K
Q

Replicaset doesnot update pods in when pod image is modified

1/8/2020

I have created a replicaset with wrong container image with below configuration.

apiVersion: extensions/v1beta1
kind: ReplicaSet
metadata:
  name: rs-d33393
  namespace: default
spec:
  replicas: 4
  selector:
    matchLabels:
      name: busybox-pod
  template:
    metadata:
      labels:
        name: busybox-pod
    spec:
      containers:
      - command:
        - sh
        - -c
        - echo Hello Kubernetes! && sleep 3600
        image: busyboxXXXXXXX
        name: busybox-container

Pods Information:

$ kubectl get pods
NAME              READY     STATUS             RESTARTS   AGE
rs-d33393-5hnfx   0/1       InvalidImageName   0          11m
rs-d33393-5rt5m   0/1       InvalidImageName   0          11m
rs-d33393-ngw78   0/1       InvalidImageName   0          11m
rs-d33393-vnpdh   0/1       InvalidImageName   0          11m

After this, i try to edit the image inside replicaset using kubectl edit replicasets.extensions rs-d33393 and update image as busybox.

Now, i am expecting pods to be recreated with proper image as part of replicaset.

This has not been the exact result.

Can someone please explain, why it is so?

Thanks :)

-- Sravan Kumar
kubernetes
replicaset

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3 Answers

1/8/2020

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.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  creationTimestamp: null
  labels:
    app: busybox
  name: busybox
spec:
  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=true
deployment.apps/busybox created

Check rollout history

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

Update image on deployment

ubuntu@dlv-k8s-cluster-master:~$ kubectl set image deployment.app/busybox *=busybox --record
deployment.apps/busybox image updated


ubuntu@dlv-k8s-cluster-master:~$ kubectl rollout history deployment busybox
deployment.apps/busybox
REVISION  CHANGE-CAUSE
1         kubectl create --filename=busybox.yaml --record=true
2         kubectl set image deployment.app/busybox *=busybox --record=true

Rollback Deployment

ubuntu@dlv-k8s-cluster-master:~$ kubectl rollout undo deployment busybox
deployment.apps/busybox rolled back


ubuntu@dlv-k8s-cluster-master:~$ kubectl rollout history deployment busybox
deployment.apps/busybox
REVISION  CHANGE-CAUSE
2         kubectl set image deployment.app/busybox *=busybox --record=true
3         kubectl create --filename=busybox.yaml --record=true
-- DT.
Source: StackOverflow
1/8/2020

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.

-- Shashank V
Source: StackOverflow
1/8/2020

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.

-- suren
Source: StackOverflow