Deployment Update

Deployment Update

Deployments are intended to replace ReplicationControllers. They provide the same replication functions (through ReplicaSets) and also the ability to rollout changes and roll them back if necessary.

Let’s create a simple Deployment using the same image we’ve been using.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: deployment-test
spec:
  replicas: 3
  selector:
    matchLabels:
      app: deployment-rs
  template:
    metadata:
      labels:
        app: deployment-rs
        environment: dev
    spec:
      containers:
      - name: container01
        image: r.deso.tech/library/nginx
        ports:
        - containerPort: 80

Now go ahead and create the Deployment:

kubectl create -f deploy.yaml

deployment.apps/deployment-test created

Now let’s go ahead and describe the Deployment:

kubectl describe deploy deployment-test

Name:                   deployment-test
Namespace:              default
CreationTimestamp:      Tue, 16 Jul 2019 12:58:13 +0200
Labels:                 <none>
Annotations:            deployment.kubernetes.io/revision: 1
Selector:               app=test-rs
Replicas:               3 desired | 3 updated | 3 total | 3 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  25% max unavailable, 25% max surge
Pod Template:
  Labels:  app=test-rs
           environment=dev
  Containers:
   container01:
    Image:        r.deso.tech/library/nginx
    Port:         80/TCP
    Host Port:    0/TCP
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Conditions:
  Type           Status  Reason
  ----           ------  ------
  Available      True    MinimumReplicasAvailable
  Progressing    True    NewReplicaSetAvailable
OldReplicaSets:  <none>
NewReplicaSet:   deployment-test-5bdd7644cd (3/3 replicas created)
Events:
  Type    Reason             Age   From                   Message
  ----    ------             ----  ----                   -------
  Normal  ScalingReplicaSet  44s   deployment-controller  Scaled up replica set deployment-test-5bdd7644cd to 3

As you can see, rather than listing the individual pods, Kubernetes shows us the ReplicaSet. Notice that the name of the ReplicaSet is the Deployment name and a hash value.

kubectl get deploy,rs,pod

NAME                              READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/deployment-test   0/3     3            0           80s

NAME                                         DESIRED   CURRENT   READY   AGE
replicaset.apps/deployment-test-75d76f9b64   3         3         0       80s

NAME                                   READY   STATUS             RESTARTS   AGE
pod/deployment-test-75d76f9b64-2msxf   0/1     ImagePullBackOff   0          80s
pod/deployment-test-75d76f9b64-6rnk5   0/1     ImagePullBackOff   0          80s
pod/deployment-test-75d76f9b64-gqh9j   0/1     ImagePullBackOff   0          80s
pod/ds-one-b4nmp                       0/1     CrashLoopBackOff   3          2m1s
pod/ds-one-b6m4g                       1/1     Running            0          9m11s
pod/ds-one-lqqqt                       1/1     Running            0          9m11s

As you can see, the Deployment is backed, in this case, by ReplicaSet deployment-test-5bdd7644cd. If we go ahead and look at the list of actual Pods.

Try to delete the ReplicaSet:

kubectl delete rs deployment-test-75d76f9b64

replicaset.apps "deployment-test-75d76f9b64" deleted

Check the state of Ready POD in ReplicaSet

kubectl get rs

NAME                         DESIRED   CURRENT   READY   AGE
deployment-test-75d76f9b64   3         3         0       47s

List pods

kubectl get pods

NAME                               READY   STATUS    RESTARTS   AGE
deployment-test-5bdd7644cd-fqcx9   1/1     Running   0          97s
deployment-test-5bdd7644cd-gf2n8   1/1     Running   0          97s
deployment-test-5bdd7644cd-tqwwc   1/1     Running   0          97s

Your pod name have been changed, because the desired state of Deployment create a new ReplicaSet. Also ReplicaSet created 3 replicas of POD.

The same behaviour happen if you try to delete pod:

kubectl delete pod deployment-test-5bdd7644cd-fqcx9

pod "deployment-test-5bdd7644cd-fqcx9" deleted

List pods:

kubectl get pod

NAME                               READY   STATUS    RESTARTS   AGE
deployment-test-5bdd7644cd-bj2qr   1/1     Running   0          15s
deployment-test-5bdd7644cd-gf2n8   1/1     Running   0          4m20s
deployment-test-5bdd7644cd-tqwwc   1/1     Running   0          4m20s

Scaling Resources

kubectl scale --replicas=5 deployment deployment-test

The new pod have been created in automatically by ReplicaSet according to Deployment desiderated state.

kubectl set image deployment deployment-test container01=r.deso.tech/library/httpd

kubectl rollout status deployment deployment-test

Check your updates:

kubectl rollout history deployment deployment-test

Return to revision 1:

kubectl rollout undo deployment deployment-test --to-revision=1

Let’s clean up before we move on.

kubectl delete deploy deployment-test

deployment.extensions "deployment-test" deleted