Replicaset doesnot update pods in when pod image is modified

With ReplicaSets directly you have to kill the old pod, so the new ones will be created with the right image.

If you would be using a Deployment, and you should, changing the image would force the pod to be re-created.

Replicaset does not support updates. As long as required number of pods exist matching the selector labels, replicaset's jobs is done. You should use Deployment instead.

https://kubernetes.io/docs/concepts/workloads/controllers/replicaset/

From the docs:

To update Pods to a new spec in a controlled way, use a Deployment, as ReplicaSets do not support a rolling update directly.

Deployment is a higher-level concept that manages ReplicaSets and provides declarative updates to Pods. Therefore, it is recommend to use Deployments instead of directly using ReplicaSets unless you don’t require updates at all. ( i.e. one may never need to manipulate ReplicaSet objects when using a Deployment)

Its easy to perform rolling updates and rollbacks when deployed using deployments.

$ kubectl create deployment busybox --image=busyboxxxxxxx --dry-run -o yaml > busybox.yaml$ cat busybox.yamlapiVersion: apps/v1kind: Deploymentmetadata:  creationTimestamp: null  labels:    app: busybox  name: busyboxspec:  replicas: 1  selector:    matchLabels:      app: busybox  strategy: {}  template:    metadata:      creationTimestamp: null      labels:        app: busybox    spec:      containers:      - image: busyboxxxxxxx        name: busyboxxxxxxx

ubuntu@dlv-k8s-cluster-master:~$ kubectl create -f busybox.yaml --record=truedeployment.apps/busybox created

Check rollout history

ubuntu@dlv-k8s-cluster-master:~$ kubectl rollout history deployment busyboxdeployment.apps/busyboxREVISION  CHANGE-CAUSE1         kubectl create --filename=busybox.yaml --record=true

Update image on deployment

ubuntu@dlv-k8s-cluster-master:~$ kubectl set image deployment.app/busybox *=busybox --recorddeployment.apps/busybox image updatedubuntu@dlv-k8s-cluster-master:~$ kubectl rollout history deployment busyboxdeployment.apps/busyboxREVISION  CHANGE-CAUSE1         kubectl create --filename=busybox.yaml --record=true2         kubectl set image deployment.app/busybox *=busybox --record=true

Rollback Deployment

ubuntu@dlv-k8s-cluster-master:~$ kubectl rollout undo deployment busyboxdeployment.apps/busybox rolled backubuntu@dlv-k8s-cluster-master:~$ kubectl rollout history deployment busyboxdeployment.apps/busyboxREVISION  CHANGE-CAUSE2         kubectl set image deployment.app/busybox *=busybox --record=true3         kubectl create --filename=busybox.yaml --record=true