets. After that comes the connection parameters (host, port, user, password, and so on), separated by new lines, which must be given a value.

      Save and close the file when you are finished.

      You'll now test the validity of the configuration by connecting to the database via check_postgres by running the following command:

      • ./check_postgres.pl --dbservice=managed-db --action=connection

      Here, you tell check_postgres which database connection info group to use with the parameter --dbservice, and also specify that it should only try to connect to it by specifying connection as the action.

      Your output will look similar to this:

      Output

      POSTGRES_CONNECTION OK: service=managed-db version 11.4 | time=0.10s

      This means that check_postgres succeeded in connecting to the database, according to the parameters from pg_service.conf. If you get an error, double check what you have just entered in that config file.

      You've created and filled out a PostgreSQL connection service file, which works as a connection string. You have also tested the connection data by running check_postgres on it and observing the output. In the next step, you will configure Nagios to monitor various parts of your database.

      Step 3 — Creating Monitoring Services in Nagios

      Now you will configure Nagios to watch over various metrics of your database by defining a host and multiple services, which will call the check_postgres plugin and its symlinks.

      Nagios stores your custom configuration files under /usr/local/nagios/etc/objects. New files you add there must be manually enabled in the central Nagios config file, located at /usr/local/nagios/etc/nagios.cfg. You'll now define commands, a host, and multiple services, which you'll use to monitor your managed database in Nagios.

      First, create a folder under /usr/local/nagios/etc/objects to store your PostgreSQL related configuration by running the following command:

      • sudo mkdir /usr/local/nagios/etc/objects/postgresql

      You'll store Nagios commands for check_nagios in a file named commands.cfg. Create it for editing:

      • sudo nano /usr/local/nagios/etc/objects/postgresql/commands.cfg

      Add the following lines:

      /usr/local/nagios/etc/objects/postgresql/commands.cfg

      define command {
          command_name           check_postgres_connection
          command_line           /usr/local/nagios/libexec/check_postgres_connection --dbservice=$ARG1$
      }
      
      define command {
          command_name           check_postgres_database_size
          command_line           /usr/local/nagios/libexec/check_postgres_database_size --dbservice=$ARG1$ --critical='$ARG2$'
      }
      
      define command {
          command_name           check_postgres_locks
          command_line           /usr/local/nagios/libexec/check_postgres_locks --dbservice=$ARG1$
      }
      
      define command {
          command_name           check_postgres_backends
          command_line           /usr/local/nagios/libexec/check_postgres_backends --dbservice=$ARG1$
      }
      

      Save and close the file.

      In this file, you define four Nagios commands that call different parts of the check_postgres plugin (checking connectivity, getting the number of locks and connections, and the size of the whole database). They all accept an argument that is passed to the --dbservice parameter, and specify which of the databases defined in pg_service.conf to connect to.

      The check_postgres_database_size command accepts a second argument that gets passed to the --critical parameter, which specifies the point at which the database storage is becoming full. Accepted values include 1 KB for a kilobyte, 1 MB for a megabyte, and so on, up to exabytes (EB). A number without a capacity unit is treated as being expressed in bytes.

      Now that the necessary commands are defined, you'll define the host (essentially, the database) and its monitoring services in a file named services.cfg. Create it using your favorite editor:

      • sudo nano /usr/local/nagios/etc/objects/postgresql/services.cfg

      Add the following lines, replacing db_max_storage_size with a value pertaining to the available storage of your database. It is recommended to set it to 90 percent of the storage size you have allocated to it:

      /usr/local/nagios/etc/objects/postgresql/services.cfg

      define host {
            use                    linux-server
            host_name              postgres
            check_command          check_postgres_connection!managed-db
      }
      
      define service {
            use                    generic-service
            host_name              postgres
            service_description    PostgreSQL Connection
            check_command          check_postgres_connection!managed-db
            notification_options   w,u,c,r,f,s
      }
      
      define service {
            use                    generic-service
            host_name              postgres
            service_description    PostgreSQL Database Size
            check_command          check_postgres_database_size!managed-db!db_max_storage_size
            notification_options   w,u,c,r,f,s
      }
      
      define service {
            use                    generic-service
            host_name              postgres
            service_description    PostgreSQL Locks
            check_command          check_postgres_locks!managed-db
            notification_options   w,u,c,r,f,s
      }
      
      define service {
            use                    generic-service
            host_name              postgres
            service_description    PostgreSQL Backends
            check_command          check_postgres_backends!managed-db
            notification_options   w,u,c,r,f,s
      }
      

      You first define a host, so that Nagios will know what entity the services relate to. Then, you create four services, which call the commands you just defined. Each one passes managed-db as the argument, detailing that the managed-db you defined in Step 2 should be monitored.

