/metrics reports OPEN and HALF_OPEN breaker states swapped

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Business impact

gateway_circuit_breaker_state is the numeric metric an alerting rule or dashboard would graph to know when an upstream's breaker trips (its own doc comment says "0=closed, 1=open, 2=half_open"). Right now open and half_open are swapped in the lookup table that feeds this gauge -- so a dashboard built against the documented mapping shows an upstream as merely probing recovery (2, half-open) at the exact moment it is fully open and rejecting all traffic, and shows it as fully open (1) during the brief, mostly-harmless half-open probing window. Anyone paging off this metric with "alert if value == 1" would get paged for the wrong condition, or miss the real outage.

Problem

GET /admin/breakers (string-based, reading BreakerState values directly) correctly reports "open" for an open breaker. /metrics (numeric, going through set_breaker_state_metric) reports 2 for that same breaker at the same moment -- which the gauge's own help text says means half-open.

Current behavior

_BREAKER_STATE_VALUE maps "open" to 2 and "half_open" to 1 -- the two values are swapped relative to the gauge's own documented mapping (0=closed, 1=open, 2=half_open) three lines above it.

Expected behavior

The numeric value /metrics reports for a given upstream always agrees with what GET /admin/breakers reports for that same upstream, using the mapping documented in gateway_circuit_breaker_state's help text: 0=closed, 1=open, 2=half_open.

Steps to reproduce

Trip a breaker (enough consecutive failures against a route).
Compare GET /admin/breakers (says "open") against the gateway_circuit_breaker_state{upstream="..."} line in GET /metrics (reads 2, should read 1).

Why this matters

This is a two-systems-disagree-about-one-fact bug: the string-based snapshot (BreakerRegistry.snapshot()) and the numeric metric (set_breaker_state_metric) are two independent representations of the exact same underlying BreakerState, fed by two independent lookup tables that are supposed to agree and do not. Nothing in either code path would ever notice the mismatch on its own -- only comparing the two against each other (or against the documented mapping) surfaces it.

Suggested approach

Compare _BREAKER_STATE_VALUE in app/metrics.py against the numbers documented in circuit_breaker_state's own Gauge(...) help text three lines above it.

Acceptance criteria

_BREAKER_STATE_VALUE["open"] == 1 and _BREAKER_STATE_VALUE["half_open"] == 2, matching the gauge's documented mapping
For any breaker, the numeric value read via /metrics and the state string read via /admin/breakers refer to the same actual state at every transition (closed -> open -> half_open -> closed)

Verification

pytest practice_tickets/tests/test_ticket_10_metrics_breaker_state_swapped.py -v

Hints (0/2)

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$git checkout -b fix/metrics-breaker-state-swapped

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Questions

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The project

Dynamic API Gateway & Reverse Proxy

A FastAPI reverse proxy that streams every request and response without ever buffering a body in full, with hot-reloadable routing, per-route auth, Redis token-bucket rate limiting, and a per-upstream circuit breaker.

Fork on GitHub

Download

Setup

Dynamic API Gateway & Reverse Proxy

git clone <your-fork>
cd FastAPIDevTraining/gateway_proxy
cp .env.example .env   # adjust GATEWAY_ADMIN_TOKEN etc. if you like
docker compose up --build   # Redis + the gateway (uvicorn --reload) + 2 demo upstreams

The gateway is reachable at . Two demo upstreams come up alongside it — (low-latency JSON echo at , plus for the streaming-passthrough demo) and (, , for timeout and circuit-breaker demos) — and wires five example routes against them, one per feature. Verify the stack with (liveness only) and (pings Redis, which every rate-limited route depends on). Every endpoint (route CRUD, reload, persist, breaker snapshot) requires .