Kubernetes- Deployment

 A Deployment provides declarative updates for Pods ReplicaSets.

You describe a desired state in a Deployment, and the Deployment Controller changes the actual state to the desired state at a controlled rate. You can define Deployments to create new ReplicaSets, or to remove existing Deployments and adopt all their resources with new Deployments.

The following are typical use cases for Deployments:

• Create a Deployment to rollout a ReplicaSet. The ReplicaSet creates Pods in the background. Check the status of the rollout to see if it succeeds or not.
• Declare the new state of the Pods by updating the PodTemplateSpec of the Deployment. A new ReplicaSet is created and the Deployment manages moving the Pods from the old ReplicaSet to the new one at a controlled rate. Each new ReplicaSet updates the revision of the Deployment.
• Rollback to an earlier Deployment revision if the current state of the Deployment is not stable. Each rollback updates the revision of the Deployment.
• Scale up the Deployment to facilitate more load.
• Pause the Deployment to apply multiple fixes to its PodTemplateSpec and then resume it to start a new rollout.
• Use the status of the Deployment as an indicator that a rollout has stuck.
• Clean up older ReplicaSets that you don't need anymore

Create a deployment

kubectl create deployment --image=nginx nginx

Generate Deployment YAML file (-o yaml). Don't create it(--dry-run)

kubectl create deployment --image=nginx nginx --dry-run -o yaml

Generate Deployment with 4 Replicas

kubectl create deployment nginx --image=nginx --replicas=4

You can also scale a deployment using the kubectl scale command.

kubectl scale deployment nginx --replicas=4

LAB

# 1. Deployment YAML file

# nginx-deploy.yaml

apiVersion: apps/v1

kind: Deployment

metadata:

  name: nginx-deploy

  labels:

    app: nginx-app

spec:

  replicas: 3

  template:

    metadata:

      labels:

        app: nginx-app

    spec:

      containers:

      - name: nginx-container

        image: nginx:1.7.9

        ports:

        - containerPort: 80

  selector:

    matchLabels:

      app: nginx-app

Create and Display Deployment

kubectl create -f nginx-deploy.yaml 

kubectl get deploy -l app=nginx-app

kubectl get rs -l app=nginx-app

kubectl get po -l app=nginx-app

kubectl describe deploy nginx-deploy

*******************************************************************

Testing: Rollback update 

kubectl set image deploy nginx-deploy nginx-container=nginx:1.91 --record

kubectl rollout status deployment/nginx-deploy

kubectl rollout history deployment/nginx-deploy

kubectl rollout undo deployment/nginx-deploy

kubectl rollout status deployment/nginx-deploy

kubectl describe deploy nginx-deploy | grep -i image

*******************************************************************

 Testing: Update Version of "nginx:1.7.9"  to "nginx:1.9.1"

kubectl set image deploy nginx-deploy nginx-container=nginx:1.9.1

kubectl edit deploy nginx-deploy

kubectl rollout status deployment/nginx-deploy

kubectl get deploy

*******************************************************************

Testing: Scale UP

kubectl scale deployment nginx-deploy --replicas=5

kubectl get deploy

kubectl get po -o wide

*******************************************************************

Testing: Scale DOWN

kubectl scale deployment nginx-deploy --replicas=3

kubectl get deploy

kubectl get po -o wide

   

*******************************************************************

Cleanup

kubectl delete -f nginx-deploy.yaml

kubectl get deploy

kubectl get rs

kubectl get po 

DaemonSet