• Provides the capability to upgrade the instances seamlessly using rolling updates, rollback to previous versions seamlessly, undo, pause and resume changes as required.
• Abstraction over ReplicaSet.
• Blueprint for stateless pods (application layer).
• When a deployment is created, it automatically creates a ReplicaSet which in turn creates pods. If we run k get all we can see the resources created by deployment.

Config YAML file

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apiVersion: apps/v1
kind: Deployment
metadata:
  name: httpd-frontend
  labels:
    name: frontend
spec:
  replicas: 3
  selector:
    matchLabels:
      name: frontend
  template:
    metadata:
      labels:
        name: frontend
    spec:
      containers:
      - name: httpd
        image: httpd:2.4-alpine

Deployment Strategy

There are two deployment strategies:

• Recreate: Bring down all the running containers and then bring up the newer version (application downtime)
• Rolling Update (default): Bring down a container and then bring up a new container one at a time (no application downtime)

Rollout and Versioning

• When you first create a deployment, it triggers a rollout which creates the first revision of the deployment. Every subsequent update to the deployment triggers a rollout which creates a new revision of the deployment. This keeps a track of the deployment and helps us rollback to a previous version of the deployment if required.

• When we upgrade the version of a deployment, a new replica set is created under the hood where the new pods are spawned while bringing down pods from the old replica set one at a time, following a rolling update strategy. We can see the new and old replica sets by running k get replicasets

  

• k rollout status deployment <deployment-name> - view the status of rollout for a deployment

• k rollout history deployment <deployment-name> - view the history of rollouts for a deployment

• k rollout history deployment <deployment-name> --revision=1 - view the status of rollouts for a deployment revision

Rollback

• When we rollback to the previous version of a deployment, the pods in the current replica set are brought down one at a time while spawning pods in the previous replica set.

• Rollback a deployment - k rollout undo deployment <deployment-name>

• Rollback a deployment to a specific revision - k rollout undo deployment <deployment-name> --to-revision=1