feat(app): Add hostname field to HTTP route labels

linkerd/app/outbound/src/http/logical/policy/route.rs

@@ -163,6 +163,9 @@ impl<T: Clone, M, F, P> svc::Param<HttpRouteLabels> for MatchedRoute<T, M, F, P>
         HttpRouteLabels(
             self.params.parent_ref.clone(),
             self.params.route_ref.clone(),
+            // we do not know the hostname at instantiation time for the stack. this is found
+            // later when we are creating our labeler.
+            None,
         )
     }
 }
@@ -183,14 +186,14 @@ impl<T> filters::Apply for Http<T> {
 
 impl<T> metrics::MkStreamLabel for Http<T> {
     type StatusLabels = metrics::labels::HttpRouteRsp;
-    type DurationLabels = metrics::labels::HttpRoute;
+    type DurationLabels = metrics::labels::HttpRoute; // TODO(kate): do we want hostname here?
     type StreamLabel = metrics::LabelHttpRouteRsp;
 
-    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::HttpRoute::from((parent, route)),
+            metrics::labels::HttpRoute::from((parent, route, req.uri().host().map(str::to_owned))),
         ))
     }
 }

linkerd/app/outbound/src/http/logical/policy/route/metrics/labels.rs

@@ -5,7 +5,8 @@ use prometheus_client::encoding::*;
 use crate::{BackendRef, ParentRef, RouteRef};
 
 #[derive(Clone, Debug, Hash, PartialEq, Eq)]
-pub struct HttpRoute(pub ParentRef, pub RouteRef);
+pub struct HttpRoute(pub ParentRef, pub RouteRef, pub Option<Host>);
+type Host = String; // TODO(kate): use `url::Host` rather than bare strings.
 
 #[derive(Clone, Debug, Hash, PartialEq, Eq)]
 pub struct GrpcRoute(pub ParentRef, pub RouteRef);
@@ -54,17 +55,18 @@ pub enum Error {
 
 // === impl HttpRoute ===
 
-impl From<(ParentRef, RouteRef)> for HttpRoute {
-    fn from((parent, route): (ParentRef, RouteRef)) -> Self {
-        Self(parent, route)
+impl From<(ParentRef, RouteRef, Option<Host>)> for HttpRoute {
+    fn from((parent, route, host): (ParentRef, RouteRef, Option<Host>)) -> Self {
+        Self(parent, route, host)
     }
 }
 
 impl EncodeLabelSetMut for HttpRoute {
     fn encode_label_set(&self, enc: &mut LabelSetEncoder<'_>) -> std::fmt::Result {
-        let Self(parent, route) = self;
+        let Self(parent, route, host) = self;
         parent.encode_label_set(enc)?;
         route.encode_label_set(enc)?;
+        ("hostname", host.as_deref().unwrap_or("unknown")).encode(enc.encode_label())?;
         Ok(())
     }
 }