Hello World - Spark Java Framework

    • A Kubernetes cluster with Knative installed and DNS configured. Follow the installation instructions if you need to create one.
    • 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.

    1. Clone the repo from the following path:

    2. Navigate to the helloworld-java-spark directory

    3. Run the application locally:

      1. ./mvnw package && java -jar target/helloworld-0.0.1-SNAPSHOT-jar-with-dependencies.jar

    4. In your project directory, create a file named Dockerfile and copy the code block below into it. For detailed instructions on dockerizing a Spark Java app, see . For additional information on multi-stage docker builds for Java see Creating Smaller Java Image using Docker Multi-stage Build.

    5. 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.

      1. kind: Service
      2. metadata:
      4.   namespace: default
      5. spec:
      6.   template:
      7.     spec:
      8.       containers:
      9.         - image: docker.io/{username}/helloworld-java

    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:

      1. # Build the container on your local machine
      2. docker build -t {username}/helloworld-java .
      4. # Push the container to docker registry

    3. 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).

    4. To find the URL for your service, use

      1. kubectl get ksvc helloworld-java \
      2.     --output=custom-columns=NAME:.metadata.name,URL:.status.url
      4. NAME                URL
      5. helloworld-java     http://helloworld-java.default.1.2.3.4.xip.io

    5. 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.

      2. Hello World!

    To remove the sample app from your cluster, delete the service record: