Multiproc doesn't capture all metrics

まず、issue に示されている FastAPI のマルチプロセス collector のパスとカスタム /metrics ハンドラーを再現します。counter、gauge、histogram の挙動を比較しながら、CollectorRegistry、MultiProcessCollector、および PROMETHEUS_MULTIPROC_DIR の出力を調査します。完了の条件は、histogram が存在しない理由を特定し、期待されるメトリクスがレンダリングされることを確認することです。

Hey folks,

I have a similar setup to what is described here. The only difference is that I have nginx in front talking to gunicorn over sockets, but I don't think that matters as far as I can tell.

I wasn't able to use this code:

# Using multiprocess collector for registry
def make_metrics_app():
    registry = CollectorRegistry()
    multiprocess.MultiProcessCollector(registry)
    return make_asgi_app(registry=registry)


metrics_app = make_metrics_app()
app.mount("/metrics", metrics_app)

It results in a page that gets a 307, so I implemented this:

@router.get("/metrics", response_class=PlainTextResponse, include_in_schema=False)
async def get_metrics() -> str:
    """
    Get prometheus metrics
    """
    registry = CollectorRegistry()
    multiprocess.MultiProcessCollector(registry)
    data = generate_latest(registry)
    res = Response(content=data)
    res.headers["Content-Type"] = CONTENT_TYPE_LATEST
    res.headers["Content-Length"] = str(len(data))
    return res

Apart from that my setup is pretty typical, I have some counters and a histogram:

AUTOMATIONS_TOTAL: Final = Gauge(
    name=prefix_("automations_total"),
    documentation="Number of automations run",
    labelnames=["platform", "action", "kind", "status"],
    multiprocess_mode="sum",
)

REQUEST_TIME_SECONDS: Final = Histogram(
    name=prefix_("request_time_seconds"),
    documentation="Time spent processing request",
    labelnames=["method", "url_rule", "status_code"],
)

REQUESTS_IN_PROGRESS_TOTAL: Final = Gauge(
    name=prefix_("requests_in_progress_total"),
    documentation="Number of concurrent requests",
    # See Metrics Tuning (Gauge)
    # https://github.com/prometheus/client_python#multiprocess-mode-gunicorn
    multiprocess_mode="sum",
)

My in progress counter always remains at zero, but I'm hoping that's because requests finish faster than I can see them. The histogram, however, never shows up - I see no record of it in my PROMETHEUS_MULTIPROC_DIR and it's never rendered in the output. Any ideas for what I could troubleshoot?