How to manage distributed transactions in micro-service architecture.
Lets first understand the problem statement:
Overview
Microservice architecture breaks down a monolithic application into smaller, independent services, each with its own database and business logic. This approach enhances scalability, maintainability, and development speed. However, it also introduces significant challenges, particularly in managing transactions that span multiple services, known as distributed transactions.
The Challenge
Managing distributed transactions in a microservice architecture is inherently complex due to the need to maintain data consistency across multiple independent services. Unlike monolithic architectures, where a single transaction can easily ensure ACID (Atomicity, Consistency, Isolation, Durability) properties, microservices must coordinate between distributed databases and services, often leading to issues like partial updates, data inconsistencies, and increased latency.
Example Scenario
Consider an e-commerce platform using a microservice architecture with the following services:
User Story: A customer places an order. The system must:
Steps Involved
Potential Issues
Consequences
Example of Potential Issues
Compensation Logic:
If payment processing fails, the system must reverse the stock deduction and delete the order, which can be complex to implement correctly.
If shipping scheduling fails, the system must reverse the payment and restock the items, ensuring all services are correctly updated.
Till this point I hope you are got the idea about the problem statement, now lets introduce SAGA to solve this problem
The Saga design pattern is a microservices architectural pattern to manage data consistency across distributed services. It's particularly useful in complex transactions that span multiple services, such as in payment processing systems. Here’s a breakdown of the Saga design pattern explained in the context of a payment system.
Scenario: Payment Processing System
Consider a simplified payment processing system with the following services:
Order Service: Manages customer orders.
Payment Service: Processes payments.
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Inventory Service: Manages product inventory.
Shipping Service: Handles the shipping of orders.
Key Concepts of the Saga Pattern
Types of Sagas
Example: Order Processing Saga
Let's implement a saga using the orchestration approach for an order processing system. Steps in the Saga
Compensating Transactions
Implementation Steps:
Orchestrator: A central service that manages the saga.
Services: Each service (Order, Inventory, Payment, Shipping) performs its part of the transaction and reports back to the orchestrator. Step-by-Step Example Order Service - Create Order
@RestController
public class OrderService {
@Autowired
private SagaOrchestrator sagaOrchestrator;
@PostMapping("/orders")
public ResponseEntity<Order> createOrder(@RequestBody OrderRequest orderRequest) {
Order order = new Order();
order.setStatus("PENDING");
// Save order to database
// ...
// Start the saga
sagaOrchestrator.createOrderSaga(order);
return ResponseEntity.ok(order);
}
}
Saga Orchestrator
@Service
public class SagaOrchestrator {
@Autowired
private InventoryService inventoryService;
@Autowired
private PaymentService paymentService;
@Autowired
private ShippingService shippingService;
public void createOrderSaga(Order order) {
try {
inventoryService.reserveInventory(order);
paymentService.processPayment(order);
shippingService.shipOrder(order);
completeOrder(order);
} catch (Exception e) {
compensate(order);
}
}
private void completeOrder(Order order) {
order.setStatus("COMPLETED");
// Update order status in database
// ...
}
private void compensate(Order order) {
// Rollback steps in reverse order
shippingService.cancelShipment(order);
paymentService.refundPayment(order);
inventoryService.releaseInventory(order);
cancelOrder(order);
}
private void cancelOrder(Order order) {
order.setStatus("CANCELED");
// Update order status in database
// ...
}
}
Inventory Service
@Service
public class InventoryService {
public void reserveInventory(Order order) throws Exception {
// Reserve items in inventory
// ...
if (/* failure condition */) {
throw new Exception("Inventory reservation failed");
}
}
public void releaseInventory(Order order) {
// Release reserved items
// ...
}
}
Payment Service
@Service
public class PaymentService {
public void processPayment(Order order) throws Exception {
// Process payment
// ...
if (/* failure condition */) {
throw new Exception("Payment processing failed");
}
}
public void refundPayment(Order order) {
// Refund payment
// ...
}
}
Shipping Service
@Service
public class ShippingService {
public void shipOrder(Order order) throws Exception {
// Ship order
// ...
if (/* failure condition */) {
throw new Exception("Shipping failed");
}
}
public void cancelShipment(Order order) {
// Cancel shipment
// ...
}
}
Benefits of the Saga Pattern Resilience: Each step of the saga can be retried or compensated, which makes the system more resilient to failures.
Scalability: Each service can scale independently.
Consistency: Ensures eventual consistency across distributed services.
Conclusion: The Saga pattern is essential for maintaining data consistency in a microservices architecture, especially for complex, long-running transactions like order processing in a payment system. By implementing sagas with either orchestration or choreography, you can manage distributed transactions effectively, ensuring resilience, scalability, and consistency.
System Analyst | Solution Architect | Integration Expert | Java Developer
10moVery informative