Designing a Circuit-Breaker System

1. What Is Circuit Breaking?

• A caller invokes a callee. When the number of errors reaches a threshold, the caller stops invoking the callee; when the callee recovers, calls resume.
• A Fail-Fast strategy in fault tolerance.

2. How to Implement Circuit Breaking

2.1. Circuit-Breaker Pattern

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• Use a proxy, the circuit-breaker object, to take over a service caller’s remote requests one-to-one: one remote service corresponds to one circuit-breaker object.
• Service A calls service B. A counts errors. When (errors + timeouts) / total requests reaches a threshold, the circuit breaker trips and A stops calling B.
• Every once in a while, let a few requests through to probe B. If B has recovered, resume calls.

3. Circuit-Breaker Component

Designing a Fault-Tolerance Component.md

4. Circuit Breaking vs Rate Limiting

• Service A calls service B.
• Circuit breaking protects A itself, while rate limiting protects service B.