Docker & Kubernetes: Rolling Updates

bogotobogo.com site search:

Initial deploy

$ minikube start --nodes 5

$ kubectl get nodes
NAME           STATUS   ROLES    AGE     VERSION
minikube       Ready    master   9m24s   v1.19.0
minikube-m02   Ready    <none>   7m24s   v1.19.0
minikube-m03   Ready    <none>   5m36s   v1.19.0
minikube-m04   Ready    <none>   4m27s   v1.19.0
minikube-m05   Ready    <none>   3m17s   v1.19.0

$ kubectl version
Client Version: version.Info{Major:"1", Minor:"18", GitVersion:"v1.18.0", GitCommit:"9e991415386e4cf155a24b1da15becaa390438d8", GitTreeState:"clean", BuildDate:"2020-03-25T14:58:59Z", GoVersion:"go1.13.8", Compiler:"gc", Platform:"darwin/amd64"}
Server Version: version.Info{Major:"1", Minor:"19", GitVersion:"v1.19.0", GitCommit:"e19964183377d0ec2052d1f1fa930c4d7575bd50", GitTreeState:"clean", BuildDate:"2020-08-26T14:23:04Z", GoVersion:"go1.15", Compiler:"gc", Platform:"linux/amd64"}

nginx-deployment.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx-container
        image: nginx:1.14.2
        ports:
        - containerPort: 80

$ kubectl apply -f nginx-deployment.yaml
deployment.apps/nginx-deployment created    

$ kubectl get pods
NAME                               READY   STATUS    RESTARTS   AGE
nginx-deployment-69b6b46f5-2lw4l   1/1     Running   0          40s
nginx-deployment-69b6b46f5-b9c89   1/1     Running   0          40s
nginx-deployment-69b6b46f5-rkqmp   1/1     Running   0          40s
nginx-deployment-69b6b46f5-snvz4   1/1     Running   0          40s
nginx-deployment-69b6b46f5-wmd6d   1/1     Running   0          40s

Update deployment

$ kubectl get deployment
NAME               READY   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment   5/5     5            5           103m

$ kubectl describe deployment nginx-deployment
Name:                   nginx-deployment
Namespace:              default
CreationTimestamp:      Thu, 22 Apr 2021 10:44:06 -0700
Labels:                 <none>
Annotations:            deployment.kubernetes.io/revision: 1
Selector:               app=nginx
Replicas:               5 desired | 5 updated | 5 total | 5 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  25% max unavailable, 25% max surge
...

A Deployment's rollout is triggered if and only if the Deployment's Pod template (that is, .spec.template) is changed, for example if the labels or container images of the template are updated. Other updates, such as scaling the Deployment, do not trigger a rollout.

Let's update the nginx Pods to use the nginx:1.16.1 image instead of the nginx:1.14.2 image:

$ kubectl set image \
deployment/nginx-deployment nginx-container=nginx:1.16.1 --record
deployment.apps/nginx-deployment image updated

Note that we specified the --record flag to write the command executed in the resource annotation kubernetes.io/change-cause. The recorded change is useful for future introspection:

$ kubectl describe deployment nginx-deployment
Name:                   nginx-deployment
Namespace:              default
CreationTimestamp:      Thu, 22 Apr 2021 10:44:06 -0700
Labels:                 
Annotations:            deployment.kubernetes.io/revision: 2
                        kubernetes.io/change-cause: kubectl set image deployment/nginx-deployment nginx-container=nginx:1.16.1 --record=true
Selector:               app=nginx
Replicas:               5 desired | 5 updated | 5 total | 5 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  25% max unavailable, 25% max surge
Pod Template:
  Labels:  app=nginx
  Containers:
   nginx-container:
    Image:        nginx:1.16.1
...

To see the rollout status:

$ kubectl rollout status deployment/nginx-deployment
deployment "nginx-deployment" successfully rolled out

To check the rollout history:

$ kubectl rollout history deployment.v1.apps/nginx-deployment
REVISION  CHANGE-CAUSE
1         <none>
2         kubectl set image deployment/nginx-deployment nginx-container=nginx:1.16.1 --record=true

Rolling Back to a Previous Revision

Let's rollback the deployment from the current version to the previous version, which is version 1. Undo the current rollout and rollback to the previous revision:

$ kubectl rollout undo deployment.v1.apps/nginx-deployment
deployment.apps/nginx-deployment rolled back

Get the description of the Deployment:

$ kubectl describe deployment nginx-deployment
Name:                   nginx-deployment
Namespace:              default
CreationTimestamp:      Thu, 22 Apr 2021 10:44:06 -0700
Labels:                 <none>
Annotations:            deployment.kubernetes.io/revision: 3
Selector:               app=nginx
Replicas:               5 desired | 5 updated | 5 total | 5 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  25% max unavailable, 25% max surge
Pod Template:
  Labels:  app=nginx
  Containers:
   nginx-container:
    Image:        nginx:1.14.2
...