Circuit Breaker pattern — resilient microservices with Hystrix

Service A → B → C. C fails. B waits for a timeout, exhausts the thread pool. A waits for B. Cascading failure. The Circuit Breaker breaks this chain.

Netflix Hystrix¶

public class GetUserCommand extends HystrixCommand<User> {
    @Override
    protected User run() {
        return client.getUser(userId);
    }
    @Override
    protected User getFallback() {
        return User.anonymous();
    }
}

Three states: Closed (normal), Open (blocked, fallback), Half-Open (probe call). Thread pool isolation — bulkhead pattern. Hystrix Dashboard for real-time visualisation.

Fallback strategies¶

• Static/cached value
• Degraded response
• Alternative service
• Fail fast (better than a timeout)

Circuit Breaker is essential equipment¶

In a distributed system, things fail. CB prevents cascading collapse.