Kubernetes is a powerful tool. It can help you manage complex applications and provide you with the ability to easily automate tasks involved in managing them. In this course, we will start exploring Kubernetes from a beginner's standpoint. We will discuss what Kubernetes is and what it does, and we will work with some of the basic functionality of Kubernetes hands-on. We will build a simple Kubernetes cluster. We will also deploy a sample microservice application to the cluster in order to explore how Kubernetes can help easily manage such applications.

A Practical Guide to Kubernetes

# Looking into the Definition

Let's take a look at a ReplicaSet definition for a Pod with only the database.

apiVersion: apps/v1beta2
kind: ReplicaSet
metadata:
  name: go-demo-2-db
spec:
  selector:
    matchLabels:
      type: db
      service: go-demo-2
  template:
    metadata:
      labels:
        type: db
        service: go-demo-2
        vendor: MongoLabs
    spec:
      containers:
      - name: db
        image: mongo:3.3
        ports:
        - containerPort: 28017

We'll comment only on the things that changed.

Since this ReplicaSet defines only the database, we reduced the number of replicas to `1`. Truth be told, MongoDB should be scaled as well, but that's out of the scope of this chapter. For now, we'll pretend that one replica of a database is enough.

Since `selector` labels need to be unique, we changed them slightly. The `service` is still `go-demo-2`, but the `type` was changed to `db`.

The rest of the definition is the same except that the `containers` now contain only `mongo`. We'll define the API in a separate ReplicaSet.

# Creating the ReplicaSet
Let's create the ReplicaSet before we move to the Service that will reference its Pod.

In this lesson, we will split up the Pods, create a separate DB pod and a Service to communicate with it.

Splitting the Pod and Establishing Communication through Services

Looking into the Definition