Kubernetes - First Microservice (step by step)

The Project’s Structure:

Our? DemoApplication.java is the entry point of the application:

package com.example.demo;
	

	import org.springframework.boot.SpringApplication;
	import org.springframework.boot.autoconfigure.SpringBootApplication;
	

	@SpringBootApplication
	public class DemoApplication {
	

	    public static void main(String[] args) {
	        SpringApplication.run(DemoApplication.class, args);
	    }
	

	}        

The code above contains the minimal lines needed to create a Spring Boot application.

The?HelloWorldCtrl.java contains a simple controller that maps the root path?(“/”) and returns a greeting String:

package com.example.demo;
	

	import org.springframework.web.bind.annotation.RestController;
	import org.springframework.web.bind.annotation.RequestMapping;
	

	@RestController
	public class HelloWorldCtrl {
	

	    @RequestMapping("/")
	    public String index() {
	        return "Greetings from Spring Boot!";
	    }
	

	}        

Creating K8s Resources

In order to create a K8s deployment, we’ll need a Docker image. Let’s add the following lines to our?Dockerfile :

FROM openjdk:12

EXPOSE 8080

COPY target/*.jar /opt/app.jar

WORKDIR /opt

ENTRYPOINT exec java $JAVA_OPTS -jar app.jar        

before building the image, we have to build the application using mvn, then we can build the image and push to the hub:

docker build -t hamoshka/demo .
docker push hamoshka/demo        

The K8s resources which we will use in our example are a?deployment?and a?service:

i recommend to create directory /kube under the project to put all k8s resources together.

our first resource we will use is the demo-deployment.yaml

apiVersion: apps/v

kind: Deployment

metadata:

? name: demo-deployment

? labels:

? ? app: demo

spec:

? replicas: 3

? selector:

? ? matchLabels:

? ? ? app: demo

? template:

? ? metadata:

? ? ? labels:

? ? ? ? app: demo

? ? spec:

? ? ? containers:

? ? ? - name: demo

? ? ? ? image: hamoshka/demo

? ? ? ? ports:

? ? ? ? - containerPort: 8080        

The deployment defines 3 replicas of the pod that will be running the container that’s built from the image specified in the image attribute (hamoshka/demo).

Creating the resources in your cluster:

kubectl create -f /kube/demo-deployment.yaml
        

our second resource we will use is the service demo-loadbalancer.yaml

we will use the service type loadbalancer to make our pods accessible from outside the cluster.

apiVersion: v1

kind: Service

metadata:

? name: demo

? namespace: default

spec:

? allocateLoadBalancerNodePorts: true

? externalTrafficPolicy: Cluster

? internalTrafficPolicy: Cluster

? ipFamilies:

? - IPv4

? ipFamilyPolicy: SingleStack

? ports:

? - nodePort:?

? ? port: 80

? ? protocol: TCP

? ? targetPort: 8080

? selector:

? ? app: demo

? sessionAffinity: None

? type: LoadBalancer

status:

? loadBalancer:

? ? ingress:

? ? - hostname: localhost        

then we have to create the resource using kubectl .

kubectl create -f /kube/demo-loadbalancer.yaml        

now we are done, just test it from your browser: