Replica Set

Overview

Replica set is a next generation replication Controller
Only supports equality based selector whereas the replica set supports set based selector that is filtering according to set of values.
Replica set is used by other objects like deployment rather than the replication controller.
There is no major changes in the manifest file except the kind and the apiVersion

key	Replication Controller	Replica Set
`kind`	`ReplicationController`	`ReplicaSet`
`apiVersion`	`v1`	`apps/v1`

Example of Replica Set

k8s_example_8.yml

kind: ReplicaSet
apiVersion: apps/v1
metadata:
  name: example-8
spec:
  replicas: 2
  selector:
    matchExpressions:
      - key: myname
        operator: In
        values: [xander, billa, kubernetes]
      - key: env
        operator: NotIn
        values: [prod, dev]
  template:
    metadata:
      name: container0
      labels:
        myname: xander
    spec:
      containers:
        - name: c00
          image: ubuntu
          command: ["/bin/bash", "-c", "while true; do echo Hello-World; sleep 5 ; done"]

Create a replicaset

kubectl apply -f k8s_example_8.yml

Output

controlplane $ kubectl apply -f k8s_example_8.yml 
replicaset.apps/example-8 created

Verify the rs and pods

kubectl get rs
kubectl get pods

Output

controlplane $ kubectl get rs
NAME        DESIRED   CURRENT   READY   AGE
example-8   5         5         5       72s

For more details

kubectl describe rs example-8

Output

controlplane $ kubectl describe rs example-8
.
.
.
Replicas:     5 current / 5 desired
Pods Status:  5 Running / 0 Waiting / 0 Succeeded / 0 Failed
.
.
.
Events:
  Type    Reason            Age   From                    Message
  ----    ------            ----  ----                    -------
  Normal  SuccessfulCreate  3m32s  replicaset-controller  Created pod: example-8-wjtkc
  Normal  SuccessfulCreate  3m32s  replicaset-controller  Created pod: example-8-w8qnb

Verify the pods

kubectl get pods

Output

controlplane $ kubectl get pods
NAME              READY   STATUS    RESTARTS   AGE
example-8-w8qnb   1/1     Running   0          4m11s
example-8-wjtkc   1/1     Running   0          4m12s

Note the labels

kubectl get pods --show-labels

Output

controlplane $ kubectl get pods --show-labels
NAME              READY   STATUS    RESTARTS   AGE     LABELS
example-8-w8qnb   1/1     Running   0          4m31s   myname=xander
example-8-wjtkc   1/1     Running   0          4m32s   myname=xander

Tweak the number of desired replica

kubectl scale rs --replicas=2 example-8

Output

controlplane $ kubectl scale rs --replicas=2 example-8   
replicaset.apps/example-8 scaled
controlplane $ kubectl get pods
NAME              READY   STATUS    RESTARTS   AGE
example-8-w8qnb   1/1     Running   0          12m
example-8-wjtkc   1/1     Running   0          12m

Verify the rs

kubectl get rs

Output

controlplane $ kubectl get rs
NAME        DESIRED   CURRENT   READY   AGE
example-8   2         2         2       13m

To delete replica set

kubectl delete rs example-8

Output

controlplane $ kubectl delete rs example-8
replicaset.apps "example-8" deleted

Scaling and Replication Deployment Object