ReplicaSet

About

A ReplicaSet ensures a specified number of Pods are always running.

• If a Pod dies → ReplicaSet spins up a new one.

• If you scale the replica count → more Pods are created.

Uses labels to know which Pods it manages.

Changes inside the Pod, like image version changes, will only be applied for new created Pods.

You usually don’t create ReplicaSets directly, they managed by ReplicaSet (which gives you extra feature).

Commands

To apply and run a Replicaset configuration:

kubectl apply -f replicaset.yaml

To list all the Replicasets, even the ones created by Deployments:

kubectl get replicasets

To describe a Replicaset:

kubectl describe replicaset <replicaset-name>

To delete a Replicaset:

kubectl delete replicaset <replicaset-name>

Example

replicaset.yaml

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: myapp-rs
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp
  # Pod template
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
        - name: myapp-container
          image: nginx:1.25
          ports:
            - containerPort: 80
          env:
            - name: NODE_ENV
              value: "production"