Incident Dossier

Circuit Half-Open Floods Requests

During a partial outage the team enabled a circuit breaker to protect a struggling downstream. After the open window elapsed, a queue of backed-up requests suddenly arrived and the downstream's metrics spiked again. The breaker had entered half-open but was letting through the full backlog instead of a single probe.

Initial failing signalHALF_OPEN admits every concurrent requestExpected behavior: exactly one probe is admitted while in HALF_OPEN · actual behavior: all concurrent requests run the operation

Progress

1Reproduce the bugRun checks

2Edit the fixOpen

3Pass checksOpen

4Submit fixOpen

Reproduction Steps

Run npm test.
Inspect the HALF_OPEN branch of breaker.run and ask what stops a second concurrent request from also running the operation.
Notice there is no gate for already-in-flight probes.
Add a probeInFlight flag and reject additional requests while it is true.

Focus Mode

Start

src/circuit.js

Likely area

src/circuit.js

Challenge Coach

Hints reveal broad direction first, then narrow toward the suspect path without showing hidden tests or exact solution code.

TopicReliability

DifficultyMedium

Est. time22 min

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Evidence Map

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workspace

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