Guess my number with Kafka

Intro

This is a small Java Spring Boot application demonstration how to use Kafka in your applications. The Kafka broker is set up for local development by using corresponding docker containers.

This application implements the "Guess my number" game. Clients are in competition to find the number as quick as possible. Communication is done via Kafka events/topics.

Setup Docker/Kafka

• Make sure you have installed Docker; e.g. install Docker Desktop: https://www.docker.com/products/docker-desktop/
• Start the Docker containers for Zookeeper and Kafka by going in the folder ./docker and starting docker compose up -d
  • (For redundancy two containers are started for each service (2x Zookeeper + 2x Kafka)) --> commented out per default
  • Background information regarding Docker and Kafka can be found here: kafka-docker-setup
  • Test access to the Kafka container. For example using the Big Data Tools from IntelliJ connecting to localhost:29092
  • Test that Zookeeper is running on port 22181; e.g. use another IntelliJ Plugin like zoolytic

Hello-World application

Just run the application without arguments. It publishes five events to the demoTopic and a consumer is logging those events into the console.

Optional: Inside Kafka - Check topics (using Kafka tools inside the docker-container)

• List all topics: kafka-topics --bootstrap-server kafka-1:9092 --list
• Delete a topic: kafka-topics --bootstrap-server kafka-1:9092 --delete --topic name
• Show config of special topics: kafka-topics --bootstrap-server kafka-1:9092 --describe --topics-with-overrides
• Read/ Replay / list events of the demoTopic: kafka-console-consumer --bootstrap-server kafka-1:9092 --topic demoTopic --from-beginning
• Delete topic (events): kafka-topics --bootstrap-server kafka-1:9092 --delete --topic demoTopic
• Write events to a topic: kafka-console-producer --bootstrap-server kafka-1:9092 --topic guessNumberTopic
• Read events from a topic: kafka-console-consumer --bootstrap-server kafka-1:9092 --topic feedbackNumberTopic

Run GuessNumber application

1. Run one NumberIssuer-App. There should be just one instance. It is responsible for publishing a random number and evaluating the answers of the Guessers. Class com.mos.kafka.kafkaguessnumber.KafkaGuessNumberApplication in profile numberIssuer

2. Run as many NumberGuesser instances as you like. Each of them is guessing the number. The feedback of the Issuer would be: <, >, Matched or Inactive. Start the same main class KafkaGuessNumberApplication with the profile numberGuesser

The Issuer and Guesser are communication via Kafka topics (see also next section). Notice the logs that show you what's going on and which Guesser instance is winning a challenge.

Guesser log: Issuer log:

How it works

The Issuer and Guessers are communicating by using three different topics. The following diagramm summarizes the architecture:

Check also class GlobalDefs for global definitions.