Kubernetes Deployments in simple terms

Kubernetes Deployments are a higher level Object in Kubernetes. If we were to draw a diagram of the Objects we learnt so far, here is how it looks like.

The Deployment provides us with capability such as updating instances seamlessly using rolling updates, pause, undo & resume changes as required.

How to we create a deployment ?

We create a Yaml file. The contents of the Deployment file are very similar to that of a Replica set except for the kind which is going to be deployment.

apiVersion: v1
kind: deployment
metadata:
  name: my-rc
  labels:
    app: mytestapp
    type: front-end
spec:
  template:
    metadata
        name: nginx
        labels:
             app: nginx
             type: frontend

    spec:
        containers: 
           - name: nginx-container
             image: nginx
replicas: 3
selector:
  matchLabels:
    type: front-end

Once the file is ready, use the kubectl create -f {filename.yml} & use the kubectl get deployments to get the status.

kubectl get all command can be used to view all types of objects.

Update & Rollbacks:

When we first deploy our application, it creates a rollout. A new rollout creates revisioning named revision 1, in future, when the application is upgraded, it creates a new rollout & creates a new revisioning named revision 2.

This helps us keep track of the deployment & rollback to a previous version of the deployment if needed.

You can see the revisions & status of the deployment using the command

kubectl rollout status deployment/{deployment-name}

to view the history of deployments and revisions use the command

kubectl rollout history deployment/{deployment-name}

The default deployment strategy is a rolling update with Kubernetes.

kubectl apply -f {file-name.yml}is used to update the deployments

kubectl rollout status deployment/{deployment-name} is used to see the status of rollout

kubectl rollout undo deployment/{deployment-name} is used to rollout a deployment.