ReplicaSet Controller

Create manifest file for Replica Set

Create "CreateReplicaSet.yaml" file with below manifest definitions

#Replica Set with Set-Based Selectors
apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: nginx-rs

spec:
  replicas: 5
  selector:
    matchLabels:
      app: nginx-app
    matchExpressions:
      - {key: tier, operator: IN, values: [frontend]}
    
  template:
    name: nginx-pod
    labels:
      app: nginx-app
      tier: frontend
  spec:
    containers:
    - name: nginx-container
      image: nginx
      ports:
      - containerPort: 80

Deploy Replica Set

[root@ ~]$kubectl apply -f CreateReplicaSet.yaml
replicaset.apps/nginx-rs created
[root@ ~]$

Verify running PODs in the cluster

[root@ ~]$kubectl get pods
NAME             READY   STATUS    RESTARTS   AGE
nginx-rs-6p274   1/1     Running   0          33s
nginx-rs-pfbfd   1/1     Running   0          33s
nginx-rs-w6xv6   1/1     Running   0          33s
[root@ ~]$kubectl get po
NAME             READY   STATUS    RESTARTS   AGE
nginx-rs-6p274   1/1     Running   0          39s
nginx-rs-pfbfd   1/1     Running   0          39s
nginx-rs-w6xv6   1/1     Running   0          39s
[iwayQ@ ~]$

Verify running Replica Set in the cluster

[root@ ~]$kubectl get rs
NAME       DESIRED   CURRENT   READY   AGE
nginx-rs   3         3         3       60s
[root@ ~]$kubectl get rs -o wide
NAME       DESIRED   CURRENT   READY   AGE   CONTAINERS        IMAGES   SELECTOR
nginx-rs   3         3         3       64s   nginx-container   nginx    app=nginx-app,tier in (frontend)
[root@ ~]$kubectl get rs nginx-rs
NAME       DESIRED   CURRENT   READY   AGE
nginx-rs   3         3         3       73s
[root@ ~]$

Describe running Replica Set properties and events

[root@ ~]$kubectl describe rs nginx-rs
Name:         nginx-rs
Namespace:    default
Selector:     app=nginx-app,tier in (frontend)
Labels:       <none>
Annotations:  Replicas:  3 current / 3 desired
Pods Status:  3 Running / 0 Waiting / 0 Succeeded / 0 Failed
Pod Template:
  Labels:  app=nginx-app
           tier=frontend
  Containers:
   nginx-container:
    Image:        nginx
    Port:         80/TCP
    Host Port:    0/TCP
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Events:
  Type    Reason            Age   From                   Message
  ----    ------            ----  ----                   -------
  Normal  SuccessfulCreate  104s  replicaset-controller  Created pod: nginx-rs-w6xv6
  Normal  SuccessfulCreate  104s  replicaset-controller  Created pod: nginx-rs-pfbfd
  Normal  SuccessfulCreate  104s  replicaset-controller  Created pod: nginx-rs-6p274
[root@ ~]$

Scale Out POD replicas manged by Replica Set

[root@ ~]$kubectl scale rs nginx-rs --replicas=5
replicaset.apps/nginx-rs scaled
[root@ ~]$kubectl get pods
NAME             READY   STATUS    RESTARTS   AGE
nginx-rs-6p274   1/1     Running   0          2m38s
nginx-rs-lqdcg   1/1     Running   0          6s
nginx-rs-pfbfd   1/1     Running   0          2m38s
nginx-rs-vbmqg   1/1     Running   0          6s
nginx-rs-w6xv6   1/1     Running   0          2m38s
[root@ ~]$

Scale In POD replicas managed by Replica Set

[root@ ~]$kubectl scale rs nginx-rs --replicas=3
replicaset.apps/nginx-rs scaled
[root@ ~]$kubectl get pods
NAME             READY   STATUS        RESTARTS   AGE
nginx-rs-6p274   1/1     Running       0          2m59s
nginx-rs-lqdcg   0/1     Terminating   0          27s
nginx-rs-pfbfd   1/1     Running       0          2m59s
nginx-rs-vbmqg   0/1     Terminating   0          27s
nginx-rs-w6xv6   1/1     Running       0          2m59s
[root@ ~]$kubectl get pods
NAME             READY   STATUS    RESTARTS   AGE
nginx-rs-6p274   1/1     Running   0          3m9s
nginx-rs-pfbfd   1/1     Running   0          3m9s
nginx-rs-w6xv6   1/1     Running   0          3m9s
[iwayQ@ ~]$

Delete Replica Set

[root@ ~]$kubectl delete rs nginx-rs
replicaset.apps "nginx-rs" deleted
[root@ ~]$kubectl get rs
No resources found in default namespace.
[root@ ~]$kubectl get pods
No resources found in default namespace.
[root~]$