xds: add config for least_request LB policy extension (#21210)

Signed-off-by: Terry Wilson <[email protected]>

api/envoy/extensions/load_balancing_policies/least_request/v3/BUILD

@@ -0,0 +1,13 @@
+# DO NOT EDIT. This file is generated by tools/proto_format/proto_sync.py.
+
+load("@envoy_api//bazel:api_build_system.bzl", "api_proto_package")
+
+licenses(["notice"])  # Apache 2
+
+api_proto_package(
+    deps = [
+        "//envoy/config/cluster/v3:pkg",
+        "//envoy/config/core/v3:pkg",
+        "@com_github_cncf_udpa//udpa/annotations:pkg",
+    ],
+)

api/envoy/extensions/load_balancing_policies/least_request/v3/least_request.proto

@@ -0,0 +1,58 @@
+syntax = "proto3";
+
+package envoy.extensions.load_balancing_policies.least_request.v3;
+
+import "envoy/config/cluster/v3/cluster.proto";
+import "envoy/config/core/v3/base.proto";
+
+import "google/protobuf/wrappers.proto";
+
+import "udpa/annotations/status.proto";
+import "validate/validate.proto";
+
+option java_package = "io.envoyproxy.envoy.extensions.load_balancing_policies.least_request.v3";
+option java_outer_classname = "LeastRequestProto";
+option java_multiple_files = true;
+option go_package = "github.com/envoyproxy/go-control-plane/envoy/extensions/load_balancing_policies/least_request/v3;least_requestv3";
+option (udpa.annotations.file_status).package_version_status = ACTIVE;
+
+// [#protodoc-title: Least Request Load Balancing Policy]
+
+// This configuration allows the built-in LEAST_REQUEST LB policy to be configured via the LB policy
+// extension point. See the :ref:`load balancing architecture overview
+// <arch_overview_load_balancing_types>` for more information.
+// [#extension: envoy.clusters.lb_policy]
+message LeastRequest {
+  // The number of random healthy hosts from which the host with the fewest active requests will
+  // be chosen. Defaults to 2 so that we perform two-choice selection if the field is not set.
+  google.protobuf.UInt32Value choice_count = 1 [(validate.rules).uint32 = {gte: 2}];
+
+  // The following formula is used to calculate the dynamic weights when hosts have different load
+  // balancing weights:
+  //
+  // `weight = load_balancing_weight / (active_requests + 1)^active_request_bias`
+  //
+  // The larger the active request bias is, the more aggressively active requests will lower the
+  // effective weight when all host weights are not equal.
+  //
+  // `active_request_bias` must be greater than or equal to 0.0.
+  //
+  // When `active_request_bias == 0.0` the Least Request Load Balancer doesn't consider the number
+  // of active requests at the time it picks a host and behaves like the Round Robin Load
+  // Balancer.
+  //
+  // When `active_request_bias > 0.0` the Least Request Load Balancer scales the load balancing
+  // weight by the number of active requests at the time it does a pick.
+  //
+  // The value is cached for performance reasons and refreshed whenever one of the Load Balancer's
+  // host sets changes, e.g., whenever there is a host membership update or a host load balancing
+  // weight change.
+  //
+  // .. note::
+  //   This setting only takes effect if all host weights are not equal.
+  config.core.v3.RuntimeDouble active_request_bias = 2;
+
+  // Configuration for slow start mode.
+  // If this configuration is not set, slow start will not be not enabled.
+  config.cluster.v3.Cluster.SlowStartConfig slow_start_config = 3;
+}

api/versioning/BUILD

@@ -165,6 +165,7 @@ proto_library(
         "//envoy/extensions/internal_redirect/previous_routes/v3:pkg",
         "//envoy/extensions/internal_redirect/safe_cross_scheme/v3:pkg",
         "//envoy/extensions/key_value/file_based/v3:pkg",
+        "//envoy/extensions/load_balancing_policies/least_request/v3:pkg",
         "//envoy/extensions/load_balancing_policies/ring_hash/v3:pkg",
         "//envoy/extensions/load_balancing_policies/round_robin/v3:pkg",
         "//envoy/extensions/load_balancing_policies/wrr_locality/v3:pkg",