Distributed Transactions in Ballerina

This repository contains a distributed transaction example implemented using Ballerina, showcasing how to coordinate transactions across multiple microservices. The example implementation is a simple e-commerce platform that handles inventory updates, payment processing, and user notifications.

How It Works

1. Place Order: When an order is placed through the order service, it initiates a transaction.
2. Transaction Coordination: Within the transaction, the order service interacts with the payment service and the inventory service.
3. Payment Verification: The order service verifies the payment by calling the payment service.
4. Inventory Update: Simultaneously, it updates the inventory by calling the inventory service.
5. Commit/Rollback: If all operations are successful, the transaction commits, ensuring the order is completed. Otherwise, it rolls back, ensuring data consistency.

Services

Service	Service Path	Port	Description
Order Service	/	9650	Manages order placement and coordinates with the payment and inventory services for order completion.
Payment Service	/payment	9651	Handles payment transactions and interacts with a MySQL database for payment validation and updates.
Inventory Service	/inventory	9652	Manages inventory, ensures item availability, and updates inventory status after order placement.

Usage

Pre-requisists

Create necessary databases, tables and add configurations in Config.toml files.

• Run 2 database (MySQL) instances on separate docker containers.

  docker run -e MYSQL_ROOT_PASSWORD=<password> -p <PORT>:3306 -d mysql
  

• Create Stock table.

  CREATE TABLE IF NOT EXISTS Stock (
      itemId INT PRIMARY KEY,
      amount INT,
      unitPrice INT
  );
  

• Create Payments table.

  CREATE TABLE IF NOT EXISTS Payments (
      `cardno` VARCHAR(16) NOT NULL PRIMARY KEY,
      `amount` INT NOT NULL
  );
  

Populate both tables with dummy data.

INSERT INTO `Stock`
    (`itemId`, `amount`, `unitPrice`)
    VALUES
    (1, 100, 20),
    (2, 150, 25),
    (3, 200, 18),
    (4, 10, 60);

INSERT INTO `Payments`
    (`cardno`, `amount`)
    VALUES
    ('card1', 1000),
    ('card2', 2000),
    ('card3', 5000);

Running the Example

1. Run the payment, inventory and order services using bal run command.
2. Try it out by sending a post request to placeOrder endpoint on port 9650 with a OrderRequest ({ cardNo='', itemId='', qty='' }).

Sequence Diagram

sequenceDiagram
    participant OrderService
    participant Coordinator
    participant PaymentService
    participant InventoryService
 
        OrderService->>Coordinator: Begin Transaction
        Coordinator->PaymentService: Register participant for txn
        Coordinator->InventoryService: Register participant for txn
    
    OrderService->>Coordinator: Make Payment
    Coordinator->>PaymentService: Do Payment
    OrderService->>Coordinator: Update Inventory
    Coordinator->>InventoryService: Update Inventory


    PaymentService-->>Coordinator: Payment Response
    InventoryService-->>Coordinator: Inventory Update Response
    
    rect rgba(138,138,138,255)
        Coordinator->>PaymentService: Prepare
        Coordinator->>InventoryService: Prepare
            PaymentService->>Coordinator: Prepared
            InventoryService->>Coordinator: Prepared
    end
    Note over Coordinator: Makes Decision    
    alt Prepare Successful
        Coordinator-->>PaymentService: Commit Payment
        Coordinator-->>InventoryService: Commit Inventory Update
        OrderService->>OrderService: Send Order Confirmation        
        Coordinator-->>OrderService: Transaction Committed
    else Transaction / Prepare Failed
        Coordinator-->>PaymentService: Rollback Payment
        Coordinator-->>InventoryService: Rollback Inventory Update
        Coordinator-->>OrderService: Transaction Rolled Back
    end
    Coordinator->>OrderService: End Transaction
    

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Tech Stack

1. Ballerina
2. MySQL Databases