Kubernetes- Deployment

- Defines how to deploy application in production environment.

Scenarios

• Old instance running - Multiple Pod having applications are running in production environment.
• New version of application is available - need to upgrade seamlessly- without any downtime.
• Rolling update
• For this we don't want to upgrade all of them at once as this may impact accessibility. 
• One by one upgrade - And we might want to upgrade one after other.
• In case of failure - we should be able to rollback the upgrade.
• Multiple change to environment - 
• Ex - Scaling the environment, Modifying resource allocation etc.
• And this change should be done for all PODS together and then activated for all Pods as the same time.

Kubernetes Deployment

• Comes at the top of the hierarchy.
• Comes at top of Pod and Replica Set.

• Available with
• Rolling update
• Undo changes
• Pause changes
• Resume changes

How to create deployment

Yaml file 

• same as ReplicaSet except for change in KIND.

apiVersion: apps/v1   

kind: Deployment      << Only change done for Deployment

metadata:

  name: myapp-replicaset

  labels:

    app: myapp

    type: front-end

spec:

  template:   <<< Here need to provide template for POD. We just to insert metadata + spec section of POD.

    metadata:

      name: myapp-pod

      labels:

        app: myapp

        type: front-end

    

    spec:   

      containers: 

        name: nginx-container

        image: nginx

  replicas: 3   <<< This is sibling of template

  selector:        

    matchLabels:

      type: front-end

Commands