upstream: remove upstream_host_weight_change_causes_rebuild runtime

docs/root/version_history/current.rst

@@ -23,6 +23,7 @@ Removed Config or Runtime
 * compression: removed ``envoy.reloadable_features.enable_compression_without_content_length_header`` runtime guard and legacy code paths.
 * http: removed ``envoy.reloadable_features.return_502_for_upstream_protocol_errors``. Envoy will always return 502 code upon encountering upstream protocol error.
 * http: removed ``envoy.reloadable_features.treat_upstream_connect_timeout_as_connect_failure`` and legacy code paths.
+* upstream: removed ``envoy.reloadable_features.upstream_host_weight_change_causes_rebuild`` and legacy code paths.
 
 New Features
 ------------

source/common/runtime/runtime_features.cc

@@ -90,7 +90,6 @@ constexpr const char* runtime_features[] = {
     "envoy.reloadable_features.udp_listener_updates_filter_chain_in_place",
     "envoy.reloadable_features.udp_per_event_loop_read_limit",
     "envoy.reloadable_features.unquote_log_string_values",
-    "envoy.reloadable_features.upstream_host_weight_change_causes_rebuild",
     "envoy.reloadable_features.use_observable_cluster_name",
     "envoy.reloadable_features.validate_connect",
     "envoy.reloadable_features.vhds_heartbeats",

source/common/upstream/upstream_impl.cc

@@ -1607,14 +1607,11 @@ bool BaseDynamicClusterImpl::updateDynamicHostList(
       }
       if (existing_host->second->weight() != host->weight()) {
         existing_host->second->weight(host->weight());
-        if (Runtime::runtimeFeatureEnabled(
-                "envoy.reloadable_features.upstream_host_weight_change_causes_rebuild")) {
-          // We do full host set rebuilds so that load balancers can do pre-computation of data
-          // structures based on host weight. This may become a performance problem in certain
-          // deployments so it is runtime feature guarded and may also need to be configurable
-          // and/or dynamic in the future.
-          hosts_changed = true;
-        }
+        // We do full host set rebuilds so that load balancers can do pre-computation of data
+        // structures based on host weight. This may become a performance problem in certain
+        // deployments so it is runtime feature guarded and may also need to be configurable
+        // and/or dynamic in the future.
+        hosts_changed = true;
       }
 
       hosts_changed |=

test/common/upstream/eds_test.cc

@@ -355,9 +355,8 @@ TEST_F(EdsTest, EdsClusterFromFileIsPrimaryCluster) {
   EXPECT_TRUE(initialized_);
 }
 
-namespace {
-
-void endpointWeightChangeCausesRebuildTest(EdsTest& test, bool expect_rebuild) {
+// Verify that host weight changes cause a full rebuild.
+TEST_F(EdsTest, EndpointWeightChangeCausesRebuild) {
   envoy::config::endpoint::v3::ClusterLoadAssignment cluster_load_assignment;
   cluster_load_assignment.set_cluster_name("fare");
   auto* endpoints = cluster_load_assignment.add_endpoints();
@@ -366,45 +365,28 @@ void endpointWeightChangeCausesRebuildTest(EdsTest& test, bool expect_rebuild) {
   endpoint->mutable_endpoint()->mutable_address()->mutable_socket_address()->set_port_value(80);
   endpoint->mutable_load_balancing_weight()->set_value(30);
 
-  test.initialize();
-  test.doOnConfigUpdateVerifyNoThrow(cluster_load_assignment);
-  EXPECT_TRUE(test.initialized_);
-  EXPECT_EQ(0UL, test.stats_.counter("cluster.name.update_no_rebuild").value());
-  EXPECT_EQ(30UL,
-            test.stats_.gauge("cluster.name.max_host_weight", Stats::Gauge::ImportMode::Accumulate)
-                .value());
-  auto& hosts = test.cluster_->prioritySet().hostSetsPerPriority()[0]->hosts();
+  initialize();
+  doOnConfigUpdateVerifyNoThrow(cluster_load_assignment);
+  EXPECT_TRUE(initialized_);
+  EXPECT_EQ(0UL, stats_.counter("cluster.name.update_no_rebuild").value());
+  EXPECT_EQ(
+      30UL,
+      stats_.gauge("cluster.name.max_host_weight", Stats::Gauge::ImportMode::Accumulate).value());
+  auto& hosts = cluster_->prioritySet().hostSetsPerPriority()[0]->hosts();
   EXPECT_EQ(hosts.size(), 1);
   EXPECT_EQ(hosts[0]->weight(), 30);
 
   endpoint->mutable_load_balancing_weight()->set_value(31);
-  test.doOnConfigUpdateVerifyNoThrow(cluster_load_assignment);
-  EXPECT_EQ(expect_rebuild ? 0UL : 1UL,
-            test.stats_.counter("cluster.name.update_no_rebuild").value());
-  EXPECT_EQ(31UL,
-            test.stats_.gauge("cluster.name.max_host_weight", Stats::Gauge::ImportMode::Accumulate)
-                .value());
-  auto& new_hosts = test.cluster_->prioritySet().hostSetsPerPriority()[0]->hosts();
+  doOnConfigUpdateVerifyNoThrow(cluster_load_assignment);
+  EXPECT_EQ(0UL, stats_.counter("cluster.name.update_no_rebuild").value());
+  EXPECT_EQ(
+      31UL,
+      stats_.gauge("cluster.name.max_host_weight", Stats::Gauge::ImportMode::Accumulate).value());
+  auto& new_hosts = cluster_->prioritySet().hostSetsPerPriority()[0]->hosts();
   EXPECT_EQ(new_hosts.size(), 1);
   EXPECT_EQ(new_hosts[0]->weight(), 31);
 }
 
-} // namespace
-
-// Verify that host weight changes cause a full rebuild.
-TEST_F(EdsTest, EndpointWeightChangeCausesRebuild) {
-  endpointWeightChangeCausesRebuildTest(*this, true);
-}
-
-// Verify that host weight changes do not cause a full rebuild when the feature flag is disabled.
-TEST_F(EdsTest, EndpointWeightChangeCausesRebuildDisabled) {
-  TestScopedRuntime scoped_runtime;
-  Runtime::LoaderSingleton::getExisting()->mergeValues(
-      {{"envoy.reloadable_features.upstream_host_weight_change_causes_rebuild", "false"}});
-
-  endpointWeightChangeCausesRebuildTest(*this, false);
-}
-
 // Validate that onConfigUpdate() updates the endpoint metadata.
 TEST_F(EdsTest, EndpointMetadata) {
   envoy::config::endpoint::v3::ClusterLoadAssignment cluster_load_assignment;