Metrics¶

The imbi.common.metrics module serves the Prometheus metrics of a process at /metrics. imbi-api, imbi-gateway and imbi-scheduler add the route.

Add the route¶

Call add_route() on the root FastAPI app, not on a router with an API prefix. The route is not in the OpenAPI schema.

import fastapi

from imbi.common import metrics

app = fastapi.FastAPI()
metrics.add_route(app)

The route has no authentication. Do not expose it on a public route. The in-cluster Prometheus scrapes it by pod IP.

Registry¶

The route returns the default prometheus_client registry. Define metrics with prometheus_client at module level and they show on the route. For example, the Iggy client defines its publish counters this way.

The services run one uvicorn worker per process, so the default registry holds every metric of the process. The module does not use the multiprocess mode of prometheus_client. If a service runs more than one worker (WEB_CONCURRENCY), each scrape shows the metrics of one worker only.

API Reference¶

add_route(app: FastAPI) -> None

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def add_route(app: fastapi.FastAPI) -> None:
    """Add the ``/metrics`` route to `app`, outside the OpenAPI schema."""
    app.add_route(PATH, endpoint, include_in_schema=False)

endpoint(_request: Request) -> fastapi.Response

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async def endpoint(_request: fastapi.Request) -> fastapi.Response:
    """Return the default registry in the Prometheus text format."""
    return fastapi.Response(
        prometheus_client.generate_latest(),
        media_type=prometheus_client.CONTENT_TYPE_LATEST,
    )

PATH = '/metrics'