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      How To Install and Configure Zabbix to Securely Monitor Remote Servers on Ubuntu 18.04


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

      Introduction

      Zabbix is open-source monitoring software for networks and applications. It offers real-time monitoring of thousands of metrics collected from servers, virtual machines, network devices, and web applications. These metrics can help you determine the current health of your IT infrastructure and detect problems with hardware or software components before customers complain. Useful information is stored in a database so you can analyze data over time and improve the quality of provided services, or plan upgrades of your equipment.

      Zabbix uses several options for collecting metrics, including agentless monitoring of user services and client-server architecture. To collect server metrics, it uses a small agent on the monitored client to gather data and send it to the Zabbix server. Zabbix supports encrypted communication between the server and connected clients, so your data is protected while it travels over insecure networks.

      The Zabbix server stores its data in a relational database powered by MySQL, PostgreSQL, or Oracle. You can also store historical data in nosql databases like Elasticsearch and TimescaleDB. Zabbix provides a web interface so you can view data and configure system settings.

      In this tutorial, you will configure two machines. One will be configured as the server, and the other as a client that you’ll monitor. The server will use a MySQL database to record monitoring data and use Apache to serve the web interface.

      Prerequisites

      To follow this tutorial, you will need:

      • Two Ubuntu 18.04 servers set up by following the Initial Server Setup Guide for Ubuntu 18.04, including a non-root user with sudo privileges and a firewall configured with ufw. On one server, you will install Zabbix; this tutorial will refer to this as the Zabbix server. It will monitor your second server; this second server will be referred to as the second Ubuntu server.

      • The server that will run the Zabbix server needs Apache, MySQL, and PHP installed. Follow this guide to configure those on your Zabbix server.

      Additionally, because the Zabbix Server is used to access valuable information about your infrastructure that you would not want unauthorized users to access, it’s important that you keep your server secure by installing a TLS/SSL certificate. This is optional but strongly encouraged. You can follow the Let’s Encrypt on Ubuntu 18.04 guide to obtain the free TLS/SSL certificate.

      Step 1 — Installing the Zabbix Server

      First, you need to install Zabbix on the server where you installed MySQL, Apache, and PHP. Log into this machine as your non-root user:

      • ssh sammy@zabbix_server_ip_address

      Zabbix is available in Ubuntu’s package manager, but it’s outdated, so use the official Zabbix repository to install the latest stable version. Download and install the repository configuration package:

      • wget https://repo.zabbix.com/zabbix/4.2/ubuntu/pool/main/z/zabbix-release/zabbix-release_4.2-1+bionic_all.deb
      • sudo dpkg -i zabbix-release_4.2-1+bionic_all.deb

      You will see the following output:

      Output

      Selecting previously unselected package zabbix-release. (Reading database ... 61483 files and directories currently installed.) Preparing to unpack zabbix-release_4.2-1+bionic_all.deb ... Unpacking zabbix-release (4.2-1+bionicc) ... Setting up zabbix-release (4.2-1+bionicc) ...

      Update the package index so the new repository is included:

      Then install the Zabbix server and web frontend with MySQL database support:

      • sudo apt install zabbix-server-mysql zabbix-frontend-php

      Also, install the Zabbix agent, which will let you collect data about the Zabbix server status itself.

      • sudo apt install zabbix-agent

      Before you can use Zabbix, you have to set up a database to hold the data that the Zabbix server will collect from its agents. You can do this in the next step.

      Step 2 — Configuring the MySQL Database for Zabbix

      You need to create a new MySQL database and populate it with some basic information in order to make it suitable for Zabbix. You'll also create a specific user for this database so Zabbix isn't logging into MySQL with the root account.

      Log into MySQL as the root user using the root password that you set up during the MySQL server installation:

      Create the Zabbix database with UTF-8 character support:

      • create database zabbix character set utf8 collate utf8_bin;

      Then create a user that the Zabbix server will use, give it access to the new database, and set the password for the user:

      • grant all privileges on zabbix.* to zabbix@localhost identified by 'your_zabbix_mysql_password';

      Then apply these new permissions:

      That takes care of the user and the database. Exit out of the database console.

      Next you have to import the initial schema and data. The Zabbix installation provided you with a file that sets this up.

      Run the following command to set up the schema and import the data into the zabbix database. Use zcat since the data in the file is compressed.

      • zcat /usr/share/doc/zabbix-server-mysql/create.sql.gz | mysql -uzabbix -p zabbix

      Enter the password for the zabbix MySQL user that you configured when prompted.

      This command will not output any errors if it was successful. If you see the error ERROR 1045 (28000): Access denied for userzabbix@'localhost' (using password: YES) then make sure you used the password for the zabbix user and not the root user.

      In order for the Zabbix server to use this database, you need to set the database password in the Zabbix server configuration file. Open the configuration file in your preferred text editor. This tutorial will use nano:

      • sudo nano /etc/zabbix/zabbix_server.conf

      Look for the following section of the file:

      /etc/zabbix/zabbix_server.conf

      ### Option: DBPassword                           
      #       Database password. Ignored for SQLite.   
      #       Comment this line if no password is used.
      #                                                
      # Mandatory: no                                  
      # Default:                                       
      # DBPassword=
      

      These comments in the file explain how to connect to the database. You need to set the DBPassword value in the file to the password for your database user. Add this line below those comments to configure the database:

      /etc/zabbix/zabbix_server.conf

      ...
      DBPassword=your_zabbix_mysql_password
      

      Save and close zabbix_server.conf by pressing CTRL+X, followed by Y and then ENTER if you're using nano.

      That takes care of the Zabbix server configuration. Next, you will make some modifications to your PHP setup in order for the Zabbix web interface to work properly.

      Step 3 — Configuring PHP for Zabbix

      The Zabbix web interface is written in PHP and requires some special PHP server settings. The Zabbix installation process created an Apache configuration file that contains these settings. It is located in the directory /etc/zabbix and is loaded automatically by Apache. You need to make a small change to this file, so open it up with the following:

      • sudo nano /etc/zabbix/apache.conf

      The file contains PHP settings that meet the necessary requirements for the Zabbix web interface. However, the timezone setting is commented out by default. To make sure that Zabbix uses the correct time, you need to set the appropriate timezone.

      /etc/zabbix/apache.conf

      ...
      <IfModule mod_php7.c>
          php_value max_execution_time 300
          php_value memory_limit 128M
          php_value post_max_size 16M
          php_value upload_max_filesize 2M
          php_value max_input_time 300
          php_value always_populate_raw_post_data -1
          # php_value date.timezone Europe/Riga
      </IfModule>
      

      Uncomment the timezone line, highlighted in the preceding code block, and change it to your timezone. You can use this list of supported time zones to find the right one for you. Then save and close the file.

      Now restart Apache to apply these new settings.

