サービス呼び出しへの統合
サーキットブレーカーをマイクロサービスに統合し、外部サービスの呼び出しをラップして障害から保護します。
「サービス呼び出しへの統合」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。
Wrap Up Your Calls!
Welcome to the final lesson on implementing Circuit Breakers! Today, we'll get hands-on and learn how to integrate a circuit breaker directly into your microservice's external calls.
Protecting these calls is crucial for building resilient systems that can gracefully handle failures and maintain responsiveness, even when dependencies are struggling.
Direct Service Calls
Imagine your service needs data from another microservice. A common way to do this is a direct method call or HTTP request. But what happens if that external service is slow or down?
Let's look at a basic setup without any protection.
import java.util.concurrent.ThreadLocalRandom;
class ExternalService {
public String getData() throws Exception {
System.out.println("ExternalService: Attempting to get data...");
// Simulate success for now
return "Data from external service";
}
}
public class Main {
public static void main(String[] args) {
ExternalService service = new ExternalService();
try {
String result = service.getData();
System.out.println("Result: " + result);
} catch (Exception e) {
System.err.println("Error: " + e.getMessage());
}
}
}Simulating Service Failure
In the real world, external services aren't always perfect. They can fail due to network issues, overload, or bugs. Let's update our ExternalService to simulate these failures randomly.
Run the code a few times. You'll see how a single failure can break our Main application.
import java.util.concurrent.ThreadLocalRandom;
class ExternalService {
private int callCount = 0;
public String getData() throws Exception {
callCount++;
System.out.println("ExternalService: Call #" + callCount);
// Simulate failure 50% of the time
if (ThreadLocalRandom.current().nextDouble() < 0.5) {
throw new RuntimeException("Simulated External Service Failure!");
}
return "Data from external service (call #" + callCount + ")";
}
}
public class Main {
public static void main(String[] args) {
ExternalService service = new ExternalService();
for (int i = 0; i < 3; i++) {
System.out.println("--- Attempt " + (i + 1) + " ---");
try {
String result = service.getData();
System.out.println("Result: " + result);
} catch (Exception e) {
System.err.println("Error: " + e.getMessage());
}
System.out.println();
try { Thread.sleep(200); } catch (InterruptedException e) { Thread.currentThread().interrupt(); }
}
}
}The Circuit Breaker Wrapper
This is where the Circuit Breaker comes in! Instead of calling the external service directly, we 'wrap' the call with our circuit breaker.
The circuit breaker then manages the call, decides if it should even be attempted (if the circuit is open), and handles failures. Here's a very simplified version of how such a wrapper might look:
import java.util.concurrent.Callable;
class MyCircuitBreaker {
// In a real CB, this would manage state (open, closed, half-open)
// and apply thresholds. For this lesson, we focus on the integration.
public <T> T execute(Callable<T> primaryCall) throws Exception {
try {
System.out.println("CB: Executing primary call...");
return primaryCall.call(); // Attempt the actual service call
} catch (Exception e) {
// A real CB would update its state here (e.g., trip the circuit)
System.err.println("CB: Primary call failed: " + e.getMessage());
throw e; // Re-throw for now, we'll add fallback later
}
}
}Basic CB Integration
Now let's use our basic MyCircuitBreaker to wrap the calls to our unreliable ExternalService. Notice how the Main method now uses the circuit breaker's execute method.
Run this code. While it still shows errors, the circuit breaker is now involved in mediating the calls.
import java.util.concurrent.Callable;
import java.util.concurrent.ThreadLocalRandom;
// --- MyCircuitBreaker (Simplified) ---
class MyCircuitBreaker {
public <T> T execute(Callable<T> primaryCall) throws Exception {
try {
System.out.println("CB: Executing primary call...");
return primaryCall.call();
} catch (Exception e) {
System.err.println("CB: Primary call failed: " + e.getMessage());
throw e;
}
}
}
// --- ExternalService (from previous scene) ---
class ExternalService {
private int callCount = 0;
public String getData() throws Exception {
callCount++;
System.out.println("ExternalService: Call #" + callCount);
if (ThreadLocalRandom.current().nextDouble() < 0.5) {
throw new RuntimeException("Simulated External Service Failure!");
}
return "Data from external service (call #" + callCount + ")";
}
}
// --- Main Application ---
public class Main {
public static void main(String[] args) {
ExternalService service = new ExternalService();
MyCircuitBreaker circuitBreaker = new MyCircuitBreaker();
for (int i = 0; i < 3; i++) {
System.out.println("--- Attempt " + (i + 1) + " ---");
try {
String result = circuitBreaker.execute(
() -> service.getData() // The operation to protect
);
System.out.println("Result: " + result);
} catch (Exception e) {
System.err.println("Main: Caught error after CB: " + e.getMessage());
}
System.out.println();
try { Thread.sleep(200); } catch (InterruptedException e) { Thread.currentThread().interrupt(); }
}
}
}Graceful Failure: Fallbacks
Catching errors is good, but what if we could provide a default or alternative response when the primary service call fails or the circuit is open? This is where fallbacks come in.
