Kubernetes: 3. Deployments

What is Deployment in Kubernetes?

• Deployment is a Kubernetes object
• It is a higher level object, above the replica set
• A Deployment provides declarative updates for Pods and 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.
• A deployment automatically creates the replica set
• Replica set created by deployment should not be managed manually

Uses of Deployment

• Run multiple instances of applications
• Upgrade the docker instances seamlessly - Upgrade one after the other - Rolling updates!
• Rollback the recent changes
• Upgrade the webservers / Scaling the environment / Update the resources - All at a single time
• Pause and Resume the upgrades

deployment-definition.yaml

apiVersion: apps/v1

kind: Deployment

metadata:

    name: myapp-deployment

    labels:

        app: myapp

        type: front-end

spec:

    replicas: 3

    selector:

        matchLabels:

            type: front-end

    template:

        metadata:

            name: myapp-pod

            labels:

                app: myapp

                type: front-end

        spec:

            containers:

            - name: nginx-container

              image: nginx

kubectl create -f deployment-definition.yaml

kubectl get deployment-definition.yaml

kubectl get rs

-> A deployment automatically creates replica set

kubectl get pods

-> Check the pods created by replica set

kubectl get all

-> Get all the objects created by kubernetes in the current namespace

kubectl edit deployment my-deployment

-> Update deployment. Pods are recreated with new template