Choreography Saga

We will go through the process of implementing the 12st Mall using Axon, a specialized framework supporting Event Sourcing, Domain-Driven Development, and CQRS.

Specifically, we'll learn about framework-level code that orchestrates commands based on domain events.

EventStorming Model Preparation

Open the model in a new tab using the link : Model Link
If the model doesn't load, click on the avatar icon (person shape) in the upper right, log in with your Github account, and then reload.
Verify that the stickers appear in the right palette area.
Click on the Fork icon in the top menu to clone the model.

Orchestration Saga Scenario

An OrderPlaced event is generated in response to an order command.
The Order Saga process is triggered by the OrderPlaced event.
The Saga Process invokes the start delivery command and generates a DeliveryStarted event.
Subsequently, a stock deduction command is invoked, leading to the creation of a StockDecreased event.
The Saga Process concludes with the procedure to update the final order status.
If an error occurs during any command invocation, Compensation Logic is executed for each.

Saga Modeling

Click on the Fork menu at the top.
Orchestrate the cloned model as follows:

Process Orchestration

The rules for orchestrating the Saga model are as follows:

Connect stickers with lines: 'From Sticker' > 'To Sticker'

Click on mapping relations to label them. Labels indicate the execution order.

Among the labels, processes marked with '가' are Compensation Trx processes.

OrderPlaced > Order Saga, (1.start)

Order Saga > start delivery, (2)

DeliveryStarted > Order Saga, (3)

Order Saga > decrease stock, (4)

StockDecreased > Order Saga, (5)

Order Saga > update status, (6)

OrderCompleted > Order Saga, (7.end)

Order Saga > order cancel, (2')

Order Saga > cancel delivery, (4')

The orchestrated Saga model looks like this:

Code Generation and Push to My Git Repository

Click on Git icon in Code Preview to push the generated code to your repository.

GitPod 환경에서 로딩한다.

Verify Axon Server

infra > docker-compose.yml

Axon Server uses port 8024 for the dashboard and 8124 for gRPC messaging.
A Token Store (MySQL) for managing offset tokens is created during Lab execution.

Orchestration Saga Code Completion

Product Service

Complete the business logic in the product domain code.

Add code to throw a domain error if there is insufficient stock in the @DecreaseStockCommand.

# ProductAggregate - @DecreaseStockCommand throw an exception for insufficient stock
	if(this.getStock() < command.getStock()) throw new IllegalStateException("Out of Stock. !");  // Add this line

Add the following code to ProductAggregate.java in the product service:

# @EventSourcingHandler :: StockIncreasedEvent : 
    setStock(getStock() + event.getStock());  // Add this line

#  @EventSourcingHandler :: StockDecreasedEvent : 
    setStock(getStock() - event.getStock());  // Add this line

Order Service

Complete the business logic in the order domain code.

Add the following code to OrderAggregate.java in the order service:

# @EventSourcingHandler :: OrderPlacedEvent :
     setStatus("OrderPlaced"); 			// Add this line
# @EventSourcingHandler :: OrderCompletedEvent : 
     setStatus("OrderCompleted"); 		// Add this line
# @EventSourcingHandler :: OrderCancelledEvent :      
      setStatus("OrderCancelled");		// Add this line

Delivery Service

Complete the business logic in the delivery domain code.

Add the following code to DeliveryAggregate.java in the delivery service:

# @EventSourcingHandler :: DeliveryStartedEvent :
      setStatus("DeliveryStarted"); 		// Add this line
# @EventSourcingHandler :: DeliveryCancelledEvent : 
      setStatus("DeliveryCancelled"); 		// Add this line

OrderSaga

Complete the OrderSaga code to perform the order orchestration.

1. Saga Start

Set correlation key from the OrderPlaced event: Line 24

@SagaEventHandler(associationProperty = "orderId")

2. Generate and Invoke Start Delivery Command: Line 27

command.setOrderId(event.getOrderId());
command.setProductId(event.getProductId());
command.setQty(event.getQty());
command.setUserId(event.getUserId());

# If delivery fails, handle compensation: OrderCancelCommand
orderCancelCommand.setOrderId(event.getOrderId());  	// Add this line

3. Set Correlation Key from DeliveryStartedEvent

@SagaEventHandler(associationProperty = "orderId")

4. Generate and Invoke Decrease Stock Command

command.setProductId(event.getProductId());
command.setStock(event.getQty());	
command.setOrderId(event.getOrderId());

# If stock deduction fails, handle compensation: CancelDeliveryCommand
cancelDeliveryCommand.setDeliveryId(event.getDeliveryId());	// Add this line

5. Set Correlation Key from StockDecreasedEvent

@SagaEventHandler(associationProperty = "orderId")

6. Generate and Invoke Order Completed Command

command.setOrderId(event.getOrderId());

7. Saga End

Set Correlation Key from OrderCompletedEvent

@SagaEventHandler(associationProperty = "orderId")

End Saga Process

12st Mall Test

Test the Axon Saga-based mall using Rest API.
First, build the Common API:

cd common-api
mvn clean install

Run each microservice:

# new terminal
cd order
mvn clean spring-boot:run

# new terminal
cd product
mvn clean spring-boot:run

# new terminal
cd delivery
mvn clean spring-boot:run

# new terminal
http POST :8082/products productName=TV stock=100

Copy the product ID.
Create an order for purchasing 10 TVs using the copied product ID:

http POST :8081/orders productId=[상품 Id] productName=TV qty=10 userId=1001

Copy the order ID.

12st Mall Saga Compensation Verification

Create an Order

Create an order to purchase 100 TVs using the product ID, and copy the order number:

http POST :8081/orders productId=[상품 Id] productName=TV qty=100 userId=1001

The product service returns an error since the quantity exceeds the available stock.

Check the final status and event history of the created order using the order number:

http GET :8081/orders/[Order Number]
http GET :8081/orders/[Order Number]/events

Check the delivery status in the delivery service:

http GET :8083/deliveries

[Extension Mission] - Order Service Debugging

Stop the order service.
Add breakpoints for each SagaEventHandler in OrderSaga.
Run the order service in debug mode.
Create a new order and observe the orchestration flow by checking the Debug Points.
Test by placing an order with a quantity greater than the available stock.

On this page