イベントバスとメッセージブローカー
メッセージブローカーとイベントバスを利用し、Choreography Sagaにおける信頼性の高い非同期通信を実現します。
「イベントバスとメッセージブローカー」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2/4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。
Reliable Choreography Sagas
In a choreography saga, services communicate by exchanging events. For this to work reliably in a distributed system, we need robust communication mechanisms.
Imagine an order being created, then needing payment, and finally shipping. Each step is an event triggering the next service.
- Order Service publishes
OrderCreated - Payment Service subscribes to
OrderCreated, publishesPaymentProcessed - Shipping Service subscribes to
PaymentProcessed, publishesShipmentScheduled
What's an Event Bus?
An Event Bus is a pattern that enables different parts of an application (or different services) to communicate by sending and receiving events without knowing about each other directly.
Think of it as a central hub where events are broadcast. Any interested party can 'listen' for specific events.
It decouples services, meaning they don't need to know who will process their events, only that an event occurred.
Event Bus in Action
Consider an internal event bus within a single application:
- A user clicks a 'Save' button.
- The UI component publishes a
UserSavedevent to the event bus. - A logging module, a notification module, and a data synchronization module might all subscribe to
UserSaved.
They all react to the event without the UI knowing about them. This is simple and effective for in-process communication.
Introducing Message Brokers
While an event bus is great for in-process communication, distributed microservices need more. This is where Message Brokers come in.
A message broker is a dedicated service (like RabbitMQ, Kafka, or AWS SQS) that acts as an intermediary for messages between different applications or services.
It provides advanced features essential for reliable communication across networks.
Broker Benefits for Sagas
Message brokers offer crucial benefits for choreography sagas:
- Durability: Messages persist even if services are down, preventing data loss.
- Guaranteed Delivery: Ensures messages reach their intended consumers.
- Decoupling: Senders and receivers don't know each other, promoting service independence.
- Load Balancing: Distributes messages efficiently among multiple instances of a consuming service.
- Asynchronous: Services don't wait for responses, improving performance and responsiveness.
Bus vs. Broker: The Difference
While both facilitate event-driven communication, an Event Bus is typically a lightweight, in-memory mechanism within a single application or process.
A Message Broker is a robust, external system designed for inter-process and inter-service communication across a network. It provides features like message queues, topics, persistence, and complex routing.
You can think of a message broker as a powerful, distributed implementation of an event bus concept.
Brokers Enable Choreography
Message brokers are the backbone of choreography sagas. They allow services to:
- Publish Events: A service completes a step and publishes an event to a specific topic (a named channel on the broker).
- Subscribe to Events: Other services interested in that event subscribe to the topic and receive the event to trigger their next step.
This decentralized flow, driven by events through a broker, defines the choreography pattern.
Example: Publishing an Event
Here's a simplified example of how an OrderService might prepare and conceptually "publish" an OrderCreated event using a message broker.
The broker handles the actual sending to subscribers.
public class OrderService {
public static void main(String[] args) {
String orderId = "ORD_456";
String customer = "Alice";
String item = "Widget";
// Imagine this event goes to a message broker
String eventPayload = "{ \"type\": \"OrderCreated\", \"orderId\": \"" + orderId + "\", \"customer\": \"" + customer + "\", \"item\": \"" + item + "\" }";
System.out.println("OrderService prepares event:");
System.out.println(eventPayload);
System.out.println("This event would be sent to a 'order_events' topic on a message broker.");
}
}Example: Subscribing to an Event
Now, let's see how a PaymentService would conceptually "subscribe" to and process the OrderCreated event from the broker.
It listens on the order_events topic.
public class PaymentService {
public static void main(String[] args) {
// Imagine PaymentService receives this event from a message broker
String receivedEvent = "{ \"type\": \"OrderCreated\", \"orderId\": \"ORD_456\", \"customer\": \"Alice\", \"item\": \"Widget\" }";
System.out.println("PaymentService received event:");
System.out.println(receivedEvent);
// Parse and process the event
if (receivedEvent.contains("\"type\": \"OrderCreated\"")) {
System.out.println("Processing payment for order: ORD_456...");
System.out.println("Payment processed successfully!");
} else {
System.out.println("Unknown event type received.");
}
}
}Check Your Understanding
Message brokers are crucial for choreography sagas. Which of the following are key benefits provided by message brokers for reliable asynchronous communication?
Recap: Event Bus & Brokers
In this lesson, we explored how Event Buses and Message Brokers facilitate reliable asynchronous communication, especially for choreography sagas.
- An Event Bus is a pattern for in-process event communication.
- A Message Broker is an external, robust system that implements this pattern for distributed services, offering features like durability and guaranteed delivery.
- They enable services to publish events and subscribe to topics, forming the core of how choreography sagas progress.
Next, we'll look at how to handle compensation when things go wrong in these event-driven flows!
AI チューターと学ぶ Microservices Communication Patterns (Saga, Circuit Breaker) — 無料
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- コース
- 12
- レッスン
- 48
よくある質問
「イベントバスとメッセージブローカー」レッスンは無料ですか？
はい。「イベントバスとメッセージブローカー」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。
「イベントバスとメッセージブローカー」で何を学びますか？
メッセージブローカーとイベントバスを利用し、Choreography Sagaにおける信頼性の高い非同期通信を実現します。 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。
Microservices Communication Patterns (Saga, Circuit Breaker)を始めるのに経験は必要ですか？
事前経験は必要ありません。CoddyKitのMicroservices Communication Patterns (Saga, Circuit Breaker)は初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。 これはレッスン2/4です。
「イベントバスとメッセージブローカー」レッスンにはどのくらい時間がかかりますか？
ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。
このMicroservices Communication Patterns (Saga, Circuit Breaker)レッスンでコードを書いて実行できますか？
はい。すべてのMicroservices Communication Patterns (Saga, Circuit Breaker)レッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。
このコースのすべてのレッスン
- イベント駆動型Sagaの設計
- イベントバスとメッセージブローカー
- イベントによる補償処理
- 冪等なイベントコンシューマーの構築