Circuit Breaker

You might say

The payment dependency keeps timing out. Stop making every request wait, fail fast or degrade, and probe it again after a pause.

A circuit breaker cuts off a repeatedly failing dependency, fails fast or degrades, and probes recovery laterWhen a checkout page calls a payment dependency that keeps timing out, continuing to wait and retry can exhaust the caller's threads and request queue. A breaker moves through Closed, Open, and Half-Open: normal calls pass while Closed; repeated failures open it for fast failure or fallback; a later limited probe tests recovery, returning to Closed on success or Open on failure. It is different from one timeout or retry and cannot repair the dependency.

How a breaker stops a dependency failure from spreading

Order service calling paymentsNormal forwarding

order requestpasses breaker

payment service200 OK

breakerClosed

EvidenceSuccess and latency remain within threshold

Requests pass while the dependency is healthy.

Three states decide whether calls continue

Problem and key mechanism: Repeated dependency timeouts or failures accumulate waiting and resource use at the caller; after crossing the threshold, the circuit breaker moves from Closed to Open for fast failure or fallback, then allows only a small probe in Half-Open after a pause.

Feedback decides recovery: A successful probe returns to Closed; a failed probe opens the circuit again. The caller is protected, but the breaker does not repair or guarantee the dependency.

A second scenario: weather lookup: A trip page depends on an external weather API. After repeated failures, it can temporarily return a cached forecast with its update time and stop calling the dependency, then use a few probes before restoring normal lookup.

You can say this to an AI Agent

Add a circuit breaker around the payment dependency: stay Closed normally, enter Open after repeated failures with fast failure or a clear fallback, then move to Half-Open for a small recovery probe. Return to Closed only after success. Simulate timeouts and recovery, and verify the state, user feedback, and probe are observable.

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The payment dependency keeps failing while new checkout requests wait. What should the circuit breaker do next?

A. Keep increasing retries so every request waits for payment successB. Return to Closed immediately and send every new request to the failing dependencyC. Enter Open, fail fast or degrade, then probe later in Half-Open