In Kubernetes, how to set pods' names when using replication controllers?

Question

I have a simple replication controller yaml file which looks like this:

apiVersion: v1
kind: ReplicationController
metadata:
  name: nginx
spec:
  replicas: 3
           


        

Answer 1

This can be implemented using statefulsets which is out of beta since version 1.9. Quoting the documentation: When using kind: StatefulSet,

Pods have a unique identity that is comprised of an ordinal, a stable network identity, and stable storage. The identity sticks to the Pod, regardless of which node it’s (re)scheduled on.

Each Pod in a StatefulSet derives its hostname from the name of the StatefulSet and the ordinal of the Pod. The pattern for the constructed hostname is $(statefulset name)-$(ordinal).

So in the example above, you would get nginx-0,nginx-1,nginx-2

Answer 2

If you're running stateless workloads, I cannot imagine why you would want to have fixed identities associated with each object if your intention is to run N replicas of a particular pod.

There is no way to do this using a ReplicaSet/ReplicationController. When the controller creates new pods, it will have a generated name suffix after the pod name.

If that is what you really want (fixed identity/ordinal index), the property is satisfied by the StatefulSet resource which is stable since Kubernetes v1.9. However, it also comes with additional guarantees that you probably do not need.

Answer 3

You should be using statefulset instead of replication controllers. Moreover, replication controllers are replaced with ReplicaSets.

StatefulSet Pods have a unique identity that is comprised of an ordinal. For a StatefulSet with N replicas, each Pod in the StatefulSet will be assigned an integer ordinal, from 0 up through N-1, that is unique over the Set. Each Pod in a StatefulSet derives its hostname from the name of the StatefulSet and the ordinal of the Pod.

StatefulSets matches your requirements and hence use it in your deployment.

Try the deployment files below:

apiVersion: v1
kind: Service
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: nginx
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  selector:
    matchLabels:
      app: nginx # has to match .spec.template.metadata.labels
  serviceName: "nginx"
  replicas: 3 # by default is 1
  template:
    metadata:
      labels:
        app: nginx # has to match .spec.selector.matchLabels
    spec:
      terminationGracePeriodSeconds: 10
      containers:
      - name: nginx
        image: k8s.gcr.io/nginx-slim:0.8
        ports:
        - containerPort: 80
          name: web
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
      volumes:
      - name: www
        emptyDir: