Rolling update is the default Deployment strategy in Kubernetes. In this strategy, instead of deleting all the Pods in one shot, we take down one pod at a time. Once a Pod is deleted, a newer Pod with the Specified image gets created. It is the default deployment strategy in Kubernetes.
You can configure a deployment strategy by specifying ‘strategy’ property.
strategy:
type: RollingUpdate
rollingUpdate:
maxSurge: 2
maxUnavailable: 1
maxUnavailble: It specifies the maximum number of Pods that can be upgraded at the same time.
maxSurge: It specifies the maximum number of Pods that can go beyond the desired number of Pods specified in the replica to achieve minimal availability
Step 1: Create a deployment definition file.
rollingUpdate.yml
apiVersion: apps/v1
kind: Deployment
metadata:
name: domain-service-deployment
labels:
app: domain-service-deployment
author: krishna
serviceType: webservice
spec:
template:
metadata:
name: domain-service
labels:
app: domain-service
author: krishna
serviceType: webservice
spec:
containers:
- name: domain-service-container
image: jboss/wildfly
replicas: 5
strategy:
type: RollingUpdate
rollingUpdate:
maxSurge: 2
maxUnavailable: 1
selector:
matchLabels:
app: domain-service
Step 2: Create a deployment using the above definition file.
$kubectl create -f rollingUpdate.yml
deployment.apps/domain-service-deployment created
Query all the deployments.
$kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
domain-service-deployment 5/5 5 5 51s
Step 3: Check the Rollout History of the deployment.
$kubectl Rollout History Deployment domain-service-deployment
deployment.apps/domain-service-deployment
REVISION CHANGE-CAUSE
1
As you see the output, revision 1 is created.
Step 4: let's update the deployment by changing the replicas to 3.
Execute the below command to edit the deployment.
kubectl edit deployment domain-service-deployment
Update the replicas to 3 (For your information, vi editor commands will work here).
$kubectl edit deployment domain-service-deployment
deployment.apps/domain-service-deployment edited
$kubectl rollout history deployment domain-service-deployment
deployment.apps/domain-service-deployment
REVISION CHANGE-CAUSE
1
As you see no new revision is created. Replicas update do not create any new revision.
But, when you update the image, it will create new revision.
Let’s update the image of jboss/wildfly to below one.
jboss/wildfly:19.1.0.Final
$kubectl edit deployment domain-service-deployment
deployment.apps/domain-service-deployment edited
Now after applying the new image version, you can observe that new Revision entry gets created.
$kubectl rollout history deployment domain-service-deployment
deployment.apps/domain-service-deployment
REVISION CHANGE-CAUSE
1
2
You can get what is happened in a revision by executing below command.
kubectl rollout history deployment domain-service-deployment --revision=2
$kubectl rollout history deployment domain-service-deployment --revision=2
deployment.apps/domain-service-deployment with revision #2
Pod Template:
Labels: app=domain-service
author=krishna
pod-template-hash=59b87b89d
serviceType=webservice
Containers:
domain-service-container:
Image: jboss/wildfly:19.1.0.Final
Port:
Host Port:
Environment:
Mounts:
Volumes:
$kubectl get replicaset
NAME DESIRED CURRENT READY AGE
domain-service-deployment-59b87b89d 3 3 3 4m3s
domain-service-deployment-6d8455f97c 0 0 0 13m
$kubectl get replicaset -o wide
NAME DESIRED CURRENT READY AGE CONTAINERS IMAGES SELECTOR
domain-service-deployment-59b87b89d 3 3 3 4m54s domain-service-container jboss/wildfly:19.1.0.Final app=domain-service,pod-template-hash=59b87b89d
domain-service-deployment-6d8455f97c 0 0 0 14m domain-service-container jboss/wildfly app=domain-service,pod-template-hash=6d8455f97c
You can go to previous history by executing undo command.
$kubectl rollout undo deployment domain-service-deployment
deployment.apps/domain-service-deployment rolled back
You can confirm the undo by querying replicaset.
$kubectl get replicaset -o wide
NAME DESIRED CURRENT READY AGE CONTAINERS IMAGES SELECTOR
domain-service-deployment-59b87b89d 0 0 0 6m31s domain-service-container jboss/wildfly:19.1.0.Final app=domain-service,pod-template-hash=59b87b89d
domain-service-deployment-6d8455f97c 3 3 2 16m domain-service-container jboss/wildfly app=domain-service,pod-template-hash=6d8455f97c
You can even go to specific revision by specifying --to-revision option.
$kubectl rollout undo deployment domain-service-deployment --to-revision=2
deployment.apps/domain-service-deployment rolled back
$kubectl get replicaset -o wide
NAME DESIRED CURRENT READY AGE CONTAINERS IMAGES SELECTOR
domain-service-deployment-59b87b89d 3 3 3 7m57s domain-service-container jboss/wildfly:19.1.0.Final app=domain-service,pod-template-hash=59b87b89d
domain-service-deployment-6d8455f97c 0 0 0 17m domain-service-container jboss/wildfly app=domain-service,pod-template-hash=6d8455f97c
These undos and upgrades will create new revisions.
$kubectl rollout history deployment domain-service-deployment
deployment.apps/domain-service-deployment
REVISION CHANGE-CAUSE
3
4 This post first appeared on Java Tutorial : Blog To Learn Java Programming, please read the originial post: here