      • sudo systemctl restart apache2

      You can now start the Zabbix server.

      • sudo systemctl start zabbix-server

      Then check whether the Zabbix server is running properly:

      • sudo systemctl status zabbix-server

      You will see the following status:

      Output

      ● zabbix-server.service - Zabbix Server Loaded: loaded (/lib/systemd/system/zabbix-server.service; disabled; vendor preset: enabled) Active: active (running) since Fri 2019-04-05 08:50:54 UTC; 3s ago Process: 16497 ExecStart=/usr/sbin/zabbix_server -c $CONFFILE (code=exited, status=0/SUCCESS) ...

      Finally, enable the server to start at boot time:

      • sudo systemctl enable zabbix-server

      The server is set up and connected to the database. Next, set up the web frontend.

      Note: As mentioned in the Prerequisites section, it is recommended that you enable SSL/TLS on your server. You can follow this tutorial now to obtain a free SSL certificate for Apache on Ubuntu 18.04. After obtaining your SSL/TLS certificates, you can come back and complete this tutorial.

      Step 4 — Configuring Settings for the Zabbix Web Interface

      The web interface lets you see reports and add hosts that you want to monitor, but it needs some initial setup before you can use it. Launch your browser and go to the address http://zabbix_server_name/zabbix/. On the first screen, you will see a welcome message. Click Next step to continue.

      On the next screen, you will see the table that lists all of the prerequisites to run Zabbix.

      Prerequisites

      All of the values in this table must be OK, so verify that they are. Be sure to scroll down and look at all of the prerequisites. Once you've verified that everything is ready to go, click Next step to proceed.

      The next screen asks for database connection information.

      DB Connection

      You told the Zabbix server about your database, but the Zabbix web interface also needs access to the database to manage hosts and read data. Therefore enter the MySQL credentials you configured in Step 2 and click Next step to proceed.

      On the next screen, you can leave the options at their default values.

      Zabbix Server Details

      The Name is optional; it is used in the web interface to distinguish one server from another in case you have several monitoring servers. Click Next step to proceed.

      The next screen will show the pre-installation summary so you can confirm everything is correct.

      Summary

      Click Next step to proceed to the final screen.

      The web interface setup is complete! This process creates the configuration file /usr/share/zabbix/conf/zabbix.conf.php which you could back up and use in the future. Click Finish to proceed to the login screen. The default user is Admin and the password is zabbix.

      Before you log in, set up the Zabbix agent on your second Ubuntu server.

      Step 5 — Installing and Configuring the Zabbix Agent

      Now you need to configure the agent software that will send monitoring data to the Zabbix server.

      Log in to the second Ubuntu server:

      • ssh sammy@second_ubuntu_server_ip_address

      Then, just like on the Zabbix server, run the following commands to install the repository configuration package:

      • wget https://repo.zabbix.com/zabbix/4.2/ubuntu/pool/main/z/zabbix-release/zabbix-release_4.2-1+bionic_all.deb
      • sudo dpkg -i zabbix-release_4.2-1+bionic_all.deb

      Next, update the package index:

      Then install the Zabbix agent:

      • sudo apt install zabbix-agent

      While Zabbix supports certificate-based encryption, setting up a certificate authority is beyond the scope of this tutorial, but you can use pre-shared keys (PSK) to secure the connection between the server and agent.

      First, generate a PSK:

      • sudo sh -c "openssl rand -hex 32 > /etc/zabbix/zabbix_agentd.psk"

      Show the key so you can copy it somewhere. You will need it to configure the host.

      • cat /etc/zabbix/zabbix_agentd.psk

      The key will look something like this:

      Output

      12eb854dea38ac9ee7d1ded2d74cee6262b0a56710f6946f7913d674ab82cdd4

      Now edit the Zabbix agent settings to set up its secure connection to the Zabbix server. Open the agent configuration file in your text editor:

      • sudo nano /etc/zabbix/zabbix_agentd.conf

      Each setting within this file is documented via informative comments throughout the file, but you only need to edit some of them.

      First you have to edit the IP address of the Zabbix server. Find the following section:

      /etc/zabbix/zabbix_agentd.conf

      ...
      ### Option: Server
      #       List of comma delimited IP addresses (or hostnames) of Zabbix servers.
      #       Incoming connections will be accepted only from the hosts listed here.
      #       If IPv6 support is enabled then '127.0.0.1', '::127.0.0.1', '::ffff:127.0.0.1' are treated equally.
      #
      # Mandatory: no
      # Default:
      # Server=
      
      Server=127.0.0.1
      ...
      

      Change the default value to the IP of your Zabbix server:

      /etc/zabbix/zabbix_agentd.conf

      ...
      Server=zabbix_server_ip_address
      ...
      

      Next, find the section that configures the secure connection to the Zabbix server and enable pre-shared key support. Find the TLSConnect section, which looks like this:

      /etc/zabbix/zabbix_agentd.conf

      ...
      ### Option: TLSConnect
      #       How the agent should connect to server or proxy. Used for active checks.
      #       Only one value can be specified:
      #               unencrypted - connect without encryption
      #               psk         - connect using TLS and a pre-shared key
      #               cert        - connect using TLS and a certificate
      #
      # Mandatory: yes, if TLS certificate or PSK parameters are defined (even for 'unencrypted' connection)
      # Default:
      # TLSConnect=unencrypted
      ...
      

      Then add this line to configure pre-shared key support:

      /etc/zabbix/zabbix_agentd.conf

      ...
      TLSConnect=psk
      ...
      

      Next, locate the TLSAccept section, which looks like this:

      /etc/zabbix/zabbix_agentd.conf

      ...
      ### Option: TLSAccept
      #       What incoming connections to accept.
      #       Multiple values can be specified, separated by comma:
      #               unencrypted - accept connections without encryption
      #               psk         - accept connections secured with TLS and a pre-shared key
      #               cert        - accept connections secured with TLS and a certificate
      #
      # Mandatory: yes, if TLS certificate or PSK parameters are defined (even for 'unencrypted' connection)
      # Default:
      # TLSAccept=unencrypted
      ...
      

      Configure incoming connections to support pre-shared keys by adding this line:

      /etc/zabbix/zabbix_agentd.conf

      ...
      TLSAccept=psk
      ...
      

      Next, find the TLSPSKIdentity section, which looks like this:

      /etc/zabbix/zabbix_agentd.conf

      ...
      ### Option: TLSPSKIdentity
      #       Unique, case sensitive string used to identify the pre-shared key.
      #
      # Mandatory: no
      # Default:
      # TLSPSKIdentity=
      ...
      

      Choose a unique name to identify your pre-shared key by adding this line:

      /etc/zabbix/zabbix_agentd.conf

      ...
      TLSPSKIdentity=PSK 001
      ...
      

      You'll use this as the PSK ID when you add your host through the Zabbix web interface.

