cluster: adding host rewrite (envoyproxy#17083)

Risk Level: low (config guarded addition)
Testing: new unit tests
Docs Changes: in API docs
Release Notes: inline
Fixes envoyproxy#16775

Signed-off-by: Alyssa Wilk <[email protected]>

api/envoy/config/route/v3/route_components.proto

@@ -311,7 +311,7 @@ message Route {
 message WeightedCluster {
   option (udpa.annotations.versioning).previous_message_type = "envoy.api.v2.route.WeightedCluster";
 
-  // [#next-free-field: 11]
+  // [#next-free-field: 12]
   message ClusterWeight {
     option (udpa.annotations.versioning).previous_message_type =
         "envoy.api.v2.route.WeightedCluster.ClusterWeight";
@@ -378,6 +378,13 @@ message WeightedCluster {
     // :ref:`FilterConfig<envoy_v3_api_msg_config.route.v3.FilterConfig>`
     // message to specify additional options.]
     map<string, google.protobuf.Any> typed_per_filter_config = 10;
+
+    oneof host_rewrite_specifier {
+      // Indicates that during forwarding, the host header will be swapped with
+      // this value.
+      string host_rewrite_literal = 11
+          [(validate.rules).string = {well_known_regex: HTTP_HEADER_VALUE strict: false}];
+    }
   }
 
   // Specifies one or more upstream clusters associated with the route.

docs/root/version_history/current.rst

@@ -83,6 +83,7 @@ New Features
 * bandwidth_limit: added new :ref:`HTTP bandwidth limit filter <config_http_filters_bandwidth_limit>`.
 * bootstrap: added :ref:`dns_resolution_config <envoy_v3_api_field_config.bootstrap.v3.Bootstrap.dns_resolution_config>` to aggregate all of the DNS resolver configuration in a single message. By setting one such configuration option ``no_default_search_domain`` as true the DNS resolver will not use the default search domains. And by setting the configuration ``resolvers`` we can specify the external DNS servers to be used for external DNS query.
 * cluster: added :ref:`dns_resolution_config <envoy_v3_api_field_config.cluster.v3.Cluster.dns_resolution_config>` to aggregate all of the DNS resolver configuration in a single message. By setting one such configuration option ``no_default_search_domain`` as true the DNS resolver will not use the default search domains.
+* cluster: added :ref:`host_rewrite_literal <envoy_v3_api_field_config.route.v3.WeightedCluster.ClusterWeight.host_rewrite_literal>` to WeightedCluster.
 * composite filter: can now be used with filters that also add an access logger, such as the WASM filter.
 * config: added stat :ref:`config_reload_time_ms <subscription_statistics>`.
 * connection_limit: added new :ref:`Network connection limit filter <config_network_filters_connection_limit>`.

source/common/router/config_impl.cc

@@ -1021,7 +1021,8 @@ RouteEntryImplBase::WeightedClusterEntry::WeightedClusterEntry(
                                                        cluster.response_headers_to_remove())),
       per_filter_configs_(cluster.typed_per_filter_config(),
                           cluster.hidden_envoy_deprecated_per_filter_config(),
-                          optional_http_filters, factory_context, validator) {
+                          optional_http_filters, factory_context, validator),
+      host_rewrite_(cluster.host_rewrite_literal()) {
   if (cluster.has_metadata_match()) {
     const auto filter_it = cluster.metadata_match().filter_metadata().find(
         Envoy::Config::MetadataFilters::get().ENVOY_LB);

source/common/router/config_impl.h

@@ -771,6 +771,9 @@ class RouteEntryImplBase : public RouteEntry,
                                 const StreamInfo::StreamInfo& stream_info,
                                 bool insert_envoy_original_path) const override {
       request_headers_parser_->evaluateHeaders(headers, stream_info);
+      if (!host_rewrite_.empty()) {
+        headers.setHost(host_rewrite_);
+      }
       DynamicRouteEntry::finalizeRequestHeaders(headers, stream_info, insert_envoy_original_path);
     }
     void finalizeResponseHeaders(Http::ResponseHeaderMap& headers,
@@ -791,6 +794,7 @@ class RouteEntryImplBase : public RouteEntry,
     HeaderParserPtr request_headers_parser_;
     HeaderParserPtr response_headers_parser_;
     PerFilterConfigs per_filter_configs_;
+    const std::string host_rewrite_;
   };
 
   using WeightedClusterEntrySharedPtr = std::shared_ptr<WeightedClusterEntry>;

test/common/router/config_impl_test.cc

@@ -5202,6 +5202,7 @@ TEST_F(RouteMatcherTest, TestWeightedClusterHeaderManipulation) {
                       key: x-resp-cluster
                       value: cluster1
                 response_headers_to_remove: [ "x-remove-cluster1" ]
+                host_rewrite_literal: "new_host1"
               - name: cluster2
                 weight: 50
                 request_headers_to_add:
@@ -5227,6 +5228,7 @@ TEST_F(RouteMatcherTest, TestWeightedClusterHeaderManipulation) {
 
     route->finalizeRequestHeaders(headers, stream_info, true);
     EXPECT_EQ("cluster1", headers.get_("x-req-cluster"));
+    EXPECT_EQ("new_host1", headers.getHostValue());
 
     route->finalizeResponseHeaders(resp_headers, stream_info);
     EXPECT_EQ("cluster1", resp_headers.get_("x-resp-cluster"));