xds: add config for wrr_locality and round_robin LB policy extensions (#19517)

This PR adds two new LB policy extension configurations, to be used in gRPC via the new load_balancing_policy field:

* round_robin: This allows configuring the built-in ROUND_ROBIN LB policy via the new extension-based API.
* wrr_locality: This is an extension config for a new policy that does ROUND_ROBIN-style locality picking and then delegates to a child LB policy extension to pick the endpoint within the locality. This will allow users to plugin their own custom endpoint-picking logic without having to reimplement the locality-picking logic.

This is a small step toward moving away from the legacy lb_policy enum. Completing that migration will require work in Envoy to create extension configs for all built-in LB policies and register those extensions.

Risk Level: Low
Testing: N/A
Docs Changes: Included in PR
Release Notes: N/A
Platform Specific Features: N/A

Signed-off-by: Mark D. Roth <roth@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 65a82d75c3ef1e15fbc4f301c9eacc269a1a6080

envoy/extensions/load_balancing_policies/round_robin/v3/BUILD

@@ -0,0 +1,12 @@
+# 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",
+        "@com_github_cncf_udpa//udpa/annotations:pkg",
+    ],
+)

envoy/extensions/load_balancing_policies/round_robin/v3/round_robin.proto

@@ -0,0 +1,26 @@
+syntax = "proto3";
+
+package envoy.extensions.load_balancing_policies.round_robin.v3;
+
+import "envoy/config/cluster/v3/cluster.proto";
+
+import "udpa/annotations/status.proto";
+import "validate/validate.proto";
+
+option java_package = "io.envoyproxy.envoy.extensions.load_balancing_policies.round_robin