What is Deployment and Rollingback in kubernetes.

 What is Deployment ?

Deployment provides replication functionality with the help of ReplicaSets, along with various additional capability like rolling out of changes, rollback changes if required.

Deployment flow :-

 

 

3.1 Benefits of Deployment - Rollout Changes

We can easily roll out new updates to our application using deployments.

Deployments will perform an update in a rollout manner to ensure that your app is not down.

 

1. Rollout nginx to nginx:1.17.3

1. Create a first deployment.

# cat deployment/first.yaml

apiVersion: apps/v1

kind: Deployment

metadata:

  name: test-deployment

spec:

  replicas: 3

  selector:

    matchLabels:

      tier: frontend

  template:

    metadata:

      labels:

        tier: frontend

    spec:

      containers:

      - name: nginx-container

        image: nginx:1.17.3

# kubectl apply -f first.yaml

# kubectl describe deployments test-deployment

# kubectl  get deploy

# kubectl get  rs

# kubectl rollout status deploy test-deployment

# kubectl rollout history deploy test-deployment

# kubectl rollout history deploy test-deployment --revision 2

2.Deployment Strategies types :-

1.Recreate :- 

In this type of very simple deployment, all of the old pods are killed all at once and get replaced all at once with the new ones.

2.RollingUpdate ( Ramped or Incremental ) :-

The rolling deployment is the standard default deployment to Kubernetes. It works by slowly, one by one, replacing pods of the previous version of your application with pods of the new version without any cluster downtime.

3.Canary :-

10 instances, first 2 instance deployed new version & test is done then new version deployed on 8 instances. Full deployment has been done, after that old version instance will be deleted.

4.blue / Green :-

In a blue/green deployment strategy (sometimes referred to as red/black) the old version of the application (green) and the new version (blue) get deployed at the same time. When both of these are deployed, users only have access to the green; whereas, the blue is available to your QA team for test automation on a separate service or via direct port-forwarding.

 3 Benefits of Deployment - Rollback Changes

Sometimes, you may want to rollback a Deployment; for example, when the Deployment is not stable, such as crash looping

 

Deployment ensures that only a certain number of Pods are down while they are being updated.

By default, it ensures that at least 25% of the desired number of Pods are up (25% max unavailable)

Deployments keep the history of revisions that had been made.

 

Rolling back to revision=1

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

# kubectl describe deployments test-deployment

Revision=1 will be removed from the rollout history deployment.

# kubectl rollout history deploy test-deployment

Create an object via CLI :-

1. Create a Deployment:

# kubectl create deployment <deployment-name> --image=<image-name>:<tag>

Generating deployment Manifest via CLI Dry run :-

# kubectl create deployment my-deployment --image=nginx  --replicas 3  --dry-run=client -o yaml

 

# kubectl create deployment --help

2.Get Deployments:

# kubectl get deployments

3.Describe a Deployment:

# kubectl describe deployment <deployment-name>

4.Update a Deployment's Image:

# kubectl set image deployment/<deployment-name> <container-name>=<new-image-name>:<tag>

5.Scale a Deployment:

# kubectl scale deployment <deployment-name> --replicas=<number-of-replicas>

6.Rollout Status of a Deployment:

# kubectl rollout status deployment/<deployment-name>

7.Rolling Back a Deployment:

# kubectl rollout undo deployment/<deployment-name>

8.Pause and Resume a Deployment:

# kubectl rollout pause deployment/<deployment-name>

# kubectl rollout resume deployment/<deployment-name>

9.Edit a Deployment:

# kubectl edit deployment <deployment-name>

10.Delete a Deployment:

# kubectl delete deployment <deployment-name>