vllm.entrypoints.serve.instrumentator.metrics

Functions:

• attach_router –

  Mount prometheus metrics to a FastAPI app.

_patch_instrumentator_route_walk()

Make prometheus-fastapi-instrumentator's route walk tolerate routes without a .path.

FastAPI >= 0.137 stores lazy _IncludedRouter objects in app.routes; these are BaseRoute subclasses with no .path attribute. The instrumentator's _get_route_name (up to 8.0.0) reads route.path unconditionally, so every request raises AttributeError in the metrics middleware and the server returns 500 (e.g. /health never goes ready). Skip path-less routes; this only affects the metric handler label, not request routing. Idempotent.

Source code in vllm/entrypoints/serve/instrumentator/metrics.py

def _patch_instrumentator_route_walk() -> None:
    """Make prometheus-fastapi-instrumentator's route walk tolerate routes
    without a ``.path``.

    FastAPI >= 0.137 stores lazy ``_IncludedRouter`` objects in ``app.routes``;
    these are ``BaseRoute`` subclasses with no ``.path`` attribute. The
    instrumentator's ``_get_route_name`` (up to 8.0.0) reads ``route.path``
    unconditionally, so every request raises ``AttributeError`` in the metrics
    middleware and the server returns 500 (e.g. ``/health`` never goes ready).
    Skip path-less routes; this only affects the metric handler label, not
    request routing. Idempotent.
    """

    def _get_route_name(scope: Scope, routes, route_name=None):
        for route in routes:
            if getattr(route, "path", None) is None:
                continue
            match, child_scope = route.matches(scope)
            if match == Match.FULL:
                route_name = route.path
                child_scope = {**scope, **child_scope}
                if isinstance(route, Mount) and route.routes:
                    child = _get_route_name(child_scope, route.routes, route_name)
                    route_name = None if child is None else route_name + child
                return route_name
            elif match == Match.PARTIAL and route_name is None:
                route_name = route.path
        return None

    _pfi_routing._get_route_name = _get_route_name

attach_router(app)

Mount prometheus metrics to a FastAPI app.

Source code in vllm/entrypoints/serve/instrumentator/metrics.py

def attach_router(app: FastAPI):
    """Mount prometheus metrics to a FastAPI app."""
    registry = get_prometheus_registry()

    # `response_class=PrometheusResponse` is needed to return an HTTP response
    # with header "Content-Type: text/plain; version=0.0.4; charset=utf-8"
    # instead of the default "application/json" which is incorrect.
    # See https://github.com/trallnag/prometheus-fastapi-instrumentator/issues/163#issue-1296092364
    Instrumentator(
        excluded_handlers=[
            "/metrics",
            "/health",
            "/load",
            "/ping",
            "/version",
            "/server_info",
        ],
        registry=registry,
    ).add().instrument(app).expose(app, response_class=PrometheusResponse)

    # Add prometheus asgi middleware to route /metrics requests
    metrics_route = Mount("/metrics", make_asgi_app(registry=registry))

    # Workaround for 307 Redirect for /metrics
    metrics_route.path_regex = re.compile("^/metrics(?P<path>.*)$")
    app.routes.append(metrics_route)