      Then set the option that points to your previously created pre-shared key. Locate the TLSPSKFile option:

      /etc/zabbix/zabbix_agentd.conf

      ...
      ### Option: TLSPSKFile
      #       Full pathname of a file containing the pre-shared key.
      #
      # Mandatory: no
      # Default:
      # TLSPSKFile=
      ...
      

      Add this line to point the Zabbix agent to your PSK file you created:

      /etc/zabbix/zabbix_agentd.conf

      ...
      TLSPSKFile=/etc/zabbix/zabbix_agentd.psk
      ...
      

      Save and close the file. Now you can restart the Zabbix agent and set it to start at boot time:

      • sudo systemctl restart zabbix-agent
      • sudo systemctl enable zabbix-agent

      For good measure, check that the Zabbix agent is running properly:

      • sudo systemctl status zabbix-agent

      You will see the following status, indicating the agent is running:

      Output

      ● zabbix-agent.service - Zabbix Agent Loaded: loaded (/lib/systemd/system/zabbix-agent.service; enabled; vendor preset: enabled) Active: active (running) since Fri 2019-04-05 09:03:04 UTC; 1s ago ...

      The agent will listen on port 10050 for connections from the server. Configure UFW to allow connections to this port:

      You can learn more about UFW in How To Set Up a Firewall with UFW on Ubuntu 18.04.

      Your agent is now ready to send data to the Zabbix server. But in order to use it, you have to link to it from the server's web console. In the next step, you will complete the configuration.

      Step 6 — Adding the New Host to the Zabbix Server

      Installing an agent on a server you want to monitor is only half of the process. Each host you want to monitor needs to be registered on the Zabbix server, which you can do through the web interface.

      Log in to the Zabbix Server web interface by navigating to the address http://zabbix_server_name/zabbix/.

      The Zabbix login screen

      When you have logged in, click on Configuration, and then Hosts in the top navigation bar. Then click the Create host button in the top right corner of the screen. This will open the host configuration page.

      Creating a host

      Adjust the Host name and IP address to reflect the host name and IP address of your second Ubuntu server, then add the host to a group. You can select an existing group, for example Linux servers, or create your own group. The host can be in multiple groups. To do this, enter the name of an existing or new group in the Groups field and select the desired value from the proposed list.

      Once you've added the group, click the Templates tab.

      Adding a template to the host

      Type Template OS Linux in the Search field and then click Add to add this template to the host.

      Next, navigate to the Encryption tab. Select PSK for both Connections to host and Connections from host. Then set PSK identity to PSK 001, which is the value of the TLSPSKIdentity setting of the Zabbix agent you configured previously. Then set PSK value to the key you generated for the Zabbix agent. It's the one stored in the file /etc/zabbix/zabbix_agentd.psk on the agent machine.

      Setting up the encryption

      Finally, click the Add button at the bottom of the form to create the host.

      You will see your new host in the list. Wait for a minute and reload the page to see green labels indicating that everything is working fine and the connection is encrypted.

      Zabbix shows your new host

      If you have additional servers you need to monitor, log in to each host, install the Zabbix agent, generate a PSK, configure the agent, and add the host to the web interface following the same steps you followed to add your first host.

      The Zabbix server is now monitoring your second Ubuntu server. Now, set up email notifications to be notified about problems.

      Step 7 — Configuring Email Notifications

      Zabbix automatically supports several types of notifications: email, Jabber, SMS, etc. You can also use alternative notification methods, such as Telegram or Slack. You can see the full list of integrations here.

      The simplest communication method is email, and this tutorial will configure notifications for this media type.

      Click on Administration, and then Media types in the top navigation bar. You will see the list of all media types. Click on Email.

      Adjust the SMTP options according to the settings provided by your email service. This tutorial uses Gmail's SMTP capabilities to set up email notifications; if you would like more information about setting this up, see How To Use Google's SMTP Server.


      Note: If you use 2-Step Verification with Gmail, you need to generate an App Password for Zabbix. You don't need to remember it, you’ll only have to enter an App password once during setup. You will find instructions on how to generate this password in the Google Help Center.

      You can also choose the message format—html or plain text. Finally, click the Update button at the bottom of the form to update the email parameters.

      Setting up email

      Now, create a new user. Click on Administration, and then Users in the top navigation bar. You will see the list of users. Then click the Create user button in the top right corner of the screen. This will open the user configuration page.

      Creating a user

      Enter the new username in the Alias field and set up a new password. Next, add the user to the administrator's group. Type Zabbix administrators in the Groups field and select it from the proposed list.

      Once you've added the group, click the Media tab and click on the Add underlined link. You will see a pop-up window.

      Adding an email

      Enter your email address in the Send to field. You can leave the rest of the options at the default values. Click the Add button at the bottom to submit.

      Now navigate to the Permissions tab. Select Zabbix Super Admin from the User type drop-down menu.

      Finally, click the Add button at the bottom of the form to create the user.

      Now you need to enable notifications. Click on the Configuration tab, and then Actions in the top navigation bar. You will see a pre-configured action, which is responsible for sending notifications to all Zabbix administrators. You can review and change the settings by clicking on its name. For the purposes of this tutorial, use the default parameters. To enable the action, click on the red Disabled link in the Status column.

      Now you are ready to receive alerts. In the next step, you will generate one to test your notification setup.

      Step 8 — Generating a Test Alert

      In this step, you will generate a test alert to ensure everything is connected. By default, Zabbix keeps track of the amount of free disk space on your server. It automatically detects all disk mounts and adds the corresponding checks. This discovery is executed every hour, so you need to wait a while for the notification to be triggered.

      Create a temporary file that's large enough to trigger Zabbix's file system usage alert. To do this, log in to your second Ubuntu server if you're not already connected.

      • ssh sammy@second_ubuntu_server_ip_address

      Next, determine how much free space you have on the server. You can use the df command to find out:

      The command df will report the disk space usage of your file system, and the -h will make the output human-readable. You'll see output like the following:

      Output

      Filesystem Size Used Avail Use% Mounted on /dev/vda1 25G 1.2G 23G 5% /

      In this case, the free space is 23GB. Your free space may differ.

      Use the fallocate command, which allows you to pre-allocate or de-allocate space to a file, to create a file that takes up more than 80% of the available disk space. This will be enough to trigger the alert:

      • fallocate -l 20G /tmp/temp.img

      After around an hour, Zabbix will trigger an alert about the amount of free disk space and will run the action you configured, sending the notification message. You can check your inbox for the message from the Zabbix server. You will see a message like:

      Output

      Problem started at 10:37:54 on 2019.04.05 Problem name: Free disk space is less than 20% on volume / Host: Second Ubuntu server Severity: Warning Original problem ID: 34

      You can also navigate to the Monitoring tab, and then Dashboard to see the notification and its details.

