Circuit Half-Open Floods Requests Debugging Lab

Circuit Half-Open Floods RequestsReliabilityMediumPreparing workspaceAutosaved

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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 exactly one probe is admitted while in HALF_OPEN · received 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

Progressive hints

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

TopicReliability

DifficultyMedium

Est. time22 min

Workspacecreating

Explorer

Preparing workspace files…

Evidence Map

Failing signal loaded from challenge API
Workspace files loaded from workspace API
Results rendered only after API run/submit

Autosaved

workspace

Outputread-onlyready$ workspace boot

Workspace booting...