This task shows how to create a frontend and a backend microservice. The backend microservice is a hello greeter. The frontend and backend are connected using a Kubernetes Service object.
You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:
The backend is a simple hello greeter microservice. Here is the configuration file for the backend Deployment:
Create the backend Deployment:
kubectl create -f https://k8s.io/docs/tasks/access-application-cluster/hello.yaml
View information about the backend Deployment:
kubectl describe deployment hello
The output is similar to this:
Name: hello Namespace: default CreationTimestamp: Mon, 24 Oct 2016 14:21:02 -0700 Labels: app=hello tier=backend track=stable Selector: app=hello,tier=backend,track=stable Replicas: 7 updated | 7 total | 7 available | 0 unavailable StrategyType: RollingUpdate MinReadySeconds: 0 RollingUpdateStrategy: 1 max unavailable, 1 max surge OldReplicaSets: <none> NewReplicaSet: hello-3621623197 (7/7 replicas created) Events: ...
The key to connecting a frontend to a backend is the backend Service. A Service creates a persistent IP address and DNS name entry so that the backend microservice can always be reached. A Service uses selector labels to find the Pods that it routes traffic to.
First, explore the Service configuration file:
In the configuration file, you can see that the Service routes traffic to Pods
that have the labels
app: hello and
kubectl create -f https://k8s.io/docs/tasks/access-application-cluster/hello-service.yaml
At this point, you have a backend Deployment running, and you have a Service that can route traffic to it.
Now that you have your backend, you can create a frontend that connects to the backend.
The frontend connects to the backend worker Pods by using the DNS name
given to the backend Service. The DNS name is “hello”, which is the value
name field in the preceding Service configuration file.
The Pods in the frontend Deployment run an nginx image that is configured to find the hello backend Service. Here is the nginx configuration file:
Similar to the backend, the frontend has a Deployment and a Service. The
configuration for the Service has
type: LoadBalancer, which means that
the Service uses the default load balancer of your cloud provider.
Create the frontend Deployment and Service:
kubectl create -f https://k8s.io/docs/tasks/access-application-cluster/frontend.yaml
The output verifies that both resources were created:
deployment "frontend" created service "frontend" created
Once you’ve created a Service of type LoadBalancer, you can use this command to find the external IP:
kubectl get service frontend
The external IP field may take some time to populate. If this is the
case, the external IP is listed as
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE frontend 10.51.252.116 <pending> 80/TCP 10s
Repeat the same command again until it shows an external IP address:
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE frontend 10.51.252.116 XXX.XXX.XXX.XXX 80/TCP 1m
The frontend and backends are now connected. You can hit the endpoint by using the curl command on the external IP of your frontend Service.
The output shows the message generated by the backend: