When you initiate a deployment task, a new rollout get initiated. Every new rollout creates a deployment revision.
When you initiate another deployment task, new deployment revision ‘Revision 2’ gets created.
Why revisions?
Revisions are used to keep track of the deployment and made the rollbacks easy.
Recreate Strategy
Delete all the Pods and recreate the Pods again with a specified image. In this strategy, Application downtime exists.
Rolling Update
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.
Let’s see, how can we perform an update and undo operations using Deployment Object.
Step 1: Create a new deployment.
notificationServiceDeployment.yml
apiVersion: apps/v1
kind: Deployment
metadata:
name: notification-service-deployment
labels:
app: notification-service-deployment
author: krishna
serviceType: webservice
spec:
template:
metadata:
name: notification-service
labels:
app: notification-service
author: krishna
serviceType: webservice
spec:
containers:
- name: notification-service-container
image: jboss/wildfly:10.1.0.Final
replicas: 10
selector:
matchLabels:
app: notification-service
Let’s create deployment by executing the below command.
kubectl create -f notificationServiceDeployment.yml
$kubectl create -f notificationServiceDeployment.yml
deployment.apps/notification-service-deployment createdCheck the rollout status
Check the rollout status by executing the below command.
kubectl rollout status deployment/my-deployment
$kubectl rollout status deployment/notification-service-deployment
Waiting for deployment "notification-service-deployment" rollout to finish: 0 of 10 updated replicas are available...
Waiting for deployment "notification-service-deployment" rollout to finish: 1 of 10 updated replicas are available...
Waiting for deployment "notification-service-deployment" rollout to finish: 2 of 10 updated replicas are available...
Waiting for deployment "notification-service-deployment" rollout to finish: 3 of 10 updated replicas are available...
Waiting for deployment "notification-service-deployment" rollout to finish: 4 of 10 updated replicas are available...
Waiting for deployment "notification-service-deployment" rollout to finish: 5 of 10 updated replicas are available...
Waiting for deployment "notification-service-deployment" rollout to finish: 6 of 10 updated replicas are available...
Waiting for deployment "notification-service-deployment" rollout to finish: 7 of 10 updated replicas are available...
Waiting for deployment "notification-service-deployment" rollout to finish: 8 of 10 updated replicas are available...
Waiting for deployment "notification-service-deployment" rollout to finish: 9 of 10 updated replicas are available...
deployment "notification-service-deployment" successfully rolled out
Check rollout history
Execute the below command to see rollout history.
kubectl rollout history deployment/my-deployment
$kubectl rollout history deployment/notification-service-deployment
deployment.apps/notification-service-deployment
REVISION CHANGE-CAUSE
1 <none>
As you see Revision 1 is created for the deployment.
When you initiate a deployment, Kubernetes automatically create a Replicaset for us.
$kubectl get all
NAME READY STATUS RESTARTS AGE
pod/notification-service-deployment-cdf5795d4-7pw86 1/1 Running 0 7m23s
pod/notification-service-deployment-cdf5795d4-98th2 1/1 Running 0 7m23s
pod/notification-service-deployment-cdf5795d4-9g8lg 1/1 Running 0 7m23s
pod/notification-service-deployment-cdf5795d4-jjzvq 1/1 Running 0 7m23s
pod/notification-service-deployment-cdf5795d4-mgdpr 1/1 Running 0 7m23s
pod/notification-service-deployment-cdf5795d4-n8kpj 1/1 Running 0 7m23s
pod/notification-service-deployment-cdf5795d4-pkrg9 1/1 Running 0 7m23s
pod/notification-service-deployment-cdf5795d4-q4zhw 1/1 Running 0 7m23s
pod/notification-service-deployment-cdf5795d4-zqx76 1/1 Running 0 7m23s
pod/notification-service-deployment-cdf5795d4-zrbqs 1/1 Running 0 7m23s
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 28d
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/notification-service-deployment 10/10 10 10 7m23s
NAME DESIRED CURRENT READY AGE
replicaset.apps/notification-service-deployment-cdf5795d4 10 10 10 7m23s
Step 2: Let’s update the jboss/wildfly to some other version jboss/wildfly:15.0.0.Final.
When you initiate updation, Kubernetes create another replica set to deploy pods with new revision.
Let’s confirm this experimentally.
$kubectl get replicaset
NAME DESIRED CURRENT READY AGE
notification-service-deployment-cdf5795d4 10 10 10 8m26s
As you see the output there is one replicaset present now.
$kubectl set image deployment/notification-service-deployment notification-service-container=jboss/wildfly:15.0.0.Final
deployment.apps/notification-service-deployment image updated
Check the rollout status
$kubectl rollout status deployment/notification-service-deployment
Waiting for deployment "notification-service-deployment" rollout to finish: 5 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 5 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 5 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 6 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 6 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 6 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 6 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 6 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 7 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 7 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 7 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 7 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 7 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 7 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 7 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 7 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 8 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 9 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 9 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 9 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 9 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 9 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 2 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 2 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 2 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 2 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 1 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 1 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 8 of 10 updated replicas are available...
