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 ${TARGET}!". If
TARGET is not specified, it will use "World" as the TARGET.
- A Kubernetes cluster with Knative installed. Follow the installation instructions if you need to create one.
- Docker installed and running on your local machine, and a Docker Hub account configured (we'll use it for a container registry).
- You have installed Java SE 8 or later JDK.
While you can clone all of the code from this directory, hello world apps are generally more useful if you build them step-by-step. The following instructions recreate the source files from this folder.
-
From the console, create a new empty web project using the curl and unzip commands:
curl https://start.spring.io/starter.zip \ -d dependencies=web \ -d name=helloworld \ -d artifactId=helloworld \ -o helloworld.zip unzip helloworld.zip
If you don't have curl installed, you can accomplish the same by visiting the Spring Initializr page. Specify Artifact as
helloworld
and add theWeb
dependency. Then clickGenerate Project
, download and unzip the sample archive. -
Update the
SpringBootApplication
class insrc/main/java/com/example/helloworld/HelloworldApplication.java
by adding a@RestController
to handle the "/" mapping and also add a@Value
field to provide the TARGET environment variable:package com.example.helloworld; import org.springframework.beans.factory.annotation.Value; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RestController; @SpringBootApplication public class HelloworldApplication { @Value("${TARGET:World}") String target; @RestController class HelloworldController { @GetMapping("/") String hello() { return "Hello " + target + "!"; } } public static void main(String[] args) { SpringApplication.run(HelloworldApplication.class, args); } }
-
Run the application locally:
./mvnw package && java -jar target/helloworld-0.0.1-SNAPSHOT.jar
Go to
http://localhost:8080/
to see yourHello World!
message. -
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. For additional information on multi-stage docker builds for Java see Creating Smaller Java Image using Docker Multi-stage Build.# Use the official maven/Java 8 image to create a build artifact. # https://hub.docker.com/_/maven FROM maven:3.5-jdk-8-alpine as builder # Copy local code to the container image. WORKDIR /app COPY pom.xml . COPY src ./src # Build a release artifact. RUN mvn package -DskipTests # Use the Official OpenJDK image for a lean production stage of our multi-stage build. # https://hub.docker.com/_/openjdk # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds FROM openjdk:8-jre-alpine # Copy the jar to the production image from the builder stage. COPY --from=builder /app/target/helloworld-*.jar /helloworld.jar # Service must listen to $PORT environment variable. # This default value facilitates local development. ENV PORT 8080 # Run the web service on container startup. CMD ["java","-Djava.security.egd=file:/dev/./urandom","-Dserver.port=${PORT}","-jar","/helloworld.jar"]
-
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.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"
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.
-
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:# Build the container on your local machine docker build -t {username}/helloworld-java . # Push the container to docker registry docker push {username}/helloworld-java
-
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 usingkubectl
:kubectl apply --filename service.yaml
-
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 balancer for your app.
- Automatically scale your pods up and down (including to zero active pods).
-
To find the IP address for your service, use. If your cluster is new, it may take sometime for the service to get asssigned an external IP address.
# In Knative 0.2.x and prior versions, the `knative-ingressgateway` service was used instead of `istio-ingressgateway`. INGRESSGATEWAY=knative-ingressgateway # The use of `knative-ingressgateway` is deprecated in Knative v0.3.x. # Use `istio-ingressgateway` instead, since `knative-ingressgateway` # will be removed in Knative v0.4. if kubectl get configmap config-istio -n knative-serving &> /dev/null; then INGRESSGATEWAY=istio-ingressgateway fi kubectl get svc $INGRESSGATEWAY --namespace istio-system NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE xxxxxxx-ingressgateway LoadBalancer 10.23.247.74 35.203.155.229 80:32380/TCP,443:32390/TCP,32400:32400/TCP 2d
-
To find the URL for your service, use
kubectl get ksvc helloworld-java \ --output=custom-columns=NAME:.metadata.name,DOMAIN:.status.domain NAME DOMAIN helloworld-java helloworld-java.default.example.com
-
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.curl -H "Host: helloworld-java.default.example.com" http://{IP_ADDRESS} Hello World: Spring Boot Sample v1
To remove the sample app from your cluster, delete the service record:
kubectl delete --filename service.yaml