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      How To Create an API Gateway Using Ambassador on DigitalOcean Kubernetes


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

      Introduction

      Ambassador is an API Gateway for cloud-native applications that routes traffic between heterogeneous services and maintains decentralized workflows. It acts as a single entry point and supports tasks like service discovery, configuration management, routing rules, and rate limiting. It provides great flexibility and ease of configuration for your services.

      Envoy is an open source service proxy designed for cloud-native applications. In Kubernetes, Ambassador can be used to install and manage Envoy configuration. Ambassador supports zero downtime configuration changes and integration with other features like authentication, service discovery, and services meshes.

      In this tutorial, you’ll set up an Ambassador API Gateway on a Kubernetes cluster using Helm and configure it for routing incoming traffic to various services based on routing rules. You’ll configure these rules to route the traffic based on hostname or path to the relevant services.

      Prerequisites

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

      Step 1 — Installing Ambassador

      In this section, you will install Ambassador on your Kubernetes cluster. Ambassador can be installed using a Helm chart or by passing a YAML configuration file to the kubectl command.

      Note: DigitalOcean Kubernetes has RBAC enabled by default, so when using a YAML configuration file for installation you need to ensure that you use the RBAC enabled one. You can find further details about deploying Amabassador to Kubernetes via YAML in Ambassador’s documentation.

      For the purposes of this tutorial, you’ll use a Helm chart to install Ambassador to your cluster. Having followed the prerequisites, you’ll have Helm installed to your cluster.

      To begin, run the following command to install Ambassador via Helm:

      • helm upgrade --install --wait ambassador stable/ambassador

      You’ll see output similar to the following:

      Output

      Release "ambassador" does not exist. Installing it now. NAME: ambassador LAST DEPLOYED: Tue Jun 18 02:15:00 2019 NAMESPACE: default STATUS: DEPLOYED RESOURCES: ==> v1/Deployment NAME READY UP-TO-DATE AVAILABLE AGE ambassador 3/3 3 3 2m39s ==> v1/Pod(related) NAME READY STATUS RESTARTS AGE ambassador-7d55c468cb-4gpq9 1/1 Running 0 2m38s ambassador-7d55c468cb-jr9zr 1/1 Running 0 2m38s ambassador-7d55c468cb-zhm7l 1/1 Running 0 2m38s ==> v1/Service NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE ambassador LoadBalancer 10.245.183.114 139.59.52.164 80:30001/TCP,443:31557/TCP 2m40s ambassador-admins ClusterIP 10.245.46.43 <none> 8877/TCP 2m41s ==> v1/ServiceAccount NAME SECRETS AGE ambassador 1 2m43s ==> v1beta1/ClusterRole NAME AGE ambassador 2m41s ==> v1beta1/ClusterRoleBinding NAME AGE ambassador 2m41s ==> v1beta1/CustomResourceDefinition NAME AGE authservices.getambassador.io 2m42s consulresolvers.getambassador.io 2m41s kubernetesendpointresolvers.getambassador.io 2m42s kubernetesserviceresolvers.getambassador.io 2m43s mappings.getambassador.io 2m41s modules.getambassador.io 2m41s ratelimitservices.getambassador.io 2m42s tcpmappings.getambassador.io 2m41s tlscontexts.getambassador.io 2m42s tracingservices.getambassador.io 2m43s . . .

      This will create an Ambassador deployment, service, and a Load Balancer with your Kubernetes cluster nodes attached. You’ll need the Load Balancer’s IP to map it to your domain’s A records.

      To get the IP address of your Ambassador Load Balancer, run the following:

      • kubectl get svc --namespace default ambassador

      You’ll see output similar to:

      Output

      NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE ambassador LoadBalancer your_cluster_IP your-IP-address 80:30001/TCP,443:31557/TCP 8m4s

      Note the external IP your-IP-address in this step and map the domains (via your domain provider) svc1.your-domain, svc2.your-domain, and svc3.your-domain to point to this IP address.

      You can enable HTTPS with your DigitalOcean Load Balancer using the steps given at How to Configure SSL Termination. It is recommended to configure TLS termination via the Load Balancer. Another way of configuring TLS termination is using Ambassador’s TLS Support

      You’ve installed Ambassador on your Kubernetes cluster using Helm which created an Ambassador deployment with three replicas in the default namespace. This also created a Load Balancer with a public IP to route all traffic toward the API Gateway. Next you’ll create Kubernetes deployments for three different services that you’ll be using to test this API Gateway.

      Step 2 — Setting Up Web Server Deployments

      In this section, you’ll create three deployments to run three different web server containers. You’ll create YAML files with definitions of Kubernetes deployments for the three different web server containers and deploy them using kubectl.

      Open your preferred text editor to create your first deployment for an Nginx web server:

      Enter the following yaml configuration in your file:

      svc1-deploy.yaml

      apiVersion: extensions/v1beta1
      kind: Deployment
      metadata:
        name: svc1
      spec:
        replicas: 1
        selector:
          matchLabels:
            app: nginx
            name: svc1
        strategy:
          type: RollingUpdate
        template:
          metadata:
            labels:
              app: nginx
              name: svc1
          spec:
            containers:
            - name: nginx
              image: nginx:latest
              ports:
              - name: http
                containerPort: 80
      

      Here you have defined a Kubernetes Deployment with the nginx:latest container image to be deployed with 1 replica, called svc1. The Deployment is defined to expose in-cluster at port 80.

      Save and close the file.

      Then run the following command to apply this configuration:

      • kubectl apply -f svc1-deploy.yaml

      You’ll see output confirming creation:

      Output

      deployment.extensions/svc1 created

      Now, create a second web server deployment. Open a file called svc2-deploy.yaml with:

      Enter the following YAML configuration in the file:

      svc2-deploy.yaml

      apiVersion: extensions/v1beta1
      kind: Deployment
      metadata:
        name: svc2
      spec:
        replicas: 1
        selector:
          matchLabels:
            app: httpd
            name: svc2
        strategy:
          type: RollingUpdate
        template:
          metadata:
            labels:
              app: httpd
              name: svc2
          spec:
            containers:
            - name: httpd
              image: httpd:latest
              ports:
              - name: http
                containerPort: 80
      

      Here you have defined a Kubernetes Deployment with the httpd container image to be deployed with 1 replica, called svc2.

      Save and close the file.

      Run the following command to apply this configuration:

      • kubectl apply -f svc2-deploy.yaml

      You’ll see this output:

      Output

      deployment.extensions/svc2 created

      Finally for the third deployment, open and create the svc3-deploy.yaml file:

      Add the following lines to the file:

      svc3-deploy.yaml

      apiVersion: extensions/v1beta1
      kind: Deployment
      metadata:
        name: svc3
      spec:
        replicas: 1
        selector:
          matchLabels:
            app: httpbin
            name: svc3
        strategy:
          type: RollingUpdate
        template:
          metadata:
            labels:
              app: httpbin
              name: svc3
          spec:
            containers:
            - name: httpbin
              image: kennethreitz/httpbin:latest
              ports:
              - name: http
                containerPort: 80
      

      Here you have defined a Kubernetes Deployment with the httpbin container image to be deployed with 1 replica, called svc3.

      Save and close the file.

      Finally, run the following command to apply:

      • kubectl apply -f svc3-deploy.yaml

      And you’ll see the following output:

      Output

      deployment.extensions/svc3 created

      You’ve deployed three web server containers using Kubernetes deployments. In the next step, you will be exposing these deployments to internet traffic.

      Step 3 — Exposing Apps Using Services with Ambassador Annotations

      In this section, you will expose your web apps to the internet creating Kubernetes Services with Ambassador annotations to configure rules to route traffic to them. Annotations in Kubernetes are a way to add metadata to objects. Ambassador uses these annotation values from services to configure its routing rules.

      As a reminder you need to have your domains (for example: svc1.your-domain, svc2.your-domain, and svc3.your-domain) mapped to the Load Balancer’s public IP in your DNS records.

