ReplicaSet

A Replicaset ensures that a specified number of pod replicas are running at any given time. If a pod fails or is deleted, the Replicaset will create a new pod to replace it.

Example Replicaset Definition

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: myapp-replicaset
  labels:
    app: myapp
    type: front-end
spec:
  template:
    metadata:
      name: myapp-pod
      labels:
        app: myapp
        type: front-end
    spec:
      containers:
      - name: nginx-container
        image: nginx
  
  replicas: 3
  selector:
    matchLabels:
      type: front-end

In this example, we define a Replicaset named myapp-replicaset that maintains 3 replicas of a pod with the label app: myapp. The pod template specifies the container to run, including environment variables sourced from a ConfigMap.

Commands

Create a Replicaset from a definition file:

kubectl create -f myapp-replicaset.yaml

Show the list of Replicasets:

kubectl get rs

Detailed information about a Replicaset:

kubectl describe rs myapp-replicaset

Delete a Replicaset:

kubectl delete rs myapp-replicaset

This command will delete the Replicaset and all its associated pods. Extract the definition to a file:

kubectl get rs myapp-replicaset -o yaml > myapp-replicaset.yaml

This command will output the current definition of the Replicaset to a YAML file named myapp-replicaset.yaml.

kubectl replace -f myapp-replicaset.yaml

This command will replace the existing Replicaset with the definition provided in the myapp-replicaset.yaml file. This is useful for updating the Replicaset configuration without deleting it first

kubectl scale --replicas=6 -f myapp-replicaset.yaml

This command will scale the Replicaset to 6 replicas, creating or deleting pods as necessary to reach the desired count.

kubectl scale --replicas=6 rs myapp-replicaset

This command will also scale the Replicaset named myapp-replicaset to 6 replicas, similar to the previous command but using the rs resource type directly.

kubectl edit rs myapp-replicaset  

This command will open the Replicaset definition in an editor, allowing you to modify its properties. After saving and closing the editor, Kubernetes will apply the changes to the Replicaset.