ClusterIP

The ClusterIP service is...

an object
acts as a "middleman" between replica pods and other pods
allows "internal cluster" traffic
this is the "default" service type
ClusterIP

A Situation

several frontend web-server pods
several backend service pods
several memory pods (like redis)
several database-connector pods

Some Problems

How does each pod "know" which pod to communicate to?
Pods can go down and come back up without other pods "knowing" about it.

ClusterIP To the Rescue

the ClusterIP Service acts as an object "between" a set of relica pods and the rest of the K8s world.
Each set of pod "services", replicas, can communicate with this clusterIP service, and the clusterIP service will talk to another set of pod services.

Setting up a ClusterIP Service with yaml

apiVersion: v1
kind: Service
metadata:
  name: back-end-cluster-ip
spec:
  type: ClusterIP
  ports:
    # where the "backend" is exposed
    - targetPort: 80
    # where the "service" is exposed
      port: 80
  # link the service to pods by label
  selector:
    app: myapp
    type: back-end

# Run it
Jakes-4:k8s Jake$ kubectl create -f configs/services/cluster-ip.yml 
service/back-end-cluster-ip created

# see it
Jakes-4:k8s Jake$ kubectl get services
NAME                  TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)        AGE
back-end-cluster-ip   ClusterIP   10.105.32.165   <none>        80/TCP         18s
kubernetes            ClusterIP   10.96.0.1       <none>        443/TCP        6d
node-port-service     NodePort    10.97.106.144   1.2.3.110     80:30004/TCP   45h

The service can be accessed by pods by the clusterIP or the service name.

A Local Proxy Is Available

K8s docs.
kubectl proxy docs.

kubectl proxy --port=8080

That will open the kube-api server to http://localhost:8080/api.
Epic.

# get a list of pods in the default namespace
curl http://localhost:8080/api/v1/namespaces/default/pods

Tags:

Kubernetes

k8s

services

nodeport