      Main dashboard

      Now that you know the alerts are working, delete the temporary file you created so you can reclaim your disk space:

      After a minute Zabbix will send the recovery message and the alert will disappear from main dashboard.

      Conclusion

      In this tutorial, you learned how to set up a simple and secure monitoring solution which will help you monitor the state of your servers. It can now warn you of problems, and you have the opportunity to analyze the processes occurring in your IT infrastructure.

      To learn more about setting up monitoring infrastructure, check out How To Install Elasticsearch, Logstash, and Kibana (Elastic Stack) on Ubuntu 18.04 and How To Gather Infrastructure Metrics with Metricbeat on Ubuntu 18.04.



      Source link

      How To Configure Multi-Factor Authentication on Ubuntu 18.04


      The author selected the Electronic Frontier Foundation to receive a donation as part of the Write for DOnations program.

      Introduction

      Two-factor authentication (2FA) is an authentication method that requires entering more than one piece of information to successfully log in to an account or device. In addition to entering a username and password combination, 2FA requires the user to enter an additional piece of information such as a one-time password (OTP), like a six-digit verification code.

      In general, 2FA requires the user to enter information of different types:

      • Something that the user knows, such as a password
      • Something that the user has, such as the verification code generated from an authenticator application

      2FA is a subset of multi-factor authentication (MFA), which, in addition to something that the user knows and something that they have, requires something that the user is. This is the case of biometrics, which use technologies such as fingerprint or voice recognition.

      2FA helps strengthen the authentication process to a certain service or device: even if the password were compromised, an attacker would also need to have access to the user’s device which holds the authenticator app used to generate the security codes. For this reason, many online services (including DigitalOcean) offer the possibility to enable 2FA for user accounts to increase account security when it comes to the authentication phase.

      In this guide, you will configure 2FA for a non-root sudoer user on an Ubuntu 18.04 installation with the Google PAM module. Since you’re configuring 2FA on the non-root user, you will still be able to access the machine from your root account in case of a lockout. The tutorial will be general enough to be applied both to server and to desktop installations, both local and remote.

      Prerequisites

      Before you begin this guide you’ll need the following:

      • One Ubuntu 18.04 server or desktop environment. If you are using an Ubuntu server, set it up by following the Ubuntu 18.04 initial server setup guide, including a non-root user with sudo privileges and a firewall.

      • An authenticator application installed on your mobile device, with which you can scan 2FA QR codes, such as Google Authenticator or Authy.

      Step 1 — Installing the Google PAM Module

      In order to configure 2FA on Ubuntu 18.04, you need to install Google’s PAM module for Linux. The Pluggable Authentication Module (PAM) is the authentication mechanism Linux uses. You will use Google’s PAM module to have your user authenticate over 2FA using Google-generated OTP codes.

      First, log in as the non-root user that you configured in the prerequisites:

      Update the Ubuntu repositories to download the latest version of the authenticator:

      Now that your repositories are up to date, install the latest version of the PAM module:

      • sudo apt-get install libpam-google-authenticator

      This is a very small package with no dependencies, so it will take a few seconds to install. In the next section, you will configure 2FA for the non-root user on the system.

      Step 2 — Configuring 2FA for a User

      Now that you've installed the PAM module, you will run it to generate a QR code for the logged in user. This will create the code, but the Ubuntu environment won't require 2FA until you've enabled it later in this tutorial.

      Run the google-authenticator command to start and configure the PAM module:

      The command will present a prompt that will ask you several configuration questions. The first question will ask if you want tokens to be time based. Time-based authentication tokens will expire after a set amount of time, which defaults to 30 seconds on most systems. Time-based tokens are more secure than tokens that are not time-based, and most 2FA implementations use them. You can choose either option here, but this tutorial will choose Yes to use time-based authentication tokens:

      Output

      Do you want authentication tokens to be time-based (y/n) y

      After answering y to this question, you will see several lines output to your console:

      • A QR code: This is the code you need to scan using your authenticator app. Once you have scanned it, it will immediately turn into a code-generating device that will create a new OTP every 30 seconds.
      • Your secret key: This is an alternative method to configure your authenticator app. If you are using an app that does not support QR scanning, you can enter the secret key to configure your authentication app.
      • Your verification code: This is the first six-digit verification code that this specific QR code generates.
      • Your emergency scratch codes: Also known as backup codes, these one-use tokens will allow you to pass 2FA authentication if you lose your authenticator device. Keep these codes in a safe place to avoid being locked out of the account.

      After you've configured your authenticator app and saved your backup codes in a safe place, the prompt will ask if you'd like to update the configuration file. If you choose n, you will need to run the configuration program again. You will enter y to save your changes and move forward:

      Output

      Do you want me to update your "~/.google_authenticator" file (y/n) y

      The next question will ask if you want to disallow authentication codes to be used more than once. By default, you can only use each code once, even if it remains valid for 30 seconds. This is the safest choice because it prevents replay attacks from an attacker who somehow managed to get a hold of your verification code after you have used it. For this reason, it's more secure to disallow codes to be used more than once. Answer y to disallow multiple uses of the same token:

      Output

      Do you want to disallow multiple uses of the same authentication token? This restricts you to one login about every 30s, but it increases your chances to notice or even prevent man-in-the-middle attacks (y/n) y

      The next question asks if you want authentication tokens to be accepted a short time before or after their normal validity time. Verification codes are very time-sensitive, which means that your tokens can be refused if your devices are not synchronized. This option allows you to work around this issue by extending the default validity time of verification codes so that, even if your devices were temporarily out of sync, your authentication codes would be accepted anyway. Making sure that the time is the same on all your devices is the best option, as choosing yes will decrease the security of your system. Answer n to this question to not allow a grace period:

      Output

      By default, tokens are good for 30 seconds and in order to compensate for possible time-skew between the client and the server, we allow an extra token before and after the current time. If you experience problems with poor time synchronization, you can increase the window from its default size of 1:30min to about 4min. Do you want to do so (y/n) n

      The last question asks if you want to enable rate limiting for log in attempts. This will not allow more than three failed log in attempts every 30 seconds, which is a good security strengthening technique. Enable it by answering y:

      Output

      If the computer that you are logging into isn't hardened against brute-force login attempts, you can enable rate-limiting for the authentication module. By default, this limits attackers to no more than 3 login attempts every 30s. Do you want to enable rate-limiting (y/n) y

      You have now configured and generated 2FA codes for the non-root user with the PAM module. Now that your codes are generated, you need to enable 2FA in your environment.

      Step 3 — Activating 2FA in Ubuntu

      The Google PAM module is now generating 2FA codes your user, but Ubuntu doesn't yet know that it needs to use the codes as part of the user's authentication process. In this step, you will update Ubuntu's configuration to require 2FA tokens in addition to the regular method of authentication.

