Hello World - Eclipse Vert.x

Learn how to deploy a simple web app that is written in Java and uses Eclipse Vert.x. This samples uses Docker to build locally. The app reads in a TARGET env variable and then prints "Hello World: ${TARGET}!". If a value for TARGET is not specified, the "NOT SPECIFIED" default value is used.

Use this sample to walk you through the steps of creating and modifying the sample app, building and pushing your container image to a registry, and then deploying your app to your Knative cluster.

Before you begin

You must meet the following requirements to complete this sample:

A version of the Knative Serving component installed and running on your Kubernetes cluster. Follow the Knative installation instructions if you need to create a Knative cluster.
The following software downloaded and install on your loacal machine:
- Java SE 8 or later JDK.
- Eclipse Vert.x v3.5.4.
- Docker for building and pushing your container image.
- curl to test the sample app after deployment.
A Docker Hub account where you can push your container image.

Tip: You can clone the Knative/docs repo and then modify the source files. Alternatively, learn more by manually creating the files yourself.

Creating and configuring the sample code

To create and configure the source files in the root of your working directory:

Create the pom.xml file:

<project xmlns="http://maven.apache.org/POM/4.0.0"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
                  http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.example.vertx</groupId>
<artifactId>helloworld</artifactId>
<version>1.0.0-SNAPSHOT</version>

<dependencies>
    <dependency>
        <groupId>io.vertx</groupId>
        <artifactId>vertx-core</artifactId>
        <version>${version.vertx}</version>
    </dependency>
    <dependency>
        <groupId>io.vertx</groupId>
        <artifactId>vertx-rx-java2</artifactId>
        <version>${version.vertx}</version>
    </dependency>
</dependencies>

<build>
    <plugins>
        <plugin>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.0</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
            </configuration>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-shade-plugin</artifactId>
            <version>3.2.0</version>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>shade</goal>
                    </goals>
                    <configuration>
                        <transformers>
                            <transformer
                                    implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                <manifestEntries>
                                    <Main-Class>io.vertx.core.Launcher</Main-Class>
                                    <Main-Verticle>com.example.helloworld.HelloWorld</Main-Verticle>
                                </manifestEntries>
                            </transformer>
                        </transformers>
                        <artifactSet/>
                    </configuration>
                </execution>
            </executions>
        </plugin>

    </plugins>
</build>
<properties>
    <version.vertx>3.5.4</version.vertx>
</properties>
</project>

Create the HelloWorld.java file in the src/main/java/com/example/helloworld directory. The [ROOT]/src/main/java/com/example/helloworld/HelloWorld.java file creates a basic web server that listens on port 8080.

 package com.example.helloworld;

 import io.reactivex.Flowable;
 import io.vertx.reactivex.core.AbstractVerticle;
 import io.vertx.reactivex.core.http.HttpServer;
 import io.vertx.reactivex.core.http.HttpServerRequest;

 public class HelloWorld extends AbstractVerticle {

     public void start() {

         final HttpServer server = vertx.createHttpServer();
         final Flowable<HttpServerRequest> requestFlowable = server.requestStream().toFlowable();

         requestFlowable.subscribe(httpServerRequest -> {

             String target = System.getenv("TARGET");
             if (target == null) {
                 target = "NOT SPECIFIED";
             }

             httpServerRequest.response().setChunked(true)
                     .putHeader("content-type", "text/plain")
                     .setStatusCode(200) // OK
                     .end("Hello World: " + target);
         });

         server.listen(8080);
     }
 }

Create the Dockerfile file:

# Use fabric8's s2i Builder image.
# https://hub.docker.com/r/fabric8/s2i-java
FROM fabric8/s2i-java:2.0

# Copy the JAR file to the deployment directory.
ENV JAVA_APP_DIR=/deployments
COPY target/helloworld-1.0.0-SNAPSHOT.jar /deployments/

Create the service.yaml file. You must specify your Docker Hub username in {username}. You can also configure the TARGET, for example you can modify the Eclipse Vert.x Sample v1 value.

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: helloworld-vertx
  namespace: default
spec:
  template:
    spec:
      containers:
        - image: docker.io/{username}/helloworld-vertx
          env:
            - name: TARGET
              value: "Eclipse Vert.x Sample v1"

Building and deploying the sample

To build a container image, push your image to the registry, and then deploy your sample app to your cluster:

Use Docker to build your container image and then push that image to your Docker Hub registry. You must replace the {username} variables in the following commands with your Docker Hub username.
```
# Build and push the container on your local machine.
docker buildx build --platform linux/arm64,linux/amd64 -t "{username}/helloworld-vertx" --push .
```
Now that your container image is in the registry, you can deploy it to your Knative cluster by running the kubectl apply command:
```
kubectl apply --filename service.yaml
```
Result: A service name helloworld-vertx is created in your cluster along with the following resources:
- A new immutable revision for the version of the app that you just deployed.
- The following networking resources are created for your app:
  - route
  - ingress
  - service
  - load balancer
- Auto scaling is enable to allow your pods to scale up to meet traffic, and also back down to zero when there is no traffic.

Testing the sample app

To verify that your sample app has been successfully deployed:

Retrieve the URL for your service, by running the following kubectl get command:

kubectl get ksvc helloworld-vertx  --output=custom-columns=NAME:.metadata.name,URL:.status.url

Example result:

NAME                URL
helloworld-vertx    http://helloworld-vertx.default.1.2.3.4.sslip.io

Now you can make a request to your app and see the result. Replace the URL below with the URL returned in the previous command.
```
curl http://helloworld-vertx.default.1.2.3.4.sslip.io
```
Example result:
```
 Hello World: Eclipse Vert.x Sample v1
```

Congratulations on deploying your sample Java app to Knative!

Removing the sample app deployment

To remove the sample app from your cluster, run the following kubectl delete command:

kubectl delete --filename service.yaml