router: add x-envoy-attempt-count on downstream responses

api/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).

api/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).

docs/root/configuration/http/http_filters/router_filter.rst

@@ -36,8 +36,8 @@ or :ref:`config_http_filters_router_x-envoy-retry-grpc-on` headers are not speci
 A few notes on how Envoy does retries:
 
 * The route timeout (set via :ref:`config_http_filters_router_x-envoy-upstream-rq-timeout-ms` or the
-  :ref:`timeout <envoy_api_field_route.RouteAction.timeout>` in route configuration or set via 
-  `grpc-timeout header <https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md>`_  by specifying 
+  :ref:`timeout <envoy_api_field_route.RouteAction.timeout>` in route configuration or set via
+  `grpc-timeout header <https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md>`_  by specifying
   :ref:`max_grpc_timeout <envoy_api_field_route.RouteAction.timeout>` in route configuration) **includes** all
   retries. Thus if the request timeout is set to 3s, and the first request attempt takes 2.7s, the
   retry (including back-off) has .3s to complete. This is by design to avoid an exponential
@@ -232,8 +232,8 @@ x-envoy-upstream-rq-timeout-ms
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Setting this header on egress requests will cause Envoy to override the :ref:`route configuration timeout
-<envoy_api_field_route.RouteAction.timeout>` or gRPC client timeout set via `grpc-timeout header 
-<https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md>`_  by specifying :ref:`max_grpc_timeout 
+<envoy_api_field_route.RouteAction.timeout>` or gRPC client timeout set via `grpc-timeout header
+<https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md>`_  by specifying :ref:`max_grpc_timeout
 <envoy_api_field_route.RouteAction.timeout>`. The timeout must be specified in millisecond
 units. See also :ref:`config_http_filters_router_x-envoy-upstream-rq-per-try-timeout-ms`.
 
@@ -319,7 +319,13 @@ x-envoy-attempt-count
 
 Sent to the upstream to indicate which attempt the current request is in a series of retries. The value
 will be "1" on the initial request, incrementing by one for each retry. Only set if the
-:ref:`include_attempt_count_header <envoy_api_field_route.VirtualHost.include_request_attempt_count>`
+:ref:`include_request_attempt_count <envoy_api_field_route.VirtualHost.include_request_attempt_count>`
+flag is set to true.
+
+Sent to the downstream to indicate how many upstream requests took place. The header will be absent if
+the router did not send any upstream requests. The value will be "1" if only the original upstream
+request was sent, incrementing by one for each retry. Only set if the
+:ref:`include_attempt_count_in_response <envoy_api_field_route.VirtualHost.include_attempt_count_in_response>`
 flag is set to true.
 
 .. _config_http_filters_router_x-envoy-expected-rq-timeout-ms:

docs/root/intro/version_history.rst

@@ -41,6 +41,8 @@ Version history
 * router: added support for :ref:`regex_rewrite
   <envoy_api_field_route.RouteAction.regex_rewrite>` for path rewriting using regular expressions and capture groups.
 * router: don't ignore :ref:`per_try_timeout <envoy_api_field_route.RetryPolicy.per_try_timeout>` when the :ref:`global route timeout <envoy_api_field_route.RouteAction.timeout>` is disabled.
+* router: added ability to set attempt count in downstream response, see :ref:`virtual host's include response
+  attempt count config <envoy_api_field_route.VirtualHost.include_attempt_count_in_response>`.
 * router: strip whitespace for :ref:`retry_on <envoy_api_field_route.RetryPolicy.retry_on>`, :ref:`grpc-retry-on header <config_http_filters_router_x-envoy-retry-grpc-on>` and :ref:`retry-on header <config_http_filters_router_x-envoy-retry-on>`.
 * runtime: enabling the runtime feature "envoy.deprecated_features.allow_deprecated_extension_names"
   disables the use of deprecated extension names.

include/envoy/http/header_map.h

@@ -274,7 +274,6 @@ class HeaderEntry {
   HEADER_FUNC(AccessControlRequestMethod)                                                          \
   HEADER_FUNC(Authorization)                                                                       \
   HEADER_FUNC(ClientTraceId)                                                                       \
-  HEADER_FUNC(EnvoyAttemptCount)                                                                   \
   HEADER_FUNC(EnvoyDownstreamServiceCluster)                                                       \
   HEADER_FUNC(EnvoyDownstreamServiceNode)                                                          \
   HEADER_FUNC(EnvoyExpectedRequestTimeoutMs)                                                       \
@@ -344,6 +343,7 @@ class HeaderEntry {
   HEADER_FUNC(Connection)                                                                          \
   HEADER_FUNC(ContentLength)                                                                       \
   HEADER_FUNC(ContentType)                                                                         \
+  HEADER_FUNC(EnvoyAttemptCount)                                                                   \
   HEADER_FUNC(EnvoyDecoratorOperation)                                                             \
   HEADER_FUNC(KeepAlive)                                                                           \
   HEADER_FUNC(NoChunks)                                                                            \

include/envoy/router/router.h

@@ -443,7 +443,12 @@ class VirtualHost {
   /**
    * @return bool whether to include the request count header in upstream requests.
    */
-  virtual bool includeAttemptCount() const PURE;
+  virtual bool includeAttemptCountInRequest() const PURE;
+
+  /**
+   * @return bool whether to include the request count header in the downstream response.
+   */
+  virtual bool includeAttemptCountInResponse() const PURE;
 
   /**
    * @return uint32_t any route cap on bytes which should be buffered for shadowing or retries.
@@ -778,7 +783,14 @@ class RouteEntry : public ResponseEntry {
    * count header.
    * @return bool whether x-envoy-attempt-count should be included on the upstream request.
    */
-  virtual bool includeAttemptCount() const PURE;
+  virtual bool includeAttemptCountInRequest() const PURE;
+
+  /**
+   * True if the virtual host this RouteEntry belongs to is configured to include the attempt
+   * count header.
+   * @return bool whether x-envoy-attempt-count should be included on the downstream response.
+   */
+  virtual bool includeAttemptCountInResponse() const PURE;
 
   using UpgradeMap = std::map<std::string, bool>;
   /**

source/common/http/async_client_impl.h

@@ -184,7 +184,8 @@ class AsyncStreamImpl : public AsyncClient::Stream,
     const Router::RouteSpecificFilterConfig* perFilterConfig(const std::string&) const override {
       return nullptr;
     }
-    bool includeAttemptCount() const override { return false; }
+    bool includeAttemptCountInRequest() const override { return false; }
+    bool includeAttemptCountInResponse() const override { return false; }
     uint32_t retryShadowBufferLimit() const override {
       return std::numeric_limits<uint32_t>::max();
     }
@@ -268,7 +269,8 @@ class AsyncStreamImpl : public AsyncClient::Stream,
       return nullptr;
     }
 
-    bool includeAttemptCount() const override { return false; }
+    bool includeAttemptCountInRequest() const override { return false; }
+    bool includeAttemptCountInResponse() const override { return false; }
     const Router::RouteEntry::UpgradeMap& upgradeMap() const override { return upgrade_map_; }
     Router::InternalRedirectAction internalRedirectAction() const override {
       return Router::InternalRedirectAction::PassThrough;

source/common/router/config_impl.cc

@@ -940,7 +940,8 @@ VirtualHostImpl::VirtualHostImpl(const envoy::config::route::v3::VirtualHost& vi
                           validator),
       retry_shadow_buffer_limit_(PROTOBUF_GET_WRAPPED_OR_DEFAULT(
           virtual_host, per_request_buffer_limit_bytes, std::numeric_limits<uint32_t>::max())),
-      include_attempt_count_(virtual_host.include_request_attempt_count()),
+      include_attempt_count_in_request_(virtual_host.include_request_attempt_count()),
+      include_attempt_count_in_response_(virtual_host.include_attempt_count_in_response()),
       virtual_cluster_catch_all_(stat_name_pool_) {
 
   switch (virtual_host.require_tls()) {

source/common/router/config_impl.h

@@ -174,7 +174,8 @@ class VirtualHostImpl : public VirtualHost {
   const RateLimitPolicy& rateLimitPolicy() const override { return rate_limit_policy_; }
   const Config& routeConfig() const override;
   const RouteSpecificFilterConfig* perFilterConfig(const std::string&) const override;
-  bool includeAttemptCount() const override { return include_attempt_count_; }
+  bool includeAttemptCountInRequest() const override { return include_attempt_count_in_request_; }
+  bool includeAttemptCountInResponse() const override { return include_attempt_count_in_response_; }
   const absl::optional<envoy::config::route::v3::RetryPolicy>& retryPolicy() const {
     return retry_policy_;
   }
@@ -223,7 +224,8 @@ class VirtualHostImpl : public VirtualHost {
   HeaderParserPtr response_headers_parser_;
   PerFilterConfigs per_filter_configs_;
   uint32_t retry_shadow_buffer_limit_{std::numeric_limits<uint32_t>::max()};
-  const bool include_attempt_count_;
+  const bool include_attempt_count_in_request_;
+  const bool include_attempt_count_in_response_;
   absl::optional<envoy::config::route::v3::RetryPolicy> retry_policy_;
   absl::optional<envoy::config::route::v3::HedgePolicy> hedge_policy_;
   const CatchAllVirtualCluster virtual_cluster_catch_all_;
@@ -451,7 +453,12 @@ class RouteEntryImplBase : public RouteEntry,
   const envoy::config::core::v3::Metadata& metadata() const override { return metadata_; }
   const Envoy::Config::TypedMetadata& typedMetadata() const override { return typed_metadata_; }
   const PathMatchCriterion& pathMatchCriterion() const override { return *this; }
-  bool includeAttemptCount() const override { return vhost_.includeAttemptCount(); }
+  bool includeAttemptCountInRequest() const override {
+    return vhost_.includeAttemptCountInRequest();
+  }
+  bool includeAttemptCountInResponse() const override {
+    return vhost_.includeAttemptCountInResponse();
+  }
   const UpgradeMap& upgradeMap() const override { return upgrade_map_; }
   InternalRedirectAction internalRedirectAction() const override {
     return internal_redirect_action_;
@@ -572,7 +579,12 @@ class RouteEntryImplBase : public RouteEntry,
       return parent_->pathMatchCriterion();
     }
 
-    bool includeAttemptCount() const override { return parent_->includeAttemptCount(); }
+    bool includeAttemptCountInRequest() const override {
+      return parent_->includeAttemptCountInRequest();
+    }
+    bool includeAttemptCountInResponse() const override {
+      return parent_->includeAttemptCountInResponse();
+    }
     const UpgradeMap& upgradeMap() const override { return parent_->upgradeMap(); }
     InternalRedirectAction internalRedirectAction() const override {
       return parent_->internalRedirectAction();