      Define a Kubernetes service for the svc1 deployment with Ambassador annotations by creating and opening this file:

      Note: The mapping name should be unique for every Ambassador annotation block. The mapping acts as an identifier for every annotation block and if repeated it will overlap the older annotation block.

      svc1-service.yaml

      apiVersion: v1
      kind: Service
      metadata:
        name: svc1
        annotations:
          getambassador.io/config: |
            ---
            apiVersion: ambassador/v1
            kind: Mapping
            name: svc1-service_mapping
            host: svc1.your-domain
            prefix: /
            service: svc1:80
      spec:
        selector:
          app: nginx
          name: svc1
        ports:
        - name: http
          protocol: TCP
          port: 80
      

      In this YAML code, you have defined a Kubernetes service svc1 with Ambassador annotations to map hostname svc1.your-domain to this service.

      Save and exit svc1-service.yaml, and then execute the following to apply this configuration:

      • kubectl apply -f svc1-service.yaml

      You’ll see this output:

      Output

      service/svc1 created

      Create your second Kubernetes service for svc2 deployment with Ambassador annotations. This is another example of host-based routing with Ambassador:

      Add the following configuration to the file:

      svc2-service.yaml

      apiVersion: v1
      kind: Service
      metadata:
        name: svc2
        annotations:
          getambassador.io/config: |
            ---
            apiVersion: ambassador/v1
            kind: Mapping
            name: svc2-service_mapping
            host: svc2.your-domain
            prefix: /
            service: svc2:80
      spec:
        selector:
          app: httpd
          name: svc2
        ports:
        - name: http
          protocol: TCP
          port: 80
      

      Save this as svc2-service.yaml. Here, you’ve defined another Kubernetes service with Ambassador annotations to route traffic to svc2 when any request is received by Ambassador with the host header value as svc2.your-domain. Therefore this host-based routing will allow you to send a request to the subdomain svc2.your-domain, which will route the traffic to the service svc2 and serve your request from httpd web server.

      To create this service, execute the following:

      • kubectl apply -f svc2-service.yaml

      You’ll see the following output:

      Output

      service/svc2 created

      Create a third Kubernetes service for your svc3 deployment and serve it via the path svc2.your-domain/bin. This will configure path-based routing for Ambassador:

      svc3-service.yaml

      apiVersion: v1
      kind: Service
      metadata:
        name: svc3
      spec:
        selector:
          app: httpbin
          name: svc3
        ports:
        - name: http
          protocol: TCP
          port: 80
      

      Save this as svc3-service.yaml and run the following to apply the configuration:

      • kubectl apply -f svc3-service.yaml

      Your output will be:

      Output

      service/svc3 created

      Edit svc2-service.yaml to append the second Ambassador annotation block to route /bin to svc3 service:

      svc2-service.yaml

      apiVersion: v1
      kind: Service
      metadata:
        name: svc2
        annotations:
          getambassador.io/config: |
            ---
            apiVersion: ambassador/v1
            kind: Mapping
            name: svc2-service_mapping
            host: svc2.your-domain
            prefix: /
            service: svc2:80
            ---
            apiVersion: ambassador/v1
            kind: Mapping
            name: svc3-service_mapping
            host: svc2.your-domain
            prefix: /bin
            service: svc3:80
      spec:
        selector:
          app: httpd
          name: svc2
        ports:
        - name: http
          protocol: TCP
          port: 80
      

      You’ve added the second Ambassador annotation block to configure paths beginning with /bin to map to your svc3 Kubernetes service. In order to route requests for svc2.your-domain/bin to svc3, you have added the second annotation block here as the host value svc2.your-domain, which is the same for both of the blocks. Therefore path-based routing will allow you to send a request to svc2.your-domain/bin, which will be received by service svc3 and served by the httpbin application in this tutorial

      Now run the following to apply the changes:

      • kubectl apply -f svc2-service.yaml

      You’ll see this output:

      Output

      service/svc2 configured

      You have created Kubernetes Services for the three deployments and added host-based and path-based routing rules with Ambassador annotations. Next, you’ll add advanced configuration to these services to configure routing, redirection, and custom headers.

      Step 4 — Advanced Ambassador Configurations for Routing

      In this section, you will configure the services with further Ambassador annotations to modify headers and configure redirection.

      curl the domain svc1.your-domain and check the response headers:

      Your output will be similar to the following:

      Output

      HTTP/1.1 200 OK server: envoy date: Mon, 17 Jun 2019 21:41:00 GMT content-type: text/html content-length: 612 last-modified: Tue, 21 May 2019 14:23:57 GMT etag: "5ce409fd-264" accept-ranges: bytes x-envoy-upstream-service-time: 0

      This output shows the headers received from the service routed using Ambassador. You’ll add custom headers to your service response using Ambassador annotations and validate the output for new added headers.

      To add custom headers to your service response, remove the header x-envoy-upstream-service-time from the response and add a new response header x-geo-location: India for svc1. (You may change this header as per your requirements.)

      Edit the file svc1-service.yaml:

      Update the annotation with the following highlighted lines:

      svc1-service.yaml

      apiVersion: v1
      kind: Service
      metadata:
        name: svc1
        annotations:
          getambassador.io/config: |
            ---
            apiVersion: ambassador/v1
            kind: Mapping
            name: svc1-service_mapping
            host: svc1.example.com
            prefix: /
            remove_response_headers:
            - x-envoy-upstream-service-time
            add_response_headers:
              x-geo-location: India
            service: svc1:80
      spec:
        selector:
          app: nginx
          name: svc1
        ports:
        - name: http
          protocol: TCP
          port: 80
      

      Here you have modified the svc1 service to remove x-envoy-upstream-service-time and added the x-geo-location: India header in the HTTP response.

      Apply the changes you have made:

      • kubectl apply -f svc1-service.yaml

      You will see the following output:

      Output

      service/svc1 configured

      Now run curl to validate the updated headers in the service response:

      The output will be similar to this:

      Output

      HTTP/1.1 200 OK server: envoy date: Mon, 17 Jun 2019 21:45:26 GMT content-type: text/html content-length: 612 last-modified: Tue, 21 May 2019 14:23:57 GMT etag: "5ce409fd-264" accept-ranges: bytes x-geo-location: India

      Now edit svc3-service.yaml to redirect requests for your hostname svc3.your-domain to path svc2.your-domain/bin:

      Append the Ambassador annotation block as shown in the following YAML and save it:

      svc3-service.yaml

      apiVersion: v1
      kind: Service
      metadata:
        name: svc3
        annotations:
          getambassador.io/config: |
            ---
            apiVersion: ambassador/v1
            kind:  Mapping
            name:  redirect_mapping
            host: svc3.your-domain
            prefix: /
            service: svc2.your-domain
            host_redirect: true
            path_redirect: /bin
      spec:
        selector:
          app: httpbin
          name: svc3
        ports:
        - name: http
          protocol: TCP
          port: 80
      

      You’ve added host_redirect: true to configure a 301 redirection response for svc3 to svc2.your-domain/bin for hostname svc3.your-domain. The host_redirect parameter sends a 301 redirection response to the client. If not set, the requests will receive 200 HTTP responses rather than 301 HTTP responses.

      Now run the following command to apply these changes:

      • kubectl apply -f svc3-service.yaml

      You will see similar output to:

      Output

      service/svc3 configured

      You can now check the response for svc3.your-domain using curl:

      Your output will be similar to the following:

      Output

      HTTP/1.1 301 Moved Permanently location: http://svc2.your-domain/bin date: Mon, 17 Jun 2019 21:52:05 GMT server: envoy transfer-encoding: chunked

      The output is a HTTP header for the request’s response to the service svc3.your-domainshowing that the configuration of host_redirect: true in your service annotation has correctly provided the HTTP status code: 301 Moved Permanently.

      You’ve configured the service with Ambassador annotations to modify HTTP headers and configure redirections. Next you will be adding global configuration to the Ambassador API Gateway service.

      Step 5 — Setting Up Ambassador Global Configurations

      In this section, you will edit the Ambassador service to add global GZIP compression configuration. GZIP compression will compress the HTTP assets size and reduce network bandwidth requirements leading to faster response times for the web clients. This configuration affects all the traffic being routed out through the Ambassador API Gateway. Similarly, you can configure other global modules with Ambassador, which let you enable special behaviors for Ambassador at a global level. These global configurations can be applied using annotations to the Ambassador service. You can refer to Ambassador’s Global Configuration documentation for further information.

      The following kubectl edit command will open the default editor, which is vim. To use nano, for example, you can set the environment variable KUBE_EDITOR to nano:

      • export KUBE_EDITOR="nano"

      Edit the Ambassador service:

      • kubectl edit service ambassador

      Now add the highlighted lines to a new annotation block for GZIP compression:

      Editing Ambassador Service

      apiVersion: v1
      kind: Service
      metadata:
        annotations:
          getambassador.io/config: |
            ---
            apiVersion: ambassador/v1
            kind: Module
            name: ambassador
            config:
              service_port: 8080
            ---
            apiVersion: ambassador/v0
            kind:  Module
            name:  ambassador
            config:
              gzip:
                memory_level: 5
                min_content_length: 256
                compression_level: BEST
                compression_strategy: DEFAULT
                content_type:
                - application/javascript
                - application/json
                - text/html
                - text/plain
                disable_on_etag_header: false
                remove_accept_encoding_header: false
        creationTimestamp: "2019-06-17T20:45:04Z"
        labels:
          app.kubernetes.io/instance: ambassador
          app.kubernetes.io/managed-by: Tiller
          app.kubernetes.io/name: ambassador
          helm.sh/chart: ambassador-2.8.2
        name: ambassador
        namespace: default
        resourceVersion: "2153"
        . . .
      

      You’ve added the Ambassador annotation block to your Ambassador service and configured GZIP globally for the API Gateway. Here you have included configuration to control the amount of internal memory used with memory_level, which can be a value from 1 to 9. The compression_level set at BEST ensures a higher compression rate at the cost of higher latency. With min_content_length you have configured the minimum response length to 256 bytes. For content_type you’ve specifically included a set of media types (formerly MIME-types) that yield compression. Finally you added the final two configurations as false to allow for compression.

      You can read more about GZIP compression on Envoy’s GZIP page.

      Any changes in this service apply as global configurations for the API Gateway.

      Once you have exited the editor you’ll see output similar to the following:

      Output

      service/ambassador edited

      Check svc1.your-domain using curl for the content-encoding header having value gzip:

      • curl --compressed -i http://svc1.example.com

      The output will be similar to this:

      Output

      HTTP/1.1 200 OK server: envoy date: Mon, 17 Jun 2019 22:25:35 GMT content-type: text/html last-modified: Tue, 21 May 2019 14:23:57 GMT accept-ranges: bytes x-geo-location: India vary: Accept-Encoding content-encoding: gzip transfer-encoding: chunked <!DOCTYPE html> <html> <head> <title>Welcome to nginx!</title> <style> body { width: 35em; margin: 0 auto; font-family: Tahoma, Verdana, Arial, sans-serif; } </style> </head> <body> <h1>Welcome to nginx!</h1> <p>If you see this page, the nginx web server is successfully installed and working. Further configuration is required.</p> <p>For online documentation and support please refer to <a href="http://nginx.org/">nginx.org</a>.<br/> Commercial support is available at <a href="http://nginx.com/">nginx.com</a>.</p> <p><em>Thank you for using nginx.</em></p> </body> </html>

      Here you can see the default HTML page of Nginx with its response header showing that content-encoding of the received response is gzip compressed.

      You’ve added global configuration to Ambassador to enable GZIP configuration for selected content type responses across the API Gateway.

      Conclusion

      You have successfully set up an API Gateway for your Kubernetes cluster using Ambassador. You are now able to expose your apps using host- and path-based routing, custom headers, and global GZIP compression.

      For further information about the Ambassador annotations and configuration parameters, read Ambassador’s official documentation.



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