This guide walks you through the process of deploying a Spring Boot application on Kubernetes. There are many choices of how to do things with Spring Boot and Kubernetes — the intention with this guide is to get you up and running as quickly as possible, not to discuss all the alternatives or go into all the details of how you get to production (which is, of course, our favourite place to be).

There are some interactive tutorials that complement and extend the content of this guide on Katacoda/springguides. If you follow those tutorials, all the code will be running in the cloud from your browser. Or you can create your own cluster and install all the tools you need locally, then copy paste from the guides.

What you’ll build

Kubernetes is an open-source system for automating deployment, scaling, and management of containerized applications. It groups containers that make up an application into logical units for easy management and discovery. In this guide we will build and deploy a simple Spring boot application.

There is also a Getting Started Guide and a Topical Guide on Docker, which cover some of the background on building a container image.

What you’ll need

You will need a Linux or Linux-like command line. Command line examples in this guide work on Linux, a MacOS terminal with a shell, or WSL on Windows.

You will also need a Kubernetes cluster and the command line tool Kubectl. You can create a cluster locally using Kind (on Docker) or Minikube. Or you can use a cloud provider, such as Google Cloud Platform, Amazon Web Services or Microsoft Azure. Before proceeding further, verify you can run kubectl commands from the shell. E.g. (using kind):

$ kubectl cluster-info
Kubernetes master is running at https://127.0.0.1:46253
KubeDNS is running at https://127.0.0.1:46253/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy

To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.

and

$ kubectl get all
NAME                 TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
service/kubernetes   ClusterIP   10.43.0.1    <none>        443/TCP   7m13s

Create a Spring Boot Application

The first thing we will do is create a Spring Boot application. If you have one you prefer to use already in github, you could clone it in the terminal (git and java are installed already). Or you can create an application from scratch using start.spring.io:

curl https://start.spring.io/starter.tgz -d dependencies=webflux,actuator | tar -xzvf -

You can then build the application:

./mvnw install
It will take a couple of minutes the first time, but then once the dependencies are all cached it will be fast.

And you can see the result of the build. If the build was successful, you should see a JAR file, something like this:

ls -l target/*.jar
-rw-r--r-- 1 root root 19463334 Nov 15 11:54 target/demo-0.0.1-SNAPSHOT.jar

The JAR is executable:

$ java -jar target/*.jar

The app has some built in HTTP endpoints by virtue of the "actuator" dependency we added when we downloaded the project. So you will see something like this in the logs on startup:

...
2019-11-15 12:12:35.333  INFO 13912 --- [           main] o.s.b.a.e.web.EndpointLinksResolver      : Exposing 2 endpoint(s) beneath base path '/actuator'
2019-11-15 12:12:36.448  INFO 13912 --- [           main] o.s.b.web.embedded.netty.NettyWebServer  : Netty started on port(s): 8080
...

So you can curl the endpoints in another terminal:

$ curl localhost:8080/actuator | jq .
{
  "_links": {
    "self": {
      "href": "http://localhost:8080/actuator",
      "templated": false
    },
    "health-path": {
      "href": "http://localhost:8080/actuator/health/{*path}",
      "templated": true
    },
    "health": {
      "href": "http://localhost:8080/actuator/health",
      "templated": false
    },
    "info": {
      "href": "http://localhost:8080/actuator/info",
      "templated": false
    }
  }
}

To complete this step, send Ctrl+C to kill the application.

Containerize the Application

There are multiple options for containerizing a Spring Boot application. For local development and testing it makes sense to start with a Dockerfile as the docker build workflow is generally well known and understood.

If you don’t have docker locally or want to automatically push an image to a registry then Jib would be a good choice. In an enterprise setting, when you need a trusted build service for a CI/CD pipeline, you could look at Cloud Native Buildpacks.

First create a Dockerfile:

FROM openjdk:8-jdk-alpine AS builder
WORKDIR target/dependency
ARG APPJAR=target/*.jar
COPY ${APPJAR} app.jar
RUN jar -xf ./app.jar

FROM openjdk:8-jre-alpine
VOLUME /tmp
ARG DEPENDENCY=target/dependency
COPY --from=builder ${DEPENDENCY}/BOOT-INF/lib /app/lib
COPY --from=builder ${DEPENDENCY}/META-INF /app/META-INF
COPY --from=builder ${DEPENDENCY}/BOOT-INF/classes /app
ENTRYPOINT ["java","-cp","app:app/lib/*","com.example.demo.DemoApplication"]

Then build the container image, giving it a tag (choose your own ID instead of "springguides" if you are going to push to Dockerhub):

$ docker build -t springguides/demo .

You can run the container locally:

$ docker run -p 8080:8080 springguides/demo

and check that it works in another terminal:

$ curl localhost:8080/actuator/health

Finish off by killing the container.

You won’t be able to push the image unless you authenticate with Dockerhub (docker login), but there’s an image there already that should work. If you were authenticated you could:

$ docker push springguides/demo

In real life the image needs to be pushed to Dockerhub (or some other accessible repository) because Kubernetes pulls the image from inside its Kubelets (nodes), which are not in general connected to the local docker daemon. For the purposes of this scenario you can omit the push and just use the image that is already there.

Just for testing, there are workarounds that make docker push work with an insecure local registry, for instance, but that is out of scope for this scenario.

Deploy the Application to Kubernetes

You have a container that runs and exposes port 8080, so all you need to make Kubernetes run it is some YAML. To avoid having to look at or edit YAML, for now, you can ask kubectl to generate it for you. The only thing that might vary here is the --image name. If you deployed your container to your own repository, use its tag instead of this one:

$ kubectl create deployment demo --image=springguides/demo --dry-run -o=yaml > deployment.yaml
$ echo --- >> deployment.yaml
$ kubectl create service clusterip demo --tcp=8080:8080 --dry-run -o=yaml >> deployment.yaml

You can take the YAML generated above and edit it if you like, or you can just apply it:

$ kubectl apply -f deployment.yaml
deployment.apps/demo created
service/demo created

Check that the application is running:

$ kubectl get all
NAME                             READY     STATUS      RESTARTS   AGE
pod/demo-658b7f4997-qfw9l        1/1       Running     0          146m

NAME                 TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)    AGE
service/kubernetes   ClusterIP   10.43.0.1       <none>        443/TCP    2d18h
service/demo         ClusterIP   10.43.138.213   <none>        8080/TCP   21h

NAME                   READY     UP-TO-DATE   AVAILABLE   AGE
deployment.apps/demo   1/1       1            1           21h

NAME                              DESIRED   CURRENT   READY     AGE
replicaset.apps/demo-658b7f4997   1         1         1         21h
d
Keep doing kubectl get all until the demo pod shows its status as "Running".

Now you need to be able to connect to the application, which you have exposed as a Service in Kubernetes. One way to do that, which works great at development time, is to create an SSH tunnel:

$ kubectl port-forward svc/demo 8080:8080

then you can verify that the app is running in another terminal:

$ curl localhost:8080/actuator/health
{"status":"UP"}