Convert site to Hugo (#8316)
This commit converts content and layout to use Hugo.
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Bjørn Erik Pedersen
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---
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title: Connect a Front End to a Back End Using a Service
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content_template: templates/tutorial
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---
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{{% capture overview %}}
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This task shows how to create a frontend and a backend
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microservice. The backend microservice is a hello greeter. The
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frontend and backend are connected using a Kubernetes Service object.
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{{% /capture %}}
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{{% capture objectives %}}
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* Create and run a microservice using a Deployment object.
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* Route traffic to the backend using a frontend.
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* Use a Service object to connect the frontend application to the
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backend application.
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{{% /capture %}}
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{{% capture prerequisites %}}
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* {{< include "task-tutorial-prereqs.md" >}} {{< version-check >}}
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* This task uses
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[Services with external load balancers](/docs/tasks/access-application-cluster/create-external-load-balancer/), which
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require a supported environment. If your environment does not
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support this, you can use a Service of type
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[NodePort](/docs/concepts/services-networking/service/#type-nodeport) instead.
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{{% /capture %}}
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{{% capture lessoncontent %}}
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### Creating the backend using a Deployment
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The backend is a simple hello greeter microservice. Here is the configuration
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file for the backend Deployment:
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{{< code file="hello.yaml" >}}
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Create the backend Deployment:
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```
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kubectl create -f https://k8s.io/docs/tasks/access-application-cluster/hello.yaml
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```
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View information about the backend Deployment:
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```
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kubectl describe deployment hello
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```
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The output is similar to this:
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```
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Name: hello
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Namespace: default
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CreationTimestamp: Mon, 24 Oct 2016 14:21:02 -0700
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Labels: app=hello
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tier=backend
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track=stable
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Annotations: deployment.kubernetes.io/revision=1
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Selector: app=hello,tier=backend,track=stable
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Replicas: 7 desired | 7 updated | 7 total | 7 available | 0 unavailable
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StrategyType: RollingUpdate
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MinReadySeconds: 0
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RollingUpdateStrategy: 1 max unavailable, 1 max surge
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Pod Template:
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Labels: app=hello
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tier=backend
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track=stable
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Containers:
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hello:
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Image: "gcr.io/google-samples/hello-go-gke:1.0"
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Port: 80/TCP
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Environment: <none>
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Mounts: <none>
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Volumes: <none>
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Conditions:
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Type Status Reason
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---- ------ ------
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Available True MinimumReplicasAvailable
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Progressing True NewReplicaSetAvailable
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OldReplicaSets: <none>
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NewReplicaSet: hello-3621623197 (7/7 replicas created)
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Events:
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...
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```
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### Creating the backend Service object
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The key to connecting a frontend to a backend is the backend
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Service. A Service creates a persistent IP address and DNS name entry
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so that the backend microservice can always be reached. A Service uses
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selector labels to find the Pods that it routes traffic to.
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First, explore the Service configuration file:
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{{< code file="hello-service.yaml" >}}
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In the configuration file, you can see that the Service routes traffic to Pods
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that have the labels `app: hello` and `tier: backend`.
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Create the `hello` Service:
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```
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kubectl create -f https://k8s.io/docs/tasks/access-application-cluster/hello-service.yaml
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```
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At this point, you have a backend Deployment running, and you have a
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Service that can route traffic to it.
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### Creating the frontend
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Now that you have your backend, you can create a frontend that connects to the backend.
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The frontend connects to the backend worker Pods by using the DNS name
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given to the backend Service. The DNS name is "hello", which is the value
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of the `name` field in the preceding Service configuration file.
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The Pods in the frontend Deployment run an nginx image that is configured
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to find the hello backend Service. Here is the nginx configuration file:
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{{< code file="frontend/frontend.conf" >}}
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Similar to the backend, the frontend has a Deployment and a Service. The
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configuration for the Service has `type: LoadBalancer`, which means that
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the Service uses the default load balancer of your cloud provider.
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{{< code file="frontend.yaml" >}}
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Create the frontend Deployment and Service:
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```
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kubectl create -f https://k8s.io/docs/tasks/access-application-cluster/frontend.yaml
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```
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The output verifies that both resources were created:
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```
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deployment "frontend" created
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service "frontend" created
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```
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**Note**: The nginx configuration is baked into the
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[container image](/docs/tasks/access-application-cluster/frontend/Dockerfile).
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A better way to do this would be to use a
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[ConfigMap](/docs/tasks/configure-pod-container/configure-pod-configmap/), so
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that you can change the configuration more easily.
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### Interact with the frontend Service
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Once you’ve created a Service of type LoadBalancer, you can use this
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command to find the external IP:
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```
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kubectl get service frontend
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```
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The external IP field may take some time to populate. If this is the
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case, the external IP is listed as `<pending>`.
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```
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NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
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frontend 10.51.252.116 <pending> 80/TCP 10s
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```
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Repeat the same command again until it shows an external IP address:
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```
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NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
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frontend 10.51.252.116 XXX.XXX.XXX.XXX 80/TCP 1m
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```
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### Send traffic through the frontend
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The frontend and backends are now connected. You can hit the endpoint
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by using the curl command on the external IP of your frontend Service.
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```
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curl http://<EXTERNAL-IP>
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```
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The output shows the message generated by the backend:
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```
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{"message":"Hello"}
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```
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{{% /capture %}}
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{{% capture whatsnext %}}
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* Learn more about [Services](/docs/concepts/services-networking/service/)
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* Learn more about [ConfigMaps](/docs/tasks/configure-pod-container/configure-pod-configmap/)
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{{% /capture %}}
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