Distributed Transactions in Reactive Spring with Kafka

This project demonstrates a distributed transaction architecture using Reactive Spring and Kafka. The application consists of two services: order-service and payment-service, and utilizes Kafka events to ensure consistency between them. The order is confirmed only when the payment is successful. If the user doesn't have sufficient balance, the payment-service denies the payment and stores the transaction in db for future reference.

Table of Contents

• Architecture Overview
• Technologies Used
• Setup and Installation
• Internal Flow
• Testing the Application

Architecture Overview

The system consists of the following components:

• Common Dto: Consists of common components in the applicaiton.
• Order Service: Responsible for managing order creation.
• Payment Service: Manages the payment process for orders.

Technologies Used

• Spring Boot for building the services.
• Reactive Spring for non-blocking, reactive programming.
• Apache Kafka for event-driven architecture.
• SQL for storage
• Postman for API testing.

Setup and Installation

1. Clone the repository:

   git clone https://github.com/Ommanimesh2/distributed-transactions-kafka.git
   cd distributed-transactions-kafka

2. Build the project: Navigate to the root directory and run the following command:

   mvn clean install

3. Set up Zookeeper and Kafka: Follow the steps below to install and run Kafka and Zookeeper locally:

   • Download and install Apache Kafka from here.
   • Start Zookeeper:

     bin/zookeeper-server-start.sh config/zookeeper.properties

   • Start Kafka broker:

     bin/kafka-server-start.sh config/server.properties

4. Run Order Service: Navigate to the order-service directory and run:

   mvn spring-boot:run

5. Database Setup: Make sure your database is set up with the required tables/collections for order service.

6. Run Payment Service: Navigate to the payment-service directory and run:

   mvn spring-boot:run

7. Import Postman Collection: Import the provided Postman collection to test the application APIs. This collection includes test cases for placing orders and handling payments.

Internal Flow

1. Order Creation:

   • The Order Service is responsible for creating orders. When an order is placed, it produces an order-event and sends it to Kafka.
   • Example request:

     {
       "userId": 2,
       "productId": 3547,
       "price": 1200
     }

2. Order Event Consumption:

   • The Payment Service listens for the order-event from Kafka. Once it consumes the event, it processes the payment based on the user balance and the order amount.

3. Payment Event:

   • Depending on the payment result, the Payment Service produces a payment-event and sends it back to Kafka. This event contains the payment status (SUCCESS, FAILED).
   • Example payment event:

     {
       "userId": 2,
       "productId": 3547,
       "price": 1200,
       "paymentStatus": "FAILED"
     }

4. Order Update:

   • The Order Service consumes the payment-event and updates the order status. If the payment is successful, the order status is marked as COMPLETED. Otherwise, the order is marked as CANCELLED.

   • Success Flow:

     • Payment is successful → orderStatus is updated to COMPLETED.

   • Failure Flow:

     • Payment fails → orderStatus is updated to CANCELLED.

Testing the Application

1. Place an order using the Order Service API:

   • Endpoint: POST /orders/create
   • Example request body:

     {
       "userId": 1,
       "productId": 3923,
       "price": 3000
     }

2. Observe the payment processing in Payment Service, which consumes the order event and produces a payment event based on user balance.

3. Check the order status:

   • If the payment is successful, the order status will be COMPLETED.
   • If the payment fails, the order status will be CANCELLED.

Example Response

1. Order with successful payment:

   {
     "orderId": 3,
     "userId": 2,
     "productId": 3923,
     "price": 3000,
     "paymentStatus": "SUCCESS",
     "orderStatus": "COMPLETED"
   }

2. Order with failed payment:

   {
     "orderId": 2,
     "userId": 1,
     "productId": 3547,
     "price": 1200,
     "paymentStatus": "FAILED",
     "orderStatus": "CANCELLED"
   }