Waiting for deployment "notification-service-deployment" rollout to finish: 9 of 10 updated replicas are available...
deployment "notification-service-deployment" successfully rolled out
Check the rollout history.
$kubectl rollout history deployment/notification-service-deployment
deployment.apps/notification-service-deployment
REVISION CHANGE-CAUSE
1 <none>
2 <none>
As you see the output, 2nd revision gets created.
When you query replicasets, you confirm that two replicasets get created. Whenever you initiate a deployment, a new replicaset created to take care of the deployment of the Pods.
$kubectl get replicaset -o wide
NAME DESIRED CURRENT READY AGE CONTAINERS IMAGES SELECTOR
notification-service-deployment-5b9b7ffc68 10 10 10 3m46s notification-service-container jboss/wildfly:15.0.0.Final app=notification-service,pod-template-hash=5b9b7ffc68
notification-service-deployment-cdf5795d4 0 0 0 16m notification-service-container jboss/wildfly:10.1.0.Final app=notification-service,pod-template-hash=cdf5795d4
As you see currently active replica set pointing to the image ‘jboss/wildfly:15.0.0.Final’.
Step 3: You can confirm the rolling update strategy by describing the deployment.
$kubectl describe deployment notification-service-deployment
Name: notification-service-deployment
Namespace: default
CreationTimestamp: Fri, 05 Jun 2020 10:10:46 +0530
Labels: app=notification-service-deployment
author=krishna
serviceType=webservice
Annotations: deployment.kubernetes.io/revision: 2
Selector: app=notification-service
Replicas: 10 desired | 10 updated | 10 total | 10 available | 0 unavailable
StrategyType: RollingUpdate
MinReadySeconds: 0
RollingUpdateStrategy: 25% max unavailable, 25% max surge
Pod Template:
Labels: app=notification-service
author=krishna
serviceType=webservice
Containers:
notification-service-container:
Image: jboss/wildfly:15.0.0.Final
Port: <none>
Host Port: <none>
Environment: <none>
Mounts: <none>
Volumes: <none>
Conditions:
Type Status Reason
---- ------ ------
Available True MinimumReplicasAvailable
Progressing True NewReplicaSetAvailable
OldReplicaSets: <none>
NewReplicaSet: notification-service-deployment-5b9b7ffc68 (10/10 replicas created)
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 18m deployment-controller Scaled up replica set notification-service-deployment-cdf5795d4 to 10
Normal ScalingReplicaSet 6m41s deployment-controller Scaled up replica set notification-service-deployment-5b9b7ffc68 to 3
Normal ScalingReplicaSet 6m41s deployment-controller Scaled down replica set notification-service-deployment-cdf5795d4 to 8
Normal ScalingReplicaSet 6m41s deployment-controller Scaled up replica set notification-service-deployment-5b9b7ffc68 to 5
Normal ScalingReplicaSet 5m40s deployment-controller Scaled down replica set notification-service-deployment-cdf5795d4 to 7
Normal ScalingReplicaSet 5m40s deployment-controller Scaled up replica set notification-service-deployment-5b9b7ffc68 to 6
Normal ScalingReplicaSet 5m37s deployment-controller Scaled down replica set notification-service-deployment-cdf5795d4 to 6
Normal ScalingReplicaSet 5m37s deployment-controller Scaled up replica set notification-service-deployment-5b9b7ffc68 to 7
Normal ScalingReplicaSet 5m35s deployment-controller Scaled down replica set notification-service-deployment-cdf5795d4 to 5
Normal ScalingReplicaSet 5m35s deployment-controller Scaled up replica set notification-service-deployment-5b9b7ffc68 to 8
Normal ScalingReplicaSet 5m29s (x7 over 5m35s) deployment-controller (combined from similar events): Scaled down replica set notification-service-deployment-cdf5795d4 to 0
As you see the Events: section of the output, old deployment replica set scaled-down, while new deployment replica set scaled up.
Step 4: Rollback to the previous deployment.
Let’s query replicasets first.
$kubectl get replicaset -o wide
NAME DESIRED CURRENT READY AGE CONTAINERS IMAGES SELECTOR
notification-service-deployment-5b9b7ffc68 10 10 10 16m notification-service-container jboss/wildfly:15.0.0.Final app=notification-service,pod-template-hash=5b9b7ffc68
notification-service-deployment-cdf5795d4 0 0 0 28m notification-service-container jboss/wildfly:10.1.0.Final app=notification-service,pod-template-hash=cdf5795d4
As you see replicaset ‘notification-service-deployment-5b9b7ffc68’ which points to the image ‘jboss/wildfly:15.0.0.Final’ is active.