      You have two different options at this point:

      • You can require 2FA every time a user logs in to the system and every time a user requests sudo privileges.
      • You can require 2FA only during log in, where subsequent sudo authentication attempts would only require the user password.

      The first option will be ideal for a shared environment, where you may want to protect any actions that require sudo permissions. The second approach is more practical for a local desktop environment, where you are the only user on the system.

      Note: If you are enabling 2FA on a remote machine that you access over SSH, like a DigitalOcean Droplet, you need to follow steps two and three from the How To Set Up Multi-Factor Authentication for SSH on Ubuntu 16.04 guide before proceeding with this tutorial. The remaining steps in this tutorial apply to all Ubuntu installations, but remote environments need additional updates to make the SSH service aware of 2FA.

      If you are not using SSH to access your Ubuntu installation, you can immediately proceed with the remaining steps in the tutorial.

      Requiring 2FA for Log In and sudo Requests

      To be prompted for 2FA during log in and subsequent privilege escalation requests, you need to edit the /etc/pam.d/common-auth file by adding a line to the end of the existing file.

      The common-auth file applies to all authentication mechanisms on the system, regardless of the desktop environment used. It also applies to authentication requests that happen after the user logs in to the system, such as during a sudo escalation request when installing a new package from the terminal.

      Open this file with the following command:

      • sudo nano /etc/pam.d/common-auth

      Add the highlighted line at the end of the file:

      /etc/pam.d/common-auth

      ...
      # and here are more per-package modules (the "Additional" block)
      session required    pam_unix.so
      session optional    pam_systemd.so
      # end of pam-auth-update config
      auth required pam_google_authenticator.so nullok
      

      This line tells the Ubuntu authentication system to require 2FA upon log in through the Google PAM module. The nullok option allows existing users to log into the system even if they haven't configured 2FA authentication for their account. In other words, users who have configured 2FA will be required to enter an authentication code at the next log in, while users who haven't run the google-authenticator command will be able to log in with only their username and password until they configure 2FA.

      Save and close the file after adding the line.

      Requiring 2FA for Log In Only

      If you want to only be prompted for 2FA when you first log in to the system on a desktop environment, you need to edit the configuration file for the desktop manager you are using. The name of the configuration file usually matches the name of the desktop environment. For example, the configuration file for gdm, the default Ubuntu desktop environment starting after Ubuntu 16.04, is /etc/pam.d/gdm.

      In the case of a headless server, such as a DigitalOcean Droplet, you will edit the /etc/pam.d/common-session file instead. Open the relevant file based on your environment:

      • sudo nano /etc/pam.d/common-session

      Add the highlighted line to the end of the file:

      /etc/pam.d/common-session

      #
      # /etc/pam.d/common-session - session-related modules common to all services
      #
      ...
      # # and here are more per-package modules (the "Additional" block)
      session required    pam_unix.so
      session optional    pam_systemd.so
      # end of pam-auth-update config
      auth required pam_google_authenticator.so nullok
      

      This will tell Ubuntu to require 2FA when a user connects to the system via the command line (either locally or remotely through SSH), but not during subsequent authentication attempts, such as sudo requests.

      You have now successfully configured Ubuntu to prompt you for 2FA either just during log in, or for every authenticated action performed on the system. You're now ready to test the configuration and make sure that you are prompted for 2FA when you log in to your Ubuntu installation.

      Step 4 — Testing 2FA

      In the previous step, you've configured 2FA to generate codes every 30 seconds. In this step, you will test 2FA by logging into your Ubuntu environment.

      First, log out and back in to your Ubuntu environment:

      ssh sammy@your_server_ip
      

      If you are using password-based authentication, you will be prompted for your user password:

      Output

      Password:

      Note: If you are testing this on a DigitalOcean Droplet or another remote server protected by certificate authentication, you won’t be prompted for a password, and your key will be passed and accepted automatically. You will therefore only be prompted for your verification code.

      Enter your password and you will be prompted for the 2FA verification code:

      Output

      Verification code:

      After entering your verification code, you will be logged in:

      Output

      sammy@your_server_ip: ~#

      If 2FA was only enabled for logins, you won’t be prompted for your 2FA codes again until the session expires or you log out manually.

      If you enabled 2FA through the common-auth file, you will be prompted for it on every login and request for sudo privileges:

      Output

      sammy@your_server_ip: ~# sudo -s
 sudo password for sammy:
 Verification code: 
root@your_server_ip:

      In this step you have confirmed that your 2FA configuration is working as expected. If you were not prompted for your verification codes in this phase, return to step three of the tutorial and confirm that you have edited the correct Ubuntu authentication file.

      Step 5 — Preventing a 2FA Lockout

      In the event of a lost or wiped phone, it is important to have proper backup methods in place to recover access to your 2FA-enabled account. When you configure 2FA for the first time, you have a few options to ensure that you can recover from a lock out:

      • Save a backup copy of your secret configuration codes in a safe place. You can do this manually, but some authentication apps like Authy provide backup code features.
      • Save your recovery codes in a safe place that can be accessed outside of your 2FA enabled environment.

      If for any reason you don't have access to your backup options, you can take additional steps to recover access to your 2FA enabled local environment or remote server.

      Step 6 — Recovering from a 2FA Lockout on a Local Environment (Optional)

      If you have physical access to the machine, you can boot into rescue mode to disable 2FA. Rescue mode is a target type (similar to a runlevel) in Linux that is used to preform administrative tasks. You will need to edit some settings in GRUB, which is the default boot loader in Ubuntu, to enter rescue mode.

      To access GRUB, you will first reboot your machine:

      When the GRUB menu appears, make sure the Ubuntu entry is highlighted. This is the default name on a 18.04 installation, but may be different if you manually changed it after installation.

      The default GRUB menu in Ubuntu 18.04

      Next, press the e key on your keyboard to edit the GRUB configuration before booting into your system.

      The GRUB configuration file in edit mode

      In the file that appears, scroll down until you see a line that starts with linux and ends with $vt_handoff. Go to the end of this line and append systemd.unit=rescue.target, making sure that you leave a space between $vt_handoff and systemd.unit=rescue.target. This will tell your Ubuntu machine to boot into rescue mode.

      Editing the GRUB Configuration File to Enable Maintenance Mode

      Once you have made the changes, save the file with the Ctrl+X keyboard combination. Your machine will reboot and you will find yourself at a command line. Press Enter to go into rescue mode.

      Command line maintenance mode prompt in Ubuntu 18.04

      Once in rescue mode, open the Google Authenticator configuration file. This will be located inside the locked-out user’s home directory:

      • nano /home/sammy/.google-authenticator

      The first line in this file is the user’s secret key, which is used to configure an authenticator app.

      You now have two choices:

      • You can copy the secret key and configure your authenticator app.
      • If you want to start from a clean slate, you can delete the ~/.google-authenticator file altogether to disable 2FA for this user. After logging in again as the non-root user, you can configure 2FA once again and get a brand new secret key.

