router: add x-envoy-attempt-count on downstream responses (#10325)

Description: this PR adds the `x-envoy-attempt-count` header to downstream responses.
Risk Level: low, used via new config value that defaults to false.
Testing: updated tests to verify that the header is being set. New unit tests
Docs Changes: updated docs
Release Notes: added.

Signed-off-by: Jose Nino <jnino@lyft.com>

Mirrored from https://github.com/envoyproxy/envoy @ 1db15db60af37b167b72e3c5e653ffdda9711336

envoy/api/v2/route/route_components.proto

@@ -32,7 +32,7 @@ option (udpa.annotations.file_migrate).move_to_package = "envoy.config.route.v3"
 // host header. This allows a single listener to service multiple top level domain path trees. Once
 // a virtual host is selected based on the domain, the routes are processed in order to see which
 // upstream cluster to route to or whether to perform a redirect.
-// [#next-free-field: 19]
+// [#next-free-field: 20]
 message VirtualHost {
   enum TlsRequirementType {
     // No TLS requirement for the virtual host.
@@ -143,8 +143,20 @@ message VirtualHost {
   // This header is unaffected by the
   // :ref:`suppress_envoy_headers
   // <envoy_api_field_config.filter.http.router.v2.Router.suppress_envoy_headers>` flag.
+  //
+  // [#next-major-version: rename to include_attempt_count_in_request.]
   bool include_request_attempt_count = 14;
 
+  // Decides whether the :ref:`x-envoy-attempt-count
+  // <config_http_filters_router_x-envoy-attempt-count>` header should be included
+  // in the downstream response. Setting this option will cause the router to override any existing header
+  // value, so in the case of two Envoys on the request path with this option enabled, the downstream
+  // will see the attempt count as perceived by the Envoy closest upstream from itself. Defaults to false.
+  // This header is unaffected by the
+  // :ref:`suppress_envoy_headers
+  // <envoy_api_field_config.filter.http.router.v2.Router.suppress_envoy_headers>` flag.
+  bool include_attempt_count_in_response = 19;
+
   // Indicates the retry policy for all routes in this virtual host. Note that setting a
   // route level entry will take precedence over this config and it'll be treated
   // independently (e.g.: values are not inherited).

envoy/config/route/v3/route_components.proto

@@ -32,7 +32,7 @@ option java_multiple_files = true;
 // host header. This allows a single listener to service multiple top level domain path trees. Once
 // a virtual host is selected based on the domain, the routes are processed in order to see which
 // upstream cluster to route to or whether to perform a redirect.
-// [#next-free-field: 19]
+// [#next-free-field: 20]
 message VirtualHost {
   option (udpa.annotations.versioning).previous_message_type = "envoy.api.v2.route.VirtualHost";
 
@@ -140,8 +140,20 @@ message VirtualHost {
   // This header is unaffected by the
   // :ref:`suppress_envoy_headers
   // <envoy_api_field_extensions.filters.http.router.v3.Router.suppress_envoy_headers>` flag.
+  //
+  // [#next-major-version: rename to include_attempt_count_in_request.]
   bool include_request_attempt_count = 14;
 
+  // Decides whether the :ref:`x-envoy-attempt-count
+  // <config_http_filters_router_x-envoy-attempt-count>` header should be included
+  // in the downstream response. Setting this option will cause the router to override any existing header
+  // value, so in the case of two Envoys on the request path with this option enabled, the downstream
+  // will see the attempt count as perceived by the Envoy closest upstream from itself. Defaults to false.
+  // This header is unaffected by the
+  // :ref:`suppress_envoy_headers
+  // <envoy_api_field_extensions.filters.http.router.v3.Router.suppress_envoy_headers>` flag.
+  bool include_attempt_count_in_response = 19;
+
   // Indicates the retry policy for all routes in this virtual host. Note that setting a
   // route level entry will take precedence over this config and it'll be treated
   // independently (e.g.: values are not inherited).