      Regarding notification options, each service specifies that notifications should be sent out when the service state becomes WARNING, UNKNOWN, CRITICAL, OK (when it recovers from downtime), when the service starts flapping, or when scheduled downtime starts or ends. Without explicitly giving this option a value, no notifications would be sent out (to available contacts) at all, except if triggered manually.

      Save and close the file.

      Next, you'll need to explicitly tell Nagios to read config files from this new directory, by editing the general Nagios config file. Open it for editing by running the following command:

      • sudo nano /usr/local/nagios/etc/nagios.cfg

      Find this highlighted line in the file:

      /usr/local/nagios/etc/nagios.cfg

      ...
      # directive as shown below:
      
      cfg_dir=/usr/local/nagios/etc/servers
      #cfg_dir=/usr/local/nagios/etc/printers
      ...
      

      Above it, add the following highlighted line:

      /usr/local/nagios/etc/nagios.cfg

      ...
      cfg_dir=/usr/local/nagios/etc/objects/postgresql
      cfg_dir=/usr/local/nagios/etc/servers
      ...
      

      Save and close the file. This line tells Nagios to load all config files from the /usr/local/nagios/etc/objects/postgresql directory, where your configuration files are located.

      Before restarting Nagios, check the validity of the configuration by running the following command:

      • sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

      The end of the output will look similar to this:

      Output

      Total Warnings: 0 Total Errors: 0 Things look okay - No serious problems were detected during the pre-flight check

      This means that Nagios found no errors in the configuration. If it shows you an error, you'll also see a hint as to what went wrong, so you'll be able to fix the error more easily.

      To make Nagios reload its configuration, restart its service by running the following command:

      • sudo systemctl restart nagios

      You can now navigate to Nagios in your browser. Once it loads, press on the Services option from the left-hand menu. You'll see the postgres host and a list of services, along with their current statuses:

      PostgreSQL Monitoring Services - Pending

      They will all soon turn to green and show an OK status. You'll see the command output under the Status Information column. You can click on the service name and see detailed information about its status and availability.

      You've added check_postgres commands, a host, and multiple services to your Nagios installation to monitor your database. You've also checked that the services are working properly by examining them via the Nagios web interface. In the next step, you will configure Slack-based alerting.

      Step 4 — Configuring Slack Alerting

      In this section, you will configure Nagios to alert you about events via Slack, by posting them into desired channels in your workspace.

      Before you start, log in to your desired workspace on Slack and create two channels where you'll want to receive status messages from Nagios: one for host, and the other one for service notifications. If you wish, you can create only one channel where you'll receive both kinds of alerts.

      Then, head over to the Nagios app in the Slack App Directory and press on Add Configuration. You'll see a page for adding the Nagios Integration.

      Slack - Add Nagios Integration

      Press on Add Nagios Integration. When the page loads, scroll down and take note of the token, because you'll need it further on.

      Slack - Integration Token

      You'll now install and configure the Slack plugin (written in Perl) for Nagios on your server. First, install the required Perl prerequisites by running the following command:

      • sudo apt install libwww-perl libcrypt-ssleay-perl -y

      Then, download the plugin to your Nagios plugin directory:

      • sudo curl https://raw.githubusercontent.com/tinyspeck/services-examples/master/nagios.pl -o slack.pl

      Make it executable by running the following command:

      Now, you'll need to edit it to connect to your workspace using the token you got from Slack. Open it for editing:

      Find the following lines in the file:

      /usr/local/nagios/libexec/slack.pl

      ...
      my $opt_domain = "foo.slack.com"; # Your team's domain
      my $opt_token = "your_token"; # The token from your Nagios services page
      ...
      

      Replace foo.slack.com with your workspace domain and your_token with your Nagios app integration token, then save and close the file. The script will now be able to send proper requests to Slack, which you'll now test by running the following command:

      • ./slack.pl -field slack_channel=#your_channel_name -field HOSTALIAS="Test Host" -field HOSTSTATE="UP" -field HOSTOUTPUT="Host is UP" -field NOTIFICATIONTYPE="RECOVERY"

      Replace your_channel_name with the name of the channel where you'll want to receive status alerts. The script will output information about the HTTP request it made to Slack, and if everything went through correctly, the last line of the output will be ok. If you get an error, double check if the Slack channel you specified exists in the workspace.

