Nrthugu

Just finished reading Nigel Poulton's The Kubernetes Book. I'm left with the question of whether or not a Deployment can specify multiple ReplicaSets.

When I think Deployment, I think of it in the traditional sense of an entire application being deployed. Or is there meant to be a Deployment for each microservice?

apiVersion: apps/v1beta2

kind: Deployment

metadata: 

  name: hello-deploy

spec:

  replicas: 10

  selector:

    matchLabels:

      app: hello-world

  minReadySeconds: 10

  strategy:

    type: RollingUpdate

    rollingUpdate:

      maxUnavailable: 1

      maxSurge: 1

  template:

    metadata:

      labels:

        app: hello-world

    spec:

      containers:

      - name: hello-pod

        image: nigelpoulton/k8sbook : latest

        ports:

        - containerPort: 8080

It is meant to be a deployment of each microservice.

You can also manage the quantity of "deployed services" of each microservices type.
So for instance, if you want to deploy Service A (Docker image with an Java service) 5 times, you have a deployment resulting 5 pods. Each pod contains the image of Service A.

If you deploy a new version of this Service A (Docker image with an Java service), Kubernetes is able to do a rolling update and manage the shut down of the old Java service type (the existing pods) and creates 5 new pods with the new Java Service A.2 (a new docker image).

Thus your whole microservices application/infrastructure is build upon multiple deployments. Each generating Kubernetes pods, which are published by Kubernetes services.

A deployment contains a single pod template, and generates one replicaset per revision