ReplicationController

• A ReplicationController ensures that a desired number of pod replicas are running at any one time.
• A ReplicationController makes sure that a pod or a homogeneous set of pods is always up and available

Working style of ReplicationController

• ReplicationController creates if less number of pods are available or terminates extra pods if there are too many pods
• It replaces if any one of pod is deleted or failed.
• ReplicationController supervises multiple pods across multiple nodes
• ReplicationController is often abbreviated to "rc" or "rcs" in discussion, and as a shortcut in kubectl commands.

EX:- If pods are re-created on a node after disruptive maintenance such as a kernel upgrade. for this reason, use ReplicationController if if your application require only single-pod

Creating a ReplicationController

Create rc.yml with following content

Get the file (rc.yml)

apiVersion: v1
kind: ReplicationController
metadata:
  name: nodeapp
spec:
  replicas: 3
  selector:
    app: nodeapp
  template:
    metadata:
      name: nodeapp
      labels:
        app: nodeapp
    spec:
      containers:
      - name: nodeapp
        image: kammana/nodeapp:v1
        ports:
        - containerPort: 8080

Command to create ReplicationController

Syntax: kubectl create -f FILE_NAME

$ kubectl create -f rc.yml

Command to get all ReplicationController

Syntax: kubectl get rc

$ kubectl get rc

Command to describe ReplicationController

Syntax: kubectl describe rc REPLICATIONCONTROLLER_NAME

$ kubectl describe rc nodeapp

Command to Expose ReplicationController to Internet

By default ReplicationController run in a isolated environment i.e. they are reachable within kubernetes cluster, if you wanna reach your ReplicationController outside cluster, You have to expose it

Syntax: kubectl expose rc REPLICATIONCONTROLLER_NAME --type="NodePort" --port CONTAINER_PORT

$ kubectl expose rc nodeapp --type="NodePort" --port 8080