# Hello World - Spring Boot Java sample A simple web app written in Java using Spring Boot 2.0 that you can use for testing. It reads in an env variable `TARGET` and prints "Hello World: ${TARGET}!". If TARGET is not specified, it will use "NOT SPECIFIED" as the TARGET. ## Prerequisites * A Kubernetes cluster with Knative installed. Follow the [installation instructions](https://github.com/knative/install/) if you need to create one. * [Docker](https://www.docker.com) installed and running on your local machine, and a Docker Hub account configured (we'll use it for a container registry). * You have installed [Java SE 8 or later JDK](http://www.oracle.com/technetwork/java/javase/downloads/index.html). ## Recreating the sample code While you can clone all of the code from this directory, hello world apps are generally more useful if you build them step-by-step. The following instructions recreate the source files from this folder. 1. From the console, create a new empty web project using the curl and unzip commands: ```shell curl https://start.spring.io/starter.zip \ -d dependencies=web \ -d name=helloworld \ -d artifactId=helloworld \ -o helloworld.zip unzip helloworld.zip ``` If you don't have curl installed, you can accomplish the same by visiting the [Spring Initializr](https://start.spring.io/) page. Specify Artifact as `helloworld` and add the `Web` dependency. Then click `Generate Project`, download and unzip the sample archive. 1. Update the `@SpringBootApplication` class in `src/main/java/com/example/helloworld/HelloworldApplication.java` by adding a `@RestController` to handle the "/" mapping and also add a `@Value` field to provide the TARGET environment variable: ```java package com.example.helloworld; import org.springframework.beans.factory.annotation.Value; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RestController; @SpringBootApplication public class HelloworldApplication { @Value("${TARGET:NOT SPECIFIED}") String target; @RestController class HelloworldController { @GetMapping("/") String hello() { return "Hello World: " + target; } } public static void main(String[] args) { SpringApplication.run(HelloworldApplication.class, args); } } ``` 1. In your project directory, create a file named `Dockerfile` and copy the code block below into it. For detailed instructions on dockerizing a Spring Boot app, see [Spring Boot with Docker](https://spring.io/guides/gs/spring-boot-docker/). For additional information on multi-stage docker builds for Java see [Creating Smaller Java Image using Docker Multi-stage Build](http://blog.arungupta.me/smaller-java-image-docker-multi-stage-build/). ```docker FROM maven:3.5-jdk-8-alpine as build ADD pom.xml ./pom.xml ADD src ./src RUN mvn package -DskipTests FROM openjdk:8-jre-alpine COPY --from=build /target/helloworld-*.jar /helloworld.jar VOLUME /tmp ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/helloworld.jar"] ``` 1. Create a new file, `service.yaml` and copy the following service definition into the file. Make sure to replace `{username}` with your Docker Hub username. ```yaml apiVersion: serving.knative.dev/v1alpha1 kind: Service metadata: name: helloworld-java namespace: default spec: runLatest: configuration: revisionTemplate: spec: container: image: docker.io/{username}/helloworld-java env: - name: TARGET value: "Spring Boot Sample v1" ``` ## Building and deploying the sample Once you have recreated the sample code files (or used the files in the sample folder) you're ready to build and deploy the sample app. 1. Use Docker to build the sample code into a container. To build and push with Docker Hub, run these commands replacing `{username}` with your Docker Hub username: ```shell # Build the container on your local machine docker build -t {username}/helloworld-java . # Push the container to docker registry docker push {username}/helloworld-java ``` 1. After the build has completed and the container is pushed to docker hub, you can deploy the app into your cluster. Ensure that the container image value in `service.yaml` matches the container you built in the previous step. Apply the configuration using `kubectl`: ```shell kubectl apply -f service.yaml ``` 1. Now that your service is created, Knative will perform the following steps: * Create a new immutable revision for this version of the app. * Network programming to create a route, ingress, service, and load balance for your app. * Automatically scale your pods up and down (including to zero active pods). 1. To find the IP address for your service, use `kubectl get svc knative-ingressgateway -n istio-system` to get the ingress IP for your cluster. If your cluster is new, it may take sometime for the service to get asssigned an external IP address. ```shell kubectl get svc knative-ingressgateway -n istio-system NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE knative-ingressgateway LoadBalancer 10.23.247.74 35.203.155.229 80:32380/TCP,443:32390/TCP,32400:32400/TCP 2d ``` 1. To find the URL for your service, use ``` kubectl get services.serving.knative.dev helloworld-java -o=custom-columns=NAME:.metadata.name,DOMAIN:.status.domain NAME DOMAIN helloworld-java helloworld-java.default.example.com ``` 1. Now you can make a request to your app to see the result. Replace `{IP_ADDRESS}` with the address you see returned in the previous step. ```shell curl -H "Host: helloworld-java.default.example.com" http://{IP_ADDRESS} Hello World: Spring Boot Sample v1 ``` ## Removing the sample app deployment To remove the sample app from your cluster, delete the service record: ```shell kubectl delete -f service.yaml ```