Kubernetes - ReplicaSet

 A ReplicaSet's purpose is to maintain a stable set of replica Pods running at any given time. As such, it is often used to guarantee the availability of a specified number of identical Pods.

Replication Controller(Equality based)	ReplicaSet (Set Based
It uses the operators ( =, ==, !=)	Operators ( in, notin,exists)
Example env=prod, env!=stag	Env in(prod)
Command Line kubectl get pods -l env=prod	Kubectl get pods ‘env in(prod,qa)’
Manifest selector:     app: nginx-app	selector:     matchLabels:       app: nginx-app     matchExpressions:       - {key: tier, operator: In, values: [frontend]}

LAB

# nginx-rs.yaml

apiVersion: apps/v1

kind: ReplicaSet

metadata:

  name: nginx-rs

spec:

  replicas: 3

  template:

    metadata:

      name: nginx-pod

      labels:

        app: nginx-app

        tier: frontend

    spec:

      containers:

      - name: nginx-container

        image: nginx

        ports:

        - containerPort: 80

  selector:

    matchLabels:

      app: nginx-app

    matchExpressions:

      - {key: tier, operator: In, values: [frontend]}

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# 2. Create and display replicaset

kubectl create -f nginx-rs.yaml

kubectl get po -o wide

kubectl get po -l app=nginx-app

kubectl get rs nginx-rs -o wide

kubectl describe rs nginx-rs

kubectl get po -l 'tier in (frontend)'

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# 3. Automatic Pod Reschedule 

kubectl get po -o wide --watch

kubectl get po -o wide

kubectl get nodes

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# 4. Scale up pods

kubectl scale rs nginx-rs --replicas=5

kubectl get rs nginx-rs -o wide

kubectl get po -o wide

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# 5. Scale down pods

kubectl scale rs nginx-rs --replicas=3

kubectl get rs nginx-rs -o wide

kubectl get po -o wide

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# 6. Cleanup

kubectl delete -f nginx-rs.yaml

kubectl get rs

kubectl get po -l app=nginx-app

Deployment