Endpoints

What is Endpoints in K8S

When we create a service in K8S, a Endpoint object is also created with the same name as the service. Service knows how to send traffic to corresponding Pods. This is done by a mapping within the Endpoint object.

Lets take a look at some examples

• A wordpress service

  kubectl get svc -n wordpress-ns
  NAME              TYPE           CLUSTER-IP       EXTERNAL-IP                    PORT(S)        AGE
  wordpress         LoadBalancer   10.100.200.174   100.64.144.7,192.168.160.115   80:31895/TCP   3d23h

• wordpress pods

  kubectl get pods -n wordpress-ns -o wide
  NAME                               READY   STATUS    RESTARTS   AGE     IP         NODE                                   NOMINATED NODE   READINESS GATES
  wordpress-dccb8668f-5dfjc          1/1     Running   0          24m     40.0.4.3   244dee94-bfa7-4413-9135-34f902040d7e   <none>           <none>
  wordpress-dccb8668f-ntbm8          1/1     Running   0          3d23h   40.0.4.4   9aeea30f-f08b-47b3-b7aa-ef45f3e800b0   <none>           <none>

• wordpress endpoints

  kubectl get endpoints -n wordpress-ns
  NAME              ENDPOINTS                 AGE
  wordpress         40.0.4.3:80,40.0.4.4:80   3d23h

  kubectl get endpoints wordpress -n wordpress-ns -o yaml
  apiVersion: v1
  kind: Endpoints
  metadata:
    creationTimestamp: "2020-03-11T23:07:17Z"
    labels:
      app: wordpress
    name: wordpress
    namespace: wordpress-ns
    resourceVersion: "30785441"
    selfLink: /api/v1/namespaces/wordpress-ns/endpoints/wordpress
    uid: 0daa2245-63ed-11ea-bd75-005056a6497c
  subsets:
  - addresses:
    - ip: 40.0.4.3
      nodeName: 244dee94-bfa7-4413-9135-34f902040d7e
      targetRef:
        kind: Pod
        name: wordpress-dccb8668f-5dfjc
        namespace: wordpress-ns
        resourceVersion: "30785439"
        uid: edf43dd1-6708-11ea-bd75-005056a6497c
    - ip: 40.0.4.4
      nodeName: 9aeea30f-f08b-47b3-b7aa-ef45f3e800b0
      targetRef:
        kind: Pod
        name: wordpress-dccb8668f-ntbm8
        namespace: wordpress-ns
        resourceVersion: "30463686"
        uid: 0db65784-63ed-11ea-bd75-005056a6497c
    ports:
    - port: 80
      protocol: TCP

As we can see, the Endpoints object as the mapping with corresponding Pod IPs which let the service could know where to send the traffics to.

We could also edit the Endpoints object to let the service sends traffics to some external services outside of the cluster. See this post for more details.