Kubernetes Recreate Strategy

Kubernetes Recreate Strategy

Recreate

There is another deployment strategy called Recreate. Let us edit the deployment again to use another version, v3, this time and change the strategy from RollingUpdate to Recreate.

pradeep@learnk8s$ kubectl edit deployment kodekloud
deployment.apps/kodekloud edited

# Please edit the object below. Lines beginning with a '#' will be ignored,
# and an empty file will abort the edit. If an error occurs while saving this file will be
# reopened with the relevant failures.
#
apiVersion: apps/v1
kind: Deployment
metadata:
  annotations:
    deployment.kubernetes.io/revision: "2"
  creationTimestamp: "2022-02-15T07:13:38Z"
  generation: 2
  labels:
    app: kodekloud
  name: kodekloud
  namespace: default
  resourceVersion: "2408"
  uid: e5728c54-8768-4d5c-b1b0-c3e33cf62062
spec:
  progressDeadlineSeconds: 600
  replicas: 4
  revisionHistoryLimit: 10
  selector:
    matchLabels:
      app: kodekloud
  strategy:
    type: Recreate
  template:
    metadata:
      creationTimestamp: null
      labels:
        app: kodekloud
    spec:
      containers:
      - image: kodekloud/webapp-color:v3
        imagePullPolicy: Always
        name: webapp-color
        resources: {}
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File
      dnsPolicy: ClusterFirst
      restartPolicy: Always
      schedulerName: default-scheduler
      securityContext: {}
      terminationGracePeriodSeconds: 30
status:
-- INSERT --

pradeep@learnk8s$ kubectl get deployments.apps
NAME        READY   UP-TO-DATE   AVAILABLE   AGE
kodekloud   4/4     4            4           33m

pradeep@learnk8s$ kubectl get pods -o wide
NAME                         READY   STATUS    RESTARTS   AGE   IP            NODE      NOMINATED NODE   READINESS GATES
kodekloud-676c6b9fcd-6bm6z   1/1     Running   0          53s   10.244.1.12   k8s-m02   <none>           <none>
kodekloud-676c6b9fcd-dggk7   1/1     Running   0          53s   10.244.0.10   k8s       <none>           <none>
kodekloud-676c6b9fcd-m2q7x   1/1     Running   0          53s   10.244.0.11   k8s       <none>           <none>
kodekloud-676c6b9fcd-p8tnl   1/1     Running   0          53s   10.244.1.11   k8s-m02   <none>           <none>

If we look at the latest events of the deployment, the deployment-controller Scaled down replica set kodekloud-8477b7849 to 0 at a time and Scaled up new replica set kodekloud-676c6b9fcd to 4.

pradeep@learnk8s$ kubectl describe deployments.apps
Name:               kodekloud
Namespace:          default
CreationTimestamp:  Tue, 15 Feb 2022 12:43:38 +0530
Labels:             app=kodekloud
Annotations:        deployment.kubernetes.io/revision: 3
Selector:           app=kodekloud
Replicas:           4 desired | 4 updated | 4 total | 4 available | 0 unavailable
StrategyType:       Recreate
MinReadySeconds:    0
Pod Template:
  Labels:  app=kodekloud
  Containers:
   webapp-color:
    Image:        kodekloud/webapp-color:v3
    Port:         <none>
    Host Port:    <none>
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Conditions:
  Type           Status  Reason
  ----           ------  ------
  Available      True    MinimumReplicasAvailable
  Progressing    True    NewReplicaSetAvailable
OldReplicaSets:  <none>
NewReplicaSet:   kodekloud-676c6b9fcd (4/4 replicas created)
Events:
  Type    Reason             Age    From                   Message
  ----    ------             ----   ----                   -------
  Normal  ScalingReplicaSet  35m    deployment-controller  Scaled up replica set kodekloud-589c9f4b47 to 4
  Normal  ScalingReplicaSet  20m    deployment-controller  Scaled up replica set kodekloud-8477b7849 to 1
  Normal  ScalingReplicaSet  20m    deployment-controller  Scaled down replica set kodekloud-589c9f4b47 to 3
  Normal  ScalingReplicaSet  20m    deployment-controller  Scaled up replica set kodekloud-8477b7849 to 2
  Normal  ScalingReplicaSet  20m    deployment-controller  Scaled down replica set kodekloud-589c9f4b47 to 2
  Normal  ScalingReplicaSet  20m    deployment-controller  Scaled up replica set kodekloud-8477b7849 to 3
  Normal  ScalingReplicaSet  20m    deployment-controller  Scaled down replica set kodekloud-589c9f4b47 to 1
  Normal  ScalingReplicaSet  20m    deployment-controller  Scaled up replica set kodekloud-8477b7849 to 4
  Normal  ScalingReplicaSet  19m    deployment-controller  Scaled down replica set kodekloud-589c9f4b47 to 0
  Normal  ScalingReplicaSet  2m58s  deployment-controller  Scaled down replica set kodekloud-8477b7849 to 0
  Normal  ScalingReplicaSet  2m27s  deployment-controller  Scaled up replica set kodekloud-676c6b9fcd to 4

Just to verify, let us connect to one of the pods from the new version and check the output.

pradeep@learnk8s$ minikube ssh -p k8s
                         _             _
            _         _ ( )           ( )
  ___ ___  (_)  ___  (_)| |/')  _   _ | |_      __
/' _ ` _ `\| |/' _ `\| || , <  ( ) ( )| '_`\  /'__`\
| ( ) ( ) || || ( ) || || |\`\ | (_) || |_) )(  ___/
(_) (_) (_)(_)(_) (_)(_)(_) (_)`\___/'(_,__/'`\____)

$ curl 10.244.1.12:8080
<!doctype html>
<title>Hello from Flask</title>
<body style="background: #e74c3c;"></body>
<div style="color: #e4e4e4;
    text-align:  center;
    height: 90px;
    vertical-align:  middle;">

  <h1>Hello from kodekloud-676c6b9fcd-6bm6z!</h1>



  <h2>
    Application Version: v3
  </h2>


</div>$

From this, it is clear that the application got upgraded to latest version.

Also, there is another test to verify the color used by the web-app. All four pods returned red.

$ curl 10.244.1.12:8080/color
red$ curl 10.244.1.11:8080/color
red$ curl 10.244.0.11:8080/color
red$ curl 10.244.0.10:8080/color
red$