      You can now head over to your Slack workspace and select the channel you specified. You'll see a test message coming from Nagios.

      Slack - Nagios Test Message

      This confirms that you have properly configured the Slack script. You'll now move on to configuring Nagios to alert you via Slack using this script.

      You'll need to create a contact for Slack and two commands that will send messages to it. You'll store this config in a file named slack.cfg, in the same folder as the previous config files. Create it for editing by running the following command:

      • sudo nano /usr/local/nagios/etc/objects/postgresql/slack.cfg

      Add the following lines:

      /usr/local/nagios/etc/objects/postgresql/slack.cfg

      define contact {
            contact_name                             slack
            alias                                    Slack
            service_notification_period              24x7
            host_notification_period                 24x7
            service_notification_options             w,u,c,f,s,r
            host_notification_options                d,u,r,f,s
            service_notification_commands            notify-service-by-slack
            host_notification_commands               notify-host-by-slack
      }
      
      define command {
            command_name     notify-service-by-slack
            command_line     /usr/local/nagios/libexec/slack.pl -field slack_channel=#service_alerts_channel
      }
      
      define command {
            command_name     notify-host-by-slack
            command_line     /usr/local/nagios/libexec/slack.pl -field slack_channel=#host_alerts_channel
      }
      

      Here you define a contact named slack, state that it can be contacted anytime and specify which commands to use for notifying service and host related events. Those two commands are defined after it and call the script you have just configured. You'll need to replace service_alerts_channel and host_alerts_channel with the names of the channels where you want to receive service and host messages, respectively. If preferred, you can use the same channel names.

      Similarly to the service creation in the last step, setting service and host notification options on the contact is crucial, because it governs what kind of alerts the contact will receive. Omitting those options would result in sending out notifications only when manually triggered from the web interface.

      When you are done with editing, save and close the file.

      To enable alerting via the slack contact you just defined, you'll need to add it to the admin contact group, defined in the contacts.cfg config file, located under /usr/local/nagios/etc/objects/. Open it for editing by running the following command:

      • sudo nano /usr/local/nagios/etc/objects/contacts.cfg

      Find the config block that looks like this:

      /usr/local/nagios/etc/objects/contacts.cfg

      define contactgroup {
      
          contactgroup_name       admins
          alias                   Nagios Administrators
          members                 nagiosadmin
      }
      

      Add slack to the list of members, like so:

      /usr/local/nagios/etc/objects/contacts.cfg

      define contactgroup {
      
          contactgroup_name       admins
          alias                   Nagios Administrators
          members                 nagiosadmin,slack
      }
      

      Save and close the file.

      By default when running scripts, Nagios does not make host and service information available via environment variables, which is what the Slack script requires in order to send meaningful messages. To remedy this, you'll need to set the enable_environment_macros setting in nagios.cfg to 1. Open it for editing by running the following command:

      • sudo nano /usr/local/nagios/etc/nagios.cfg

      Find the line that looks like this:

      /usr/local/nagios/etc/nagios.cfg

      enable_environment_macros=0
      

      Change the value to 1, like so:

      /usr/local/nagios/etc/nagios.cfg

      enable_environment_macros=1
      

      Save and close the file.

      Test the validity of the Nagios configuration by running the following command:

      • sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

      The end of the output will look like:

      Output

      Total Warnings: 0 Total Errors: 0 Things look okay - No serious problems were detected during the pre-flight check

      Proceed to restart Nagios by running the following command:

      • sudo systemctl restart nagios

      To test the Slack integration, you'll send out a custom notification via the web interface. Reload the Nagios Services status page in your browser. Press on the PostgreSQL Backends service and press on Send custom service notification on the right when the page loads.

      Nagios - Custom Service Notification

      Type in a comment of your choice and press on Commit, and then press on Done. You'll immediately receive a new message in Slack.

      Slack - Status Alert From Nagios

      You have now integrated Slack with Nagios, so you'll receive messages about critical events and status changes immediately. You've also tested the integration by manually triggering an event from within Nagios.

      Conclusion

      You now have Nagios Core configured to watch over your managed PostgreSQL database and report any status changes and events to Slack, so you'll always be in the loop of what is happening to your database. This will allow you to swiftly react in case of an emergency, because you'll be getting the status feed in real time.

      If you'd like to learn more about the features of check_postgres, check out its docs, where you'll find a lot more commands that you can possibly use.

      For more information about what you can do with your PostgreSQL Managed Database, visit the product docs.



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