Kubernetes 101 - Practical

Deployment Object

This is one of the key objects in Kubernetes. Because our ultimate goal is to create pod objects in K8s. But we will not create pods directly, rather we will create deployment objects and provide instructions to create the number of pods (and containers) that need to be created.

If we look into the official documentation, we will find some guidelines on how to write deployment configuration. Here on the right, we have a deployment object to create a deployment of a simple spring boot application container. You can prepare your docker image and replace the shikhorroy/simple-spring-boot-app:0.0.1 image under containers.

Now run the following command to create a deployment:

kubectl apply -f deployment.yaml

Service Object

If we want to access the deployed application (in a pod) outside the Kubernetes cluster we need a service.

Here is the Service Object official documentation.

On the right side, I created one service object. The points that need to be cared for are the selector in service, and the matcheLabels in deployment should be matched with the label in template metadata.

Run the following command to create a service:

kubectl apply -f service.yaml

To access the application from the browser, you can run the following if you are using minikube for the local environment:

minikube service myapp-service

This will open the accessible URL in the browser and also show output like (for your case this will vary) this:

|-----------|---------------|-------------|---------------------------|
| NAMESPACE |     NAME      | TARGET PORT |            URL            |
|-----------|---------------|-------------|---------------------------|
| default   | myapp-service |        8080 | http://192.168.49.2:30193 |
|-----------|---------------|-------------|---------------------------|
* Starting tunnel for service myapp-service.
|-----------|---------------|-------------|------------------------|
| NAMESPACE |     NAME      | TARGET PORT |          URL           |
|-----------|---------------|-------------|------------------------|
| default   | myapp-service |             | http://127.0.0.1:63187 |
|-----------|---------------|-------------|------------------------|

So manually we can hit: http://127.0.0.1:63187 to access the deployed application.

K8s Declarative Object Configurations

deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
        - name: myapp-java
          image: shikhorroy/simple-spring-boot-app:0.0.1
          imagePullPolicy: IfNotPresent
          ports:
            - containerPort: 8080

service.yaml

apiVersion: v1
kind: Service
metadata:
  name: myapp-service
spec:
  selector:
    app: myapp
  ports:
    - protocol: TCP
      port: 8080
      targetPort: 8080
  type: LoadBalancer