You might want to perform rolling updates to deploy newer versions of an application, i.e. not update them all at once but rather one after the other. This ensures users have access to the application during the upgrade. If one of the updates unexpectedly fails, you want to be able to roll back. If you want to be able to make multiple changes to your environment such as upgrading versions, scaling, or modifying resource allocations, you don’t want to do it all at once.

Deployments

To create a Deployment, it is similar to creating a Replica Set with a YAML file, except that now the kind is Deployment.

deployment-definition.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-deployment
  labels:
    app: myapp
    type: front-end
spec: # Start of the pod template
  template: 
    metadata:
      name: myapp
      labels:
        name: myapp
        type: front-end
    spec:
      containers:
        - name: myapp-container
          image: myapp:v1
replicas: 3
selector:
  matchLabels:
    type: front-end

Create the deployment using the template file:

$ kubectl create -f deployment-definition.yaml

Get deployments to show the new deployment:

$ kubectl get deployments

Also getting the replica sets will show the replicas created in the deployment:

$ kubectl get replicasets

Likewise, running a get on the pods will return all the pods created by the replica set, which was defined by the deployment template file:

$ kubectl get pods

To see all aspects created at once:

$ kubectl get all