Now when I rollback the deployment to the previous state, the deployment destroys the pods in new replica set and creates pods in old replica set.
You can rollback to the previous deployment by executing below command
kubectl rollout undo deployment/notification-service-deployment
$kubectl rollout undo deployment/notification-service-deployment
deployment.apps/notification-service-deployment rolled back
Query for replica sets again.
$kubectl get replicaset -o wide
NAME DESIRED CURRENT READY AGE CONTAINERS IMAGES SELECTOR
notification-service-deployment-5b9b7ffc68 0 0 0 19m notification-service-container jboss/wildfly:15.0.0.Final app=notification-service,pod-template-hash=5b9b7ffc68
notification-service-deployment-cdf5795d4 10 10 10 32m notification-service-container jboss/wildfly:10.1.0.Final app=notification-service,pod-template-hash=cdf5795d4
You can confirm that the older replica set has 10 Pods, where a new replica set has 0 pods.
Now, you can see revision number 3 gets created.
$kubectl rollout history deployment/notification-service-deployment
deployment.apps/notification-service-deployment
REVISION CHANGE-CAUSE
2 <none>
3 <none>
Step 5: You can even update the deployment definition file and apply the changes using ‘kubectl apply’ command.
For example, I changed the image to 19.1.0.
image: jboss/wildfly:19.1.0.Final
notificationServiceDeployment.yml
apiVersion: apps/v1
kind: Deployment
metadata:
name: notification-service-deployment
labels:
app: notification-service-deployment
author: krishna
serviceType: webservice
spec:
template:
metadata:
name: notification-service
labels:
app: notification-service
author: krishna
serviceType: webservice
spec:
containers:
- name: notification-service-container
image: jboss/wildfly:19.1.0.Final
replicas: 10
selector:
matchLabels:
app: notification-service
Apply the changes using the below command.
$kubectl apply -f notificationServiceDeployment.yml
Warning: kubectl apply should be used on resource created by either kubectl create --save-config or kubectl apply
deployment.apps/notification-service-deployment configuredExecute rollout status command to see the rollout status.
$kubectl apply -f notificationServiceDeployment.yml
Warning: kubectl apply should be used on resource created by either kubectl create --save-config or kubectl apply
deployment.apps/notification-service-deployment configured
$kubectl rollout status deployment/notification-service-deployment
Waiting for deployment "notification-service-deployment" rollout to finish: 5 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 5 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 5 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 5 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 5 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 6 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 6 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 6 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 6 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 6 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 7 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 7 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 7 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 7 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 8 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 8 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 8 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 9 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 9 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 9 out of 10 new replicas have been updated...
Waiting for deployment "notification-service-deployment" rollout to finish: 3 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 3 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 3 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 3 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 2 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 2 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 1 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 1 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 1 old replicas are pending termination...
Waiting for deployment "notification-service-deployment" rollout to finish: 8 of 10 updated replicas are available...
Waiting for deployment "notification-service-deployment" rollout to finish: 9 of 10 updated replicas are available...
deployment "notification-service-deployment" successfully rolled out
Now you can see three replica sets.
$kubectl get replicasets
NAME DESIRED CURRENT READY AGE
notification-service-deployment-5b9b7ffc68 0 0 0 87m
notification-service-deployment-6b49cf4b55 10 10 10 99s
notification-service-deployment-cdf5795d4 0 0 0 100m
Now you can see another revision 4 is created.
$kubectl rollout history deployment/notification-service-deployment
deployment.apps/notification-service-deployment
REVISION CHANGE-CAUSE
2 <none>
3 <none>
4 <none>
As you see CHANGE-CAUSE is set to none.
Let’s use the option --record to record the change cause.
Let’s update the definition file to point to the latest image of wildfly.
notificationServiceDeployment.yml
apiVersion: apps/v1
kind: Deployment
metadata:
name: notification-service-deployment
labels:
app: notification-service-deployment
author: krishna
serviceType: webservice
spec:
template:
metadata:
name: notification-service
labels:
app: notification-service
author: krishna
serviceType: webservice
spec:
containers:
- name: notification-service-container
image: jboss/wildfly
replicas: 10
selector:
matchLabels:
app: notification-service
Let’s apply the changes using --record option.
$kubectl apply -f notificationServiceDeployment.yml --record
deployment.apps/notification-service-deployment configured
Now when you execute rollout history command, you can see the change cause against the revision 5.
$kubectl rollout history deployment/notification-service-deployment
deployment.apps/notification-service-deployment
REVISION CHANGE-CAUSE
2 <none>
3 <none>
4 <none>
5 kubectl apply --filename=notificationServiceDeployment.yml --record=true
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