- A fallback is a predefined action or value that gets returned when the main operation cannot complete successfully.
- It helps maintain a good user experience by preventing total outages and providing partial functionality.
- Think of it as a 'plan B' for your service calls.
Implementing Fallback Logic
We'll enhance our MyCircuitBreaker to accept a second Callable: the fallback operation. If the primaryCall fails, the fallbackCall will be executed instead.
This makes our circuit breaker much more useful for handling failures gracefully.
import java.util.concurrent.Callable;
class MyCircuitBreaker {
public <T> T execute(Callable<T> primaryCall, Callable<T> fallbackCall) {
try {
System.out.println("CB: Executing primary call...");
return primaryCall.call();
} catch (Exception e) {
System.err.println("CB: Primary call failed. Invoking fallback: " + e.getMessage());
try {
// If primary fails, invoke the fallback
return fallbackCall.call();
} catch (Exception fallbackE) {
System.err.println("CB: Fallback call also failed: " + fallbackE.getMessage());
return null; // Or throw a specific exception if fallback is critical
}
}
}
}Putting It All Together
Now, let's see the full picture. We'll use our updated MyCircuitBreaker with both the primary service call and a simple fallback message.
Run this code multiple times. When the ExternalService fails, you'll now get the fallback message instead of an error in your Main application!
import java.util.concurrent.Callable;
import java.util.concurrent.ThreadLocalRandom;
// --- MyCircuitBreaker (with Fallback) ---
class MyCircuitBreaker {
public <T> T execute(Callable<T> primaryCall, Callable<T> fallbackCall) {
try {
System.out.println("CB: Executing primary call...");
return primaryCall.call();
} catch (Exception e) {
System.err.println("CB: Primary call failed. Invoking fallback: " + e.getMessage());
try {
return fallbackCall.call();
} catch (Exception fallbackE) {
System.err.println("CB: Fallback call also failed: " + fallbackE.getMessage());
return null;
}
}
}
}
// --- ExternalService (with failures) ---
class ExternalService {
private int callCount = 0;
public String getData() throws Exception {
callCount++;
System.out.println("ExternalService: Call #" + callCount);
if (ThreadLocalRandom.current().nextDouble() < 0.5) {
throw new RuntimeException("Simulated External Service Failure!");
}
return "Data from external service (call #" + callCount + ")";
}
}
// --- Main Application ---
public class Main {
public static void main(String[] args) {
ExternalService service = new ExternalService();
MyCircuitBreaker circuitBreaker = new MyCircuitBreaker();
System.out.println("Attempting to fetch data with Circuit Breaker and Fallback:");
for (int i = 0; i < 5; i++) {
System.out.println("--- Attempt " + (i + 1) + " ---");
String result = circuitBreaker.execute(
() -> service.getData(), // Primary operation
() -> "Fallback: Service is currently unavailable." // Fallback operation
);
System.out.println("Result: " + result);
System.out.println();
try { Thread.sleep(200); } catch (InterruptedException e) { Thread.currentThread().interrupt(); }
}
}
}Strategic Integration Points
Where exactly should you place circuit breakers in your architecture?
- Service Clients: Wrap all calls made from your service to other external services. This is the most common place.
- API Gateways: If you use an an API Gateway, it's an excellent place to implement circuit breakers for calls to downstream microservices, protecting your frontend from direct service failures.
- Dedicated Proxy Layers: For very complex systems, a dedicated proxy or sidecar pattern can manage circuit breakers transparently for all outbound calls.
Integrating Circuit Breakers
You've learned how to wrap external service calls with a Circuit Breaker. Let's check your understanding.
Lesson Summary
Great job! In this lesson, you've learned the practical steps of integrating a circuit breaker into your microservice calls. We covered:
- The risks of unprotected external service calls.
- How to 'wrap' a service call using a circuit breaker's
executemethod. - The importance and implementation of fallback operations for graceful degradation.
- Common strategic points in your architecture for integrating circuit breakers.
By applying these techniques, you can significantly enhance the resilience and stability of your distributed systems. Keep practicing!
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- コース
- 12
- レッスン
- 48
よくある質問
「サービス呼び出しへの統合」レッスンは無料ですか？
はい。「サービス呼び出しへの統合」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。
「サービス呼び出しへの統合」で何を学びますか？
サーキットブレーカーをマイクロサービスに統合し、外部サービスの呼び出しをラップして障害から保護します。 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3/4です。
「サービス呼び出しへの統合」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。