feat(app/inbound): request body frame size metrics #4180

cratelyn · 2025-09-22T17:07:25Z

this commit introduces an additional layer of telemetry to the inbound
proxy's http router.

either http and grpc metrics are used, depending upon the policy that
authorized a given request.

this is based upon #4174, which refactored the
request body telemetry middleware to be metrics agnostic.

this change is based upon a collection of small prerequisite changes:

related previous work:

Signed-off-by: katelyn martin [email protected]

linkerd/app/inbound/src/http/router/metrics.rs

) #4119 introduced a `Permitted<T>` structure, to provide a more formal notion of a `(HttpRoutePermit, T)` tuple. during review of #4180, we had a discussion about how the inbound proxy's http router had metrics layers which were tightly coupled to the notion of a `Permitted<T>`: > This isn't a hard blocker--but this is unfortunate that we're coupling > this impl to the Permitted target type -- target types are usually an > _internal implementation detail_ and not a public api that is depended > on elsewhere. > > ... > > and then have our Permitted impl `Param<MetricsVariant> for Permitted<T>`. > > then this module remains decoupled from the concrete target types. > > That is, the metrics module is decoupled from _where it's called_--as > long as the caller provides a target that can give us what we need to > build our extractors, we're good to go. this branch performs a series of changes to decouple our metric layers' extractors from `Permitted<T>`. importantly, this has the effect of leaving the inbound metrics layers' extractors agnostic to their target: they now provide implementations like `svc::ExtractParam<BodyDataMetrics, T>` rather than `svc::ExtractParam<BodyDataMetrics, Permitted<T>>`. see #4180. --- * refactor(app/inbound): `Permitted<T>` is a struct this restructures `Permitted<T>` so that it is no longer an enum. we instead define a "dumb" enum that represents the grpc/http dichotomy, and return to a model in which `Permitted<T>` is a `struct`. Signed-off-by: katelyn martin <[email protected]> * refactor(app/inbound): `Permitted<T>` is not `T: Param<P>` in order to carve out space to allow us to define other `Param<P>` implementations for `Permitted<T>`, we remove this blanket deference to the inner `T` target. Signed-off-by: katelyn martin <[email protected]> * refactor(app/inbound): `Permitted<T>` exposes `Param<P>` impls we cannot expose `T` or any of its own parameters, but we can expose the permit, its variant, and its labels. Signed-off-by: katelyn martin <[email protected]> * refactor(app/inbound): `family` lookups accept `PermitVariant` these now accept specifically the variant, rather than the permitted target. Signed-off-by: katelyn martin <[email protected]> * refactor(app/inbound): `ExtractRecordBodyDataMetrics` is `T`-agnostic this type now can extract metrics from arbitrary targets. Signed-off-by: katelyn martin <[email protected]> * refactor(app/inbound): `ExtractRequestCount` is `T`-agnostic this type now can extract metrics from arbitrary targets. Signed-off-by: katelyn martin <[email protected]> * refactor(app/inbound): `LogicalPerRequest::from` is `T`-agnostic Signed-off-by: katelyn martin <[email protected]> --------- Signed-off-by: katelyn martin <[email protected]>

this structure representing the frame size metrics is shared by the request and response instrumentation. the `body_data::request` and `body_data::response` submodules reëxport this, because the outbound proxy which uses these middleware separately in route-level and backend-level metrics layers. the inbound proxy, however, uses them each in the same place (see #4180), which is ergonomically odd. this commit introduces a top-level `pub use`, exposing this metrics structure from `body_data`, for consumers that instrument request and response bodies in one place. Signed-off-by: katelyn martin <[email protected]>

see #4180. we will shortly introduce an additional layer of body frame size instrumentation. in order to avoid ambiguity in our extractor's names, we rename this type to `ExtractResponseBodyDataMetrics`, to indicate that it extracts _response_ body metrics. Signed-off-by: katelyn martin <[email protected]>

this structure representing the frame size metrics is shared by the request and response instrumentation. the `body_data::request` and `body_data::response` submodules reëxport this, because the outbound proxy which uses these middleware separately in route-level and backend-level metrics layers. the inbound proxy, however, uses them each in the same place (see #4180), which is ergonomically odd. this commit introduces a top-level `pub use`, exposing this metrics structure from `body_data`, for consumers that instrument request and response bodies in one place. Signed-off-by: katelyn martin <[email protected]>

see #4180. we will shortly introduce an additional layer of body frame size instrumentation. in order to avoid ambiguity in our extractor's names, we rename this type to `ExtractResponseBodyDataMetrics`, to indicate that it extracts _response_ body metrics. Signed-off-by: katelyn martin <[email protected]>

this structure representing the frame size metrics is shared by the request and response instrumentation. the `body_data::request` and `body_data::response` submodules reëxport this, because the outbound proxy which uses these middleware separately in route-level and backend-level metrics layers. the inbound proxy, however, uses them each in the same place (see #4180), which is ergonomically odd. this commit introduces a top-level `pub use`, exposing this metrics structure from `body_data`, for consumers that instrument request and response bodies in one place. Signed-off-by: katelyn martin <[email protected]>

see #4180. to make way for the use of request body metrics middleware, we use further qualified paths to `body_data::response::NewRecordBodyData`. to be consistent across the board, we apply this change to the request counting middleware as well. NB: this is based upon #4186. Signed-off-by: katelyn martin <[email protected]>

our metrics layer is generic across an `N`-typed service factory. this commit introduces types aliases that apply `X`-typed extractor parameters to the `linkerd-http-prom` middleware, which are unaware of a concrete metrics extractor. we use this to reduce the complexity of the `layer()` function's type signature. see #4180. NB: based upon #4188, and #4186. Signed-off-by: katelyn martin <[email protected]>