Microservices Communication Patterns (Saga, Circuit Breaker) · レッスン

Orchestration Sagaの解説

専用サービスが分散トランザクションの各ステップを調整するOrchestrationアプローチについて学習します。

レッスン 3/411 ステップ

「Orchestration Sagaの解説」はCoddyKit上の無料Microservices Communication Patterns (Saga, Circuit Breaker)レッスンです。これはレッスン3/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはMicroservices Communication Patterns (Saga, Circuit Breaker)学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Microservices Communication Patterns (Saga, Circuit Breaker)コースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Introducing Orchestration Sagas

Welcome to the Orchestration Saga! In a distributed system, sometimes a business transaction needs to involve multiple services.

An Orchestration Saga is a pattern where a central service, called an orchestrator, takes charge of guiding the entire transaction.

The Role of the Orchestrator

Think of the orchestrator as a project manager for your distributed transaction. It knows all the steps and coordinates them.

It sends commands to participant services.
It waits for responses (events) from those services.
It decides the next step based on the responses.

How it Works: A Simple Flow

Unlike a Choreography Saga where services react to events from each other, here the orchestrator is in control:

Orchestrator sends a command to Service A.
Service A performs its task and sends a completion event back to the orchestrator.
Orchestrator receives the event and sends a command to Service B.
This continues until the transaction is complete.

Example: Online Order Process

Let's use an online order as an example. An order might need to:

Create an order in the Order Service.
Reserve items in the Inventory Service.
Process payment in the Payment Service.
Initiate shipping in the Shipping Service.

An orchestrator would manage this sequence.

Orchestrator's State Management

The orchestrator must keep track of the saga's current state and context. This means it needs to store information like:

Which steps have completed?
What data was returned by previous steps?
What is the current status (e.g., PAYMENT_PENDING, INVENTORY_RESERVED)?

This state is crucial for deciding the next action or handling failures.

Commands & Events

The orchestrator communicates using two main types of messages:

Commands: Sent from the orchestrator to a service, telling it what to do (e.g., ReserveInventory).
Events: Sent from a service back to the orchestrator, reporting the outcome (e.g., InventoryReserved, PaymentFailed).

This clear distinction helps maintain control.

Handling Failures & Compensation

What if a step fails? The orchestrator is responsible for compensation.

If the Payment Service fails, the orchestrator detects the PaymentFailed event. It then knows to send compensation commands to previous services, such as ReleaseInventory to the Inventory Service and CancelOrder to the Order Service.

Orchestrator Flow Demo

Let's look at a simplified Java example. This isn't a full microservice, but it shows how an orchestrator's logic might flow, reacting to simulated service outcomes.

Notice how it tracks sagaState and triggers compensation if payment fails.

public class OrderSagaOrchestrator {

  public static void main(String[] args) {
    System.out.println("Saga Orchestrator Started: Order 123");
    String sagaState = "ORDER_INITIATED";

    System.out.println("Orchestrator: Sending 'CREATE_ORDER' command.");
    // Simulate Order Service success
    sagaState = "ORDER_CREATED";
    System.out.println("Orchestrator: Received 'ORDER_CREATED' event.");

    if (sagaState.equals("ORDER_CREATED")) {
      System.out.println("Orchestrator: Sending 'RESERVE_INVENTORY' command.");
      // Simulate Inventory Service success
      sagaState = "INVENTORY_RESERVED";
      System.out.println("Orchestrator: Received 'INVENTORY_RESERVED' event.");
    }

    if (sagaState.equals("INVENTORY_RESERVED")) {
      System.out.println("Orchestrator: Sending 'PROCESS_PAYMENT' command.");
      // Simulate Payment Service *failure*
      System.out.println("Orchestrator: Received 'PAYMENT_FAILED' event.");
      sagaState = "PAYMENT_FAILED";
    }

    if (sagaState.equals("PAYMENT_FAILED")) {
      System.out.println("Orchestrator: Initiating compensation!");
      System.out.println("Orchestrator: Sending 'CANCEL_ORDER' command.");
      System.out.println("Orchestrator: Sending 'RELEASE_INVENTORY' command.");
      sagaState = "SAGA_COMPENSATED";
      System.out.println("Orchestrator: Saga completed with compensation.");
    } else {
      System.out.println("Orchestrator: Sending 'CONFIRM_ORDER' command.");
      System.out.println("Orchestrator: Sending 'SHIP_ORDER' command.");
      sagaState = "SAGA_COMPLETED_SUCCESSFULLY";
      System.out.println("Orchestrator: Saga completed successfully.");
    }
  }
}

Advantages of Orchestration

Orchestration Sagas offer clear benefits:

Centralized Control: Easier to understand the overall flow.
Simplified Participant Services: Services don't need to know about the entire saga; they just follow orchestrator commands.
Easier Debugging: The orchestrator's state makes it simpler to trace issues.
Explicit Compensation: Compensation logic is clearly defined within the orchestrator.

Check Your Understanding

Which of the following statements accurately describe key characteristics of an Orchestration Saga?

対話的なレッスンで答える

Recap: Orchestration Saga

You've learned about the Orchestration Saga pattern!

It uses a central orchestrator service to manage a distributed transaction.
The orchestrator sends commands to services and receives events as responses.
It maintains the saga's state to know where it is in the transaction.
It explicitly handles compensation by issuing rollback commands if a step fails.

This pattern provides clear control and simplifies participant services.

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よくある質問

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はい。「Orchestration Sagaの解説」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Microservices Communication Patterns (Saga, Circuit Breaker)コースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Microservices Communication Patterns (Saga, Circuit Breaker)コースには全4レッスンが含まれています。

「Orchestration Sagaの解説」で何を学びますか？

専用サービスが分散トランザクションの各ステップを調整するOrchestrationアプローチについて学習します。ブラウザで直接実行するハンズオンコードでMicroservices Communication Patterns (Saga, Circuit Breaker)を演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

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