Commits on Oct 14, 2024

1. feat(app): Add hostname label to route metrics …

   this commit introduces an additional label to HTTP and gRPC route
   metrics, containing the DNS host of requests. requests destined for an
   ip address of some kind are not recorded with a hostname metric, as a
   way to help minimize the impact of time series cardinality.
   
   the core of this change is in this field addition:
   
   ```diff
   // /linkerd/app/outbound/src/http/logical/policy/route/metrics/labels.rs
   -pub struct Route(pub ParentRef, pub RouteRef);
   +pub struct Route {
   +    parent: ParentRef,
   +    route: RouteRef,
   +    hostname: Option<dns::Name>,
   +}
   ```
   
   see this part of the change to our `MkStreamLabel` implementation, used
   in our metrics tracking request durtion, and counting response status
   codes:
   
   ```diff
   -    fn mk_stream_labeler<B>(&self, _: &::http::Request<B>) -> Option<Self::StreamLabel> {
   +    fn mk_stream_labeler<B>(&self, req: &::http::Request<B>) -> Option<Self::StreamLabel> {
            let parent = self.params.parent_ref.clone();
            let route = self.params.route_ref.clone();
   -        Some(metrics::LabelHttpRsp::from(metrics::labels::Route::from((
   -            parent, route,
   -        ))))
   +        Some(metrics::LabelHttpRsp::from(metrics::labels::Route::new(
   +            parent,
   +            route,
   +            req.uri(),
   +        )))
        }
   ```
   
   we now inspect the request, and use the URI to label metrics related to
   this traffic by hostname.
   
   a `http_request_hostnames()` test case is added to exercise this.
   
   some todo comments are left, noting where we would ideally like to
   simplify or generalize the machinery related to `RetryLabelExtract`, the
   type that bridges the labels needed based on our `NewService<T>` target,
   and the request type later accepted by the instantiated `Service<T>`.
   
   Signed-off-by: katelyn martin <[email protected]>

   

   cratelyn committed Oct 14, 2024
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