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 Merged File
Consider this lesson a short intermezzo. We'll merge the definitions we used in this chapter into a single YAML file. 

You already had a similar example before, so there's no need for lengthy explanations.

apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: go-demo-2-db
  labels:
    type: db
    service: go-demo-2
    vendor: MongoLabs
spec:
  selector:
    matchLabels:
      type: db
      service: go-demo-2
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        type: db
        service: go-demo-2
        vendor: MongoLabs
    spec:
      containers:
      - name: db
        image: mongo:3.3

---

apiVersion: v1
kind: Service
metadata:
  name: go-demo-2-db
spec:
  ports:
  - port: 27017
  selector:
    type: db
    service: go-demo-2

---

apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: go-demo-2-api
  labels:
    type: api
    service: go-demo-2
    language: go
spec:
  replicas: 3
  selector:
    matchLabels:
      type: api
      service: go-demo-2
  template:
    metadata:
      labels:
        type: api
        service: go-demo-2
        language: go
    spec:
      containers:
      - name: api
        image: vfarcic/go-demo-2
        env:
        - name: DB
          value: go-demo-2-db
        readinessProbe:
          httpGet:
            path: /demo/hello
            port: 8080
          periodSeconds: 1
        livenessProbe:
          httpGet:
            path: /demo/hello
            port: 8080

---

apiVersion: v1
kind: Service
metadata:
  name: go-demo-2-api
spec:
  type: NodePort
  ports:
  - port: 8080
  selector:
    type: api
    service: go-demo-2


# The Differences
If you start searching for differences with the previous definitions, you will find a few. 

* The `minReadySeconds`, `progressDeadlineSeconds`, `revisionHistoryLimit`, and `strategy` fields are removed from the `go-demo-2-api` Deployment. 


* We used them mostly as a way to demonstrate their usage. But, since Kubernetes has sensible defaults, we omitted them from this definition.

* You'll also notice that there are two Services even though we created only one in this chapter. We did not need the `go-demo-2-api` Service in our examples since we didn't need to access the API. But, for the sake of completeness, it is included in this definition. 
* Finally, the strategy for deploying the database is set to `recreate`. As explained earlier, it is more suited for a single-replica database, even though we did not mount a volume that would preserve the data.

# Creating Objects with the Merged File
Let's create the objects defined in `deploy/go-demo-2.yml`. Remember, with `--save-config` we're making sure we can edit the configuration later. The alternative would be to use `kubectl apply` instead.

In this lesson, we will merge all the definitions explored until now into a single YAML file and then create objects using that file.

Merging Everything into the Same YAML Definition

Looking into the Merged File