      With either choice, you are able to recover from a 2FA lockout on a local environment by using the GRUB boot loader. In the next step, you will recover from a 2FA lockout on a remote environment.

      Step 7 — Recovering from a 2FA Lockout on a Remote Environment (Optional)

      If your non-root sudoer account is locked out on a remote machine, you can use the root user to temporarily disable 2FA or reconfigure 2FA.

      Start by logging in to your machine with the root user:

      Once logged in, open the Google Authenticator settings file that is located inside the locked-out user’s home directory:

      • sudo nano /home/sammy/.google_authenticator

      The first line in this file is the user’s secret key, which is what you need to configure an authenticator app.

      You now have two choices:

      • If you want to set up a new or wiped device, you can use the secret key to reconfigure your authenticator app.
      • If you want to start from a clean slate, you can delete the /home/sammy/.google_authenticator file altogether to disable 2FA for this user. After logging in as the non-root user, you can configure 2FA once again and get a brand new secret key.

      With either choice, you were able to recover from a 2FA lockout on a local environment by using the root user.

      Conclusion

      In this tutorial, you configured 2FA on an Ubuntu 18.04 machine. With 2FA configured on your environment, you have added an extra layer of protection to your account and you have made your system more secure. In addition to your traditional authentication method, you will also have to enter an additional verification code to log in. This makes it impossible for an attacker who managed to acquire your login credentials to be able to log in to your account without this additional verification code.



      Source link

      How To Install and Configure an Apache ZooKeeper Cluster on Ubuntu 18.04


      The author selected Wikimedia Foundation Inc. to receive a donation as part of the Write for DOnations program.

      Introduction

      Apache ZooKeeper is open-source software that enables resilient and highly reliable distributed coordination. It is commonly used in distributed systems to manage configuration information, naming services, distributed synchronization, quorum, and state. In addition, distributed systems rely on ZooKeeper to implement consensus, leader election, and group management.

      In this guide, you will install and configure Apache ZooKeeper 3.4.13 on Ubuntu 18.04. To achieve resilience and high availability, ZooKeeper is intended to be replicated over a set of hosts, called an ensemble. First, you will create a standalone installation of a single-node ZooKeeper server and then add in details for setting up a multi-node cluster. The standalone installation is useful in development and testing environments, but a cluster is the most practical solution for production environments.

      Prerequisites

      Before you begin this installation and configuration guide, you’ll need the following:

      • The standalone installation needs one Ubuntu 18.04 server with a minimum of 4GB of RAM set up by following the Ubuntu 18.04 initial server setup guide, including a non-root user with sudo privileges and a firewall. You need two additional servers, set up by following the same steps, for the multi-node cluster.
      • OpenJDK 8 installed on your server, as ZooKeeper requires Java to run. To do this, follow the “Install Specific Versions of OpenJDK” step from the How To Install Java with `apt` on Ubuntu 18.04 guide.

      Because ZooKeeper keeps data in memory to achieve high throughput and low latency, production systems work best with 8GB of RAM. Lower amounts of RAM may lead to JVM swapping, which could cause ZooKeeper server latency. High ZooKeeper server latency could result in issues like client session timeouts that would have an adverse impact on system functionality.

      Step 1 — Creating a User for ZooKeeper

      A dedicated user should run services that handle requests over a network and consume resources. This practice creates segregation and control that will improve your environment’s security and manageability. In this step, you’ll create a non-root sudo user, named zk in this tutorial, to run the ZooKeeper service.

      First, log in as the non-root sudo user that you created in the prerequisites.

      ssh sammy@your_server_ip
      

      Create the user that will run the ZooKeeper service:

      Passing the -m flag to the useradd command will create a home directory for this user. The home directory for zk will be /home/zk by default.

      Set bash as the default shell for the zk user:

      • sudo usermod --shell /bin/bash zk

      Set a password for this user:

      Next, you will add the zk user to the sudo group so it can run commands in a privileged mode:

      In terms of security, it is recommended that you allow SSH access to as few users as possible. Logging in remotely as sammy and then using su to switch to the desired user creates a level of separation between credentials for accessing the system and running processes. You will disable SSH access for both your zk and root user in this step.

      Open your sshd_config file:

      • sudo nano /etc/ssh/sshd_config

      Locate the PermitRootLogin line and set the value to no to disable SSH access for the root user:

      /etc/ssh/sshd_config

      PermitRootLogin no
      

      Under the PermitRootLogin value, add a DenyUsers line and set the value as any user who should have SSH access disabled:

      /etc/ssh/sshd_config

      DenyUsers zk
      

      Save and exit the file and then restart the SSH daemon to activate the changes.

      • sudo systemctl restart sshd

      Switch to the zk user:

      The -l flag invokes a login shell after switching users. A login shell resets environment variables and provides a clean start for the user.

      Enter the password at the prompt to authenticate the user.

      Now that you have created, configured, and logged in as the zk user, you will create a directory to store your ZooKeeper data.

      Step 2 — Creating a Data Directory for ZooKeeper

      ZooKeeper persists all configuration and state data to disk so it can survive a reboot. In this step, you will create a data directory that ZooKeeper will use to read and write data. You can create the data directory on the local filesystem or on a remote storage drive. This tutorial will focus on creating the data directory on your local filesystem.

      Create a directory for ZooKeeper to use:

      • sudo mkdir -p /data/zookeeper

      Grant your zk user ownership to the directory:

      • sudo chown zk:zk /data/zookeeper

      chown changes the ownership and group of the /data/zookeeper directory so that the user zk, who belongs to the group zk, owns the data directory.

      You have successfully created and configured the data directory. When you move on to configure ZooKeeper, you will specify this path as the data directory that ZooKeeper will use to store its files.

      Step 3 — Downloading and Extracting the ZooKeeper Binaries

      In this step, you will manually download and extract the ZooKeeper binaries to the /opt directory. You can use the Advanced Packaging Tool, apt, to download ZooKeeper, but it may install an older version with different features. Installing ZooKeeper manually will give you full control to choose which version you would like to use.

      Since you are downloading these files manually, start by changing to the /opt directory:

      From your local machine, navigate to the Apache download page. This page will automatically provide you with the mirror closest to you for the fastest download. Click the link to the suggested mirror site, then scroll down and click zookeeper/ to view the available releases. Select the version of ZooKeeper that you would like to install. This tutorial will focus on using 3.4.13. Once you select the version, right click the binary file ending with .tar.gz and copy the link address.

      From your server, use the wget command along with the copied link to download the ZooKeeper binaries:

      • sudo wget http://apache.osuosl.org/zookeeper/zookeeper-3.4.13/zookeeper-3.4.13.tar.gz

      Extract the binaries from the compressed archive:

      • sudo tar -xvf zookeeper-3.4.13.tar.gz

      The .tar.gz extension represents a combination of TAR packaging followed by a GNU zip (gzip) compression. You will notice that you passed the flag -xvf to the command to extract the archive. The flag x stands for extract, v enables verbose mode to show the extraction progress, and f allows specifying the input, in our case zookeeper-3.4.13.tar.gz, as opposed to STDIN.

