Answer Key: Circuit Breaker Pattern

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Exercise 1: Implement Circuit Breaker

Question: Implement a circuit breaker. What are the states?

Answer

Circuit Breaker States: - Closed: Normal operation, calls pass through - Open: Service failing, calls rejected - Half-open: Testing if service recovered

State transitions: Closed → Open (on failure), Open → Half-open (on timeout), Half-open → Closed (on success).

Answer: Three states (closed/open/half-open), transitions based on failure/success.

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Exercise 2: Configure Thresholds

Question: Configure circuit breaker thresholds. What values?

Answer

Thresholds: - Error rate: 50% errors - Latency: P95 > 1 second - Timeout: 30 seconds open state - Success threshold: 5 successes to close

Answer: 50% error threshold, P95 latency, 30s timeout, 5 successes to recover.

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Exercise 3: Handle Recovery

Question: Your circuit breaker opens. How does it recover?

Answer

Recovery Process: 1. Wait: Wait for timeout (30 seconds) 2. Test: Transition to half-open, allow test requests 3. Evaluate: Evaluate test results 4. Close: Close if successful, reopen if failed

Answer: Wait timeout → half-open → test → evaluate → close on success, reopen on failure.