Services

It is providing a stable network endpoint to one or many pods.

When a pod restart the IP changes, so we cannot rely on those. There is a k8s primitive that provides discoverable names and load balancing to a set of Pods. It's called Service

Exposing a Network Endpoint to Pods

Request routing, the service uses label selection to see which pods can it use.

We also need to do port mapping. contianerPort is the port in the container, targetPort is the port in the service. They need to be the same.

Imperative approach.

k create service clusterip echoserver --tcp=80:8080

Or we can create a pod and a service from one shot.

k run echoserver --image=some-image --port=8080 --expose

This is the manifest approach.

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  selector:
    app.kubernetes.io/name: MyApp
  ports:
    - protocol: TCP
      port: 80
      targetPort: 9376

Service Types (How can we export the service)

• ClusterIP: exposes the service on a cluster-interal ip. Meaning it will only be reachable from pods within the cluster (this is the default).
• NodePort: Exposes the service on each node's IP at a static port.
• LoadBalancer: Exposes the service externally using a cloud provider's load balancer.