Run apps on Kubernetes with Spring Cloud Kubernetes

This project shows how to use Spring Cloud Kubernetes to run a Java app on Kubernetes. Thanks to the abstraction provided by Spring, the app source code does not have any dependencies on Kubernetes API: Spring Cloud Kubernetes takes care of integrating the app with Kubernetes features, such as service discovery and configuration using ConfigMap objects. Spring Cloud Kubernetes also provides support for client-side load balancing and circuit breaker patterns.

Source code does not depend on Kubernetes at all, just plain Spring stuff. See for example the backend source code:

import com.fasterxml.jackson.annotation.JsonInclude;
import lombok.Data;
import lombok.RequiredArgsConstructor;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.annotation.PostConstruct;
import java.net.InetAddress;
import java.net.UnknownHostException;

@SpringBootApplication
@EnableDiscoveryClient
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

@Data
@Configuration
@ConfigurationProperties(prefix = "backend")
class AppProperties {
    // These configuration properties are reloaded when the ConfigMap is updated.

    private String message = "Hello world!";
}

@RestController
@RequiredArgsConstructor
class HelloController {
    private final AppProperties props;
    private String hostName;

    @PostConstruct
    public void init() throws UnknownHostException {
        // Get host name once this bean is initialized.
        hostName = InetAddress.getLocalHost().getCanonicalHostName();
    }

    @GetMapping("/")
    public HelloResponse hello() {
        final HelloResponse resp = new HelloResponse();
        resp.setMessage(props.getMessage());
        resp.setSource(hostName);
        return resp;
    }
}

@Data
@JsonInclude(JsonInclude.Include.NON_EMPTY)
class HelloResponse {
    private String message;
    private String source;
}

How to use it?

This repository contains 2 apps: a backend and a frontend.

Note there is no Dockerfile available in this repository. Cloud Native Buildpacks are used to build and package each app into a fully secure & optimized Docker image,

Run this command to create a Docker image for each app:

$ pack build alexandreroman/hello-spring-k8s-backend \
  --path backend
$ pack build alexandreroman/hello-spring-k8s-frontend \
  --path frontend

You can see how these Docker images are created:

• a JDK is provided for compilation
• Maven is downloaded, as well as all project dependencies (about half the Internet 😉)
• source code is compiled and packaged with a JRE
• app artifact is optimized for runtime execution (no root user, dependencies flattened in a directory, different image layers for caching purpose, etc.)

Deploy to a Kubernetes cluster

Run this command to deploy these Docker images to your cluster:

$ kubectl apply -f k8s
namespace/hello-spring-k8s created
configmap/backend created
deployment.apps/backend created
deployment.apps/frontend created
service/frontend created
service/backend created
clusterrole.rbac.authorization.k8s.io/service-discovery-client created
rolebinding.rbac.authorization.k8s.io/default:service-discovery-client created

Check the LoadBalancer allocated IP address to get the public app endpoint:

$ kubectl -n hello-spring-k8s get svc frontend
NAME          TYPE           CLUSTER-IP     EXTERNAL-IP   PORT(S)        AGE
frontend      LoadBalancer   10.97.52.148   X.X.X.X       80:32686/TCP   110s

Scale out the backend app, and see service discovery and client-side load balancing in action:

$ kubectl -n hello-spring-k8s scale --replicas=3 deployment backend
deployment.extensions/backend scaled
$ kubectl -n hello-spring-k8s get pods
NAME                       READY   STATUS    RESTARTS   AGE
backend-9f8b55656-7nvxf    0/1     Running   0          18s
backend-9f8b55656-nxlfv    0/1     Running   0          18s
backend-9f8b55656-w5f4t    1/1     Running   0          4m34s
frontend-8757b7848-sghcb   1/1     Running   0          4m34s

Edit the backend configuration using a ConfigMap object, and check out how the new configuration is applied:

$ kubectl -n hello-spring-k8s edit configmap backend
configmap/backend edited

Contribute

Contributions are always welcome!

Feel free to open issues & send PR.

License

Copyright © 2020 VMware, Inc.

This project is licensed under the Apache Software License version 2.0.