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KAFKA.md

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Java Template Tutorial

This file provides example commands which can be used to run the Java Template publisher/subscriber model using Apache Kafka and a provided YAML file.

Prerequisites

Run Apache Kafka

You will need a running Apache Kafka cluster. Instructions for how to run Kafka can be found here If you are new to Kafka, or want a refresher, you can click here.

Install Maven

For instructions on installing maven for your operating system, please see the Apache Maven site.

Install the AsyncAPI Generator

This template must be used with the AsyncAPI Generator, if you have not already installed the Generator, run:

npm install -g @asyncapi/generator

Set up your Working Environment

To work with the Java Template, you will need to clone the repository. Navigate to a directory where you would like to store the code, for example run

mkdir ~/asyncapi-java-tutorial

You will then need to enter the directory you have just created, for example with

cd ~/asyncapi-java-tutorial

Running the Publisher/Subscriber Template

These commands will allow you to run the Java Template publisher/subscriber model using IBM MQ.

  1. Run the AsyncAPI Generator. 
    ag https://ibm.biz/kafka-asyncapi-yml-sample @asyncapi/java-template -o ./output -p server=production
    Note: The syntax of the above command is shown below. You do not need to run the below line, it is for informational purposes only. 
    ag [YAML_FILE] [TEMPLATE_DIRECTORY] -o ./output -p server=[NAME_OF_SERVER] -p user=[KAFKA_USERNAME] -p password=[KAFKA_PASSWORD]
  2. Navigate to the generated output directory 
    cd output
  3. Install the dependencies required to run this template 
    mvn compile
  4. Create .jar package using maven 
    mvn package
  5. Run your generated Subscriber 
    java -cp target/asyncapi-java-generator-0.1.0.jar com.asyncapi.DemoSubscriber
  6. In a separate terminal, navigate to the output directory above and run your generated Publisher 
    cd ~/asyncapi-java-tutorial/output
java -cp target/asyncapi-java-generator-0.1.0.jar com.asyncapi.DemoProducer

The messages will now be seen to be being sent from the running publisher to the running subscriber, using Kafka topics. Your output from your subscriber should look something like

Oct 14, 2021 9:53:23 AM com.asyncapi.SingleReleasedSubscriber receive
INFO: Received message: {
  “title” : “Hackathon”,
  “artist” : “Java”,
  “album” : “JMS”,
  “genre” : “Java”,
  “length” : 166
}
TYPE: com.asyncapi.models.Single

Running with Docker

To deploy a dockerised instance of this project;

  1. Build the image

     docker build -t [PACKAGE_NAME]:[VERSION] .

  2. Run the image in detached mode

     docker run -d [PACKAGE_NAME]:[VERSION]

Please note; The default Dockerfile included in output will only run DemoSubscriber.java. This will need to be replaced with the entrypoint to your application.

Networking

Docker networking needs to be properly configured in order to allow your project to connect to a Kafka cluster.

If Kafka is also running in a docker container

  1. Create a docker network 
     docker network create exampleKafkaNetwork
  2. Attach the docker network to your Kafka container 
     docker network connect exampleKafkaNetwork
  3. Update your env.json server hostname to match the container name for Kafka. To find the name run 
    docker ps