      Next, give the zk user ownership of the extracted binaries so that it can run the executables. You can change ownership like so:

      • sudo chown zk:zk -R zookeeper-3.4.13

      Next, you will configure a symbolic link to ensure that your ZooKeeper directory will remain relevant across updates. You can also use symbolic links to shorten directory names, which can lessen the time it takes to set up your configuration files.

      Create a symbolic link using the ln command.

      • sudo ln -s zookeeper-3.4.13 zookeeper

      Change the ownership of that link to zk:zk. Notice that you have passed a -h flag to change the ownership of the link itself. Not specifying -h changes the ownership of the target of the link, which you explicitly did in the previous step.

      • sudo chown -h zk:zk zookeeper

      With the symbolic links created, your directory paths in the configurations will remain relevant and unchanged through future upgrades. You can now configure ZooKeeper.

      Step 4 — Configuring ZooKeeper

      Now that you've set up your environment, you are ready to configure ZooKeeper.

      The configuration file will live in the /opt/zookeeper/conf directory. This directory contains a sample configuration file that comes with the ZooKeeper distribution. This sample file, named zoo_sample.cfg, contains the most common configuration parameter definitions and sample values for these parameters. Some of the common parameters are as follows:

      • tickTime: Sets the length of a tick in milliseconds. A tick is a time unit used by ZooKeeper to measure the length between heartbeats. Minimum session timeouts are twice the tickTime.
      • dataDir: Specifies the directory used to store snapshots of the in-memory database and the transaction log for updates. You could choose to specify a separate directory for transaction logs.
      • clientPort: The port used to listen for client connections.
      • maxClientCnxns: Limits the maximum number of client connections.

      Create a configuration file named zoo.cfg at /opt/zookeeper/conf. You can create and open a file using nano or your favorite editor:

      • nano /opt/zookeeper/conf/zoo.cfg

      Add the following set of properties and values to that file:

      /opt/zookeeper/conf/zoo.cfg

      tickTime=2000
      dataDir=/data/zookeeper
      clientPort=2181
      maxClientCnxns=60
      

      A tickTime of 2000 milliseconds is the suggested interval between heartbeats. A shorter interval could lead to system overhead with limited benefits. The dataDir parameter points to the path defined by the symbolic link you created in the previous section. Conventionally, ZooKeeper uses port 2181 to listen for client connections. In most situations, 60 allowed client connections are plenty for development and testing.

      Save the file and exit the editor.

      You have configured ZooKeeper and are ready to start the server.

      Step 5 — Starting ZooKeeper and Testing the Standalone Installation

      You've configured all the components needed to run ZooKeeper. In this step, you will start the ZooKeeper service and test your configuration by connecting to the service locally.

      Navigate back to the /opt/zookeeper directory.

      Start ZooKeeper with the zkServer.sh command.

      You will see the following on your standard output:

      Output

      ZooKeeper JMX enabled by default Using config: /opt/zookeeper/bin/../conf/zoo.cfg Starting zookeeper ... STARTED

      Connect to the local ZooKeeper server with the following command:

      • bin/zkCli.sh -server 127.0.0.1:2181

      You will get a prompt with the label CONNECTED. This confirms that you have a successful local, standalone ZooKeeper installation. If you encounter errors, you will want to verify that the configuration is correct.

      Output

      Connecting to 127.0.0.1:2181 ... ... [zk: 127.0.0.1:2181(CONNECTED) 0]

      Type help on this prompt to get a list of commands that you can execute from the client. The output will be as follows:

      Output

      [zk: 127.0.0.1:2181(CONNECTED) 0] help ZooKeeper -server host:port cmd args stat path [watch] set path data [version] ls path [watch] delquota [-n|-b] path ls2 path [watch] setAcl path acl setquota -n|-b val path history redo cmdno printwatches on|off delete path [version] sync path listquota path rmr path get path [watch] create [-s] [-e] path data acl addauth scheme auth quit getAcl path close connect host:port

      After you've done some testing, you will close the client session by typing quit on the prompt. The ZooKeeper service will continue running after you closed the client session. Shut down the ZooKeeper service, as you'll configure it as a systemd service in the next step:

      You have now installed, configured, and tested a standalone ZooKeeper service. This setup is useful to familiarize yourself with ZooKeeper, but is also helpful for developmental and testing environments. Now that you know the configuration works, you will configure systemd to simplify the management of your ZooKeeper service.

      Step 6 — Creating and Using a Systemd Unit File

      The systemd, system and service manager, is an init system used to bootstrap the user space and to manage system processes after boot. You can create a daemon for starting and checking the status of ZooKeeper using systemd.

      Systemd Essentials is a great introductory resource for learning more about systemd and its constituent components.

      Use your editor to create a .service file named zk.service at /etc/systemd/system/.

      • sudo nano /etc/systemd/system/zk.service

      Add the following lines to the file to define the ZooKeeper Service:

      /etc/systemd/system/zk.service

      [Unit]
      Description=Zookeeper Daemon
      Documentation=http://zookeeper.apache.org
      Requires=network.target
      After=network.target
      
      [Service]    
      Type=forking
      WorkingDirectory=/opt/zookeeper
      User=zk
      Group=zk
      ExecStart=/opt/zookeeper/bin/zkServer.sh start /opt/zookeeper/conf/zoo.cfg
      ExecStop=/opt/zookeeper/bin/zkServer.sh stop /opt/zookeeper/conf/zoo.cfg
      ExecReload=/opt/zookeeper/bin/zkServer.sh restart /opt/zookeeper/conf/zoo.cfg
      TimeoutSec=30
      Restart=on-failure
      
      [Install]
      WantedBy=default.target
      

      The Service section in the unit file configuration specifies the working directory, the user under which the service would run, and the executable commands to start, stop, and restart the ZooKeeper service. For additional information on all the unit file configuration options, you can read the Understanding Systemd Units and Unit Files article.

      Save the file and exit the editor.

      Now that your systemd configuration is in place, you can start the service:

      Once you've confirmed that your systemd file can successfully start the service, you will enable the service to start on boot.

      This output confirms the creation of the symbolic link:

      Output

      Created symlink /etc/systemd/system/multi-user.target.wants/zk.service → /etc/systemd/system/zk.service.

      Check the status of the ZooKeeper service using:

      Stop the ZooKeeper service using systemctl.

      Finally, to restart the daemon, use the following command:

      • sudo systemctl restart zk

      The systemd mechanism is becoming the init system of choice on many Linux distributions. Now that you've configured systemd to manage ZooKeeper, you can leverage this fast and flexible init model to start, stop, and restart the ZooKeeper service.

      Step 7 — Configuring a Multi-Node ZooKeeper Cluster

      While the standalone ZooKeeper server is useful for development and testing, every production environment should have a replicated multi-node cluster.

      Nodes in the ZooKeeper cluster that work together as an application form a quorum. Quorum refers to the minimum number of nodes that need to agree on a transaction before it's committed. A quorum needs an odd number of nodes so that it can establish a majority. An even number of nodes may result in a tie, which would mean the nodes would not reach a majority or consensus.

      In a production environment, you should run each ZooKeeper node on a separate host. This prevents service disruption due to host hardware failure or reboots. This is an important and necessary architectural consideration for building a resilient and highly available distributed system.

      In this tutorial, you will install and configure three nodes in the quorum to demonstrate a multi-node setup. Before you configure a three-node cluster, you will spin up two additional servers with the same configuration as your standalone ZooKeeper installation. Ensure that the two additional nodes meet the prerequisites, and then follow steps one through six to set up a running ZooKeeper instance.

      Once you've followed steps one through six for the new nodes, open zoo.cfg in the editor on each node.

      • sudo nano /opt/zookeeper/conf/zoo.cfg

      All nodes in a quorum will need the same configuration file. In your zoo.cfg file on each of the three nodes, add the additional configuration parameters and values for initLimit, syncLimit, and the servers in the quorum, at the end of the file.

      /opt/zookeeper/conf/zoo.cfg

      tickTime=2000
      dataDir=/data/zookeeper
      clientPort=2181
      maxClientCnxns=60
      initLimit=10
      syncLimit=5
      server.1=your_zookeeper_node_1:2888:3888
      server.2=your_zookeeper_node_2:2888:3888
      server.3=your_zookeeper_node_3:2888:3888
      

      initLimit specifies the time that the initial synchronization phase can take. This is the time within which each of the nodes in the quorum needs to connect to the leader. syncLimit specifies the time that can pass between sending a request and receiving an acknowledgment. This is the maximum time nodes can be out of sync from the leader. ZooKeeper nodes use a pair of ports, :2888 and :3888, for follower nodes to connect to the leader node and for leader election, respectively.

      Once you've updated the file on each node, you will save and exit the editor.

      To complete your multi-node configuration, you will specify a node ID on each of the servers. To do this, you will create a myid file on each node. Each file will contain a number that correlates to the server number assigned in the configuration file.

      On your_zookeeper_node_1, create the myid file that will specify the node ID:

      • sudo nano /data/zookeeper/myid

      Since your_zookeeper_node_1 is identified as server.1, you will enter 1 to define the node ID. After adding the value, your file will look like this:

      your_zookeeper_node_1 /data/zookeeper/myid

      1

      Follow the same steps for the remaining nodes. The myid file on each node should be as follows:

      your_zookeeper_node_1 /data/zookeeper/myid

      1

      your_zookeeper_node_2 /data/zookeeper/myid

      2

      your_zookeeper_node_3 /data/zookeeper/myid

      3

      You have now configured a three-node ZooKeeper cluster. Next, you will run the cluster and test your installation.

      Step 8 — Running and Testing the Multi-Node Installation

      With each node configured to work as a cluster, you are ready to start a quorum. In this step, you will start the quorum on each node and then test your cluster by creating sample data in ZooKeeper.

      To start a quorum node, first change to the /opt/zookeeper directory on each node:

      Start each node with the following command:

      • java -cp zookeeper-3.4.13.jar:lib/log4j-1.2.17.jar:lib/slf4j-log4j12-1.7.25.jar:lib/slf4j-api-1.7.25.jar:conf org.apache.zookeeper.server.quorum.QuorumPeerMain conf/zoo.cfg

      As nodes start up, you will intermittently see some connection errors followed by a stage where they join the quorum and elect a leader among themselves. After a few seconds of initialization, you can start testing your installation.

      Log in via SSH to your_zookeeper_node_3 as the non-root user you configured in the prerequisites:

      • ssh sammy@your_zookeeper_node_3

      Once logged in, switch to your zk user:

      your_zookeeper_node_3 /data/zookeeper/myid

      Enter the password for the zk user. Once logged in, change the directory to /opt/zookeeper:

      your_zookeeper_node_3 /data/zookeeper/myid

      You will now start a ZooKeeper command line client and connect to ZooKeeper on your_zookeeper_node_1:

      your_zookeeper_node_3 /data/zookeeper/myid

      • bin/zkCli.sh -server your_zookeeper_node_1:2181

      In the standalone installation, both the client and server were running on the same host. This allowed you to establish a client connection with the ZooKeeper server using localhost. Since the client and server are running on different nodes in your multi-node cluster, in the previous step you needed to specify the IP address of your_zookeeper_node_1 to connect to it.

      You will see the familiar prompt with the CONNECTED label, similar to what you saw in Step 5.

      Next, you will create, list, and then delete a znode. The znodes are the fundamental abstractions in ZooKeeper that are analogous to files and directories on a file system. ZooKeeper maintains its data in a hierarchical namespace, and znodes are the data registers of this namespace.

      Testing that you can successfully create, list, and then delete a znode is essential to establishing that your ZooKeeper cluster is installed and configured correctly.

      Create a znode named zk_znode_1 and associate the string sample_data with it.

      • create /zk_znode_1 sample_data

      You will see the following output once created:

      Output

      Created /zk_znode_1

      List the newly created znode:

      Get the data associated with it:

      ZooKeeper will respond like so:

      Output

      [zk: your_zookeeper_node_1:2181(CONNECTED)] ls / [zk_znode_1, zookeeper] [zk: your_zookeeper_node_1:2181(CONNECTED)] get /zk_znode_1 sample_data cZxid = 0x100000002 ctime = Tue Nov 06 19:47:41 UTC 2018 mZxid = 0x100000002 mtime = Tue Nov 06 19:47:41 UTC 2018 pZxid = 0x100000002 cversion = 0 dataVersion = 0 aclVersion = 0 ephemeralOwner = 0x0 dataLength = 11 numChildren = 0

      The output confirms the value, sample_data, that you associated with zk_node_1. ZooKeeper also provides additional information about creation time, ctime, and modification time, mtime. ZooKeeper is a versioned data store, so it also presents you with metadata about the data version.

      Delete the zk_znode_1 znode:

      In this step, you successfully tested connectivity between two of your ZooKeeper nodes. You also learned basic znode management by creating, listing, and deleting znodes. Your multi-node configuration is complete, and you are ready to start using ZooKeeper.

      Conclusion

      In this tutorial, you configured and tested both a standalone and multi-node ZooKeeper environment. Now that your multi-node ZooKeeper deployment is ready to use, you can review the official ZooKeeper documentation for additional information and projects.



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