Running your Spring Boot app on Kubernetes

This project describes how to run your Spring Boot app on Kubernetes. You don't actually need to rewrite your app in order to target a K8s cluster: Spring Boot can run on many platforms, thanks to the abstraction level it provides.

This app is made of a single REST controller:

@RestController
class HelloController {
    @Value("${app.message:Hello world!}")
    private String message;

    @GetMapping(value = "/", produces = MediaType.TEXT_PLAIN_VALUE)
    String greeting() {
        // Just return a simple String.
        return message;
    }
}

How to use it?

Compile this app using a JDK 15+:

$ ./mvnw clean package

You can run this app on your workstation:

$ java -jar target/spring-on-k8s.jar

The app is available at http://localhost:8080:

$ curl localhost:8080
Hello world!%

Creating a Docker image

Our goal is to run this app in a K8s cluster: you first need to package this app in a Docker image.

Use Cloud Native Buildpacks to build & deploy your Docker image:

$ ./mvnw spring-boot:build-image

If you need to use a different image name, please edit pom.xml:

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <configuration>
        <image>
            <name>myrepo/spring-on-k8s</name>
        </image>
    </configuration>
</plugin>

This command will take care of building a Docker image containing a base image, a JRE, and this image will be optimized (unzipped JAR file, different layers for app/config/lib).

As you can see, you don't need a Dockerfile when using Cloud-Native Buildpacks for building a Docker image: that's magic!

Deploying to Kubernetes

This project includes Kubernetes descriptors, so you can easily deploy this app to your favorite K8s cluster:

$ kubectl apply -k k8s/base

Using this command, monitor the allocated IP address for this app:

$ kubectl -n spring-on-k8s get svc
NAME     TYPE           CLUSTER-IP       EXTERNAL-IP     PORT(S)        AGE
app-lb   LoadBalancer   10.100.200.204   35.205.141.26   80:31633/TCP   90s

At some point, you should see an IP address under the column EXTERNAL-IP.

If you hit this address, you will get a greeting message from the app:

$ curl 35.205.141.26
Hello Kubernetes!%

You can also rely on your ingress controller to expose the app. Edit the file k8s/ingress/ingress.yml and set the domain name accordingly.

Then run this command:

kubectl apply -k k8s/ingress

Contribute

Contributions are always welcome!

Feel free to open issues & send PR.

License

Copyright © 2024 Broadcom, Inc. or its affiliates.

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