Kafka Demo Application

This repository contains two Spring Boot applications that demonstrate Kafka messaging between microservices:

• kafka-producer: Service that sends messages to Kafka

• kafka-consumer: Service that consumes messages from Kafka

Architecture

HTTP Client → kafka-producer (POST /kafka/send) → Kafka Topic → kafka-consumer

Prerequisites

• Java 17+
• Spring Boot 3+
• Maven
• Docker and Docker Compose
• Kafka (local installation or via Docker)

Quick Start

Option 1: Using Local Kafka Installation

1. Install and start Kafka locally: https://kafka.apache.org/downloads

2. Configure .environment. Use variables .environment_example from resources of app (producer/consumer)

3. Start the applications locally

Option 2: Using Docker Compose (Recommended)

1. Start Kafka with Docker Compose:

cd docker-compose-kafka
docker-compose up -d

2. Configure .environment. Use variables from file .environment_example from resources of app ( producer/consumer)

3. Start the applications locally

Option 3: Fully Containerized with Docker Compose

1. Create environment file. Use variables from file .env_example.

2. Form jar files

mvn clean install

3. Start all services

docker-compose up -d

Configuration

Copy the example environment files and configure as needed

For kafka-producer:

cp kafka-producer/src/main/resources/.environment_example kafka-producer/src/main/resources/.env

For kafka-consumer:

cp kafka-consumer/src/main/resources/.environment_example kafka-consumer/src/main/resources/.env

Kafka Configuration

The Kafka topic is automatically created by the producer application with the following configuration:

• Topic name: test-topic

• Partitions: 3

• Replication factor: 1 (for development)

API Usage

Send Message Endpoint: POST /kafka/send

Request:

curl -X POST http://localhost:8080/kafka/send \
-H "Content-Type: application/json" \
-d '{
"message": "My message"
}'

Response:

{
    "status": "Message sent successfully",
    "timestamp": "2025-09-17T12:36:30.6062484"
}

Verify Message Consumption

Check the kafka-consumer application logs to see consumed messages:

2025-09-17T12:36:30.634+03:00  INFO 10440 --- [kafka-consumer] [ntainer#0-0-C-1] c.e.k.consumer.KafkaConsumer             : Received message: {
    "message": "My message"
}

Project Structure

kafka-app/
├── kafka-producer/          # Producer application
│   ├── src/main/java/
│   ├── src/main/resources/
│   └── pom.xml
├── kafka-consumer/          # Consumer application
│   ├── src/main/java/
│   ├── src/main/resources/
│   └── pom.xml
├── docker-compose-kafka/    # Kafka infrastructure
│   └── docker-compose.yml
├── docker-compose.yml       # Main application compose
├── .env_example            # Environment variables template
└── README.md