Services

Kubernetes Services provide a way to expose an application running as a set of Pods. They provide an abstract way for clients to access applications without needing to be aware of the application's Pods.

Service Routing

Clients make requests to a Service, which routes traffic to its Pods in a load-balanced fashion.

Endpoints

Endpoints are the backend entities to which Services route traffic. For a Service that routes traffic to multiple Pods, each Pod will have an endpoint associated with the Service.

Tip: One way to determine which Pod(s) a Service is routing traffic to is to look at that service's Endpoints.

Create a deployment.


vi deployment-svc-example.yml
kubectl create -f deployment-svc-example.yml


apiVersion: apps/v1
kind: Deployment
metadata:
  name: deployment-svc-example
spec:
  replicas: 3
  selector:
    matchLabels:
      app: svc-example
  template:
    metadata:
      labels:
        app: svc-example
    spec:
      containers:
      - name: nginx
        image: nginx:1.19.1
        ports:
        - containerPort: 80

Create a ClusterIP Service to expose the deployment's Pods within the cluster network.


vi svc-clusterip.yml
kubectl create -f svc-clusterip.yml


apiVersion: v1
kind: Service
metadata:
  name: svc-clusterip
spec:
  type: ClusterIP
  selector:
    app: svc-example
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80

Get a list of the Service's endpoints.


kubectl get endpoints svc-clusterip

Create a busybox Pod to test your service.


vi pod-svc-test.yml
kubectl create -f pod-svc-test.yml


apiVersion: v1
kind: Pod
metadata:
  name: pod-svc-test
spec:
  containers:
  - name: busybox
    image: radial/busyboxplus:curl
    command: ['sh', '-c', 'while true; do sleep 10; done']

Run a command within the busybox Pod to make a request to the service.


kubectl exec pod-svc-test -- curl svc-clusterip:80

You should see the Nginx welcome page, which is being served by one of the backend Pods created earlier using a Deployment.

Create a NodePort Service to expose the Pods externally.


vi svc-nodeport.yml
kubectl create -f svc-nodeport.yml


apiVersion: v1
kind: Service
metadata:
  name: svc-nodeport
spec:
  type: NodePort
  selector:
    app: svc-example
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80
    nodePort: 30080

Test the service by making a request from your browser to http://<Control Plane Node Public IP>:30080. You should see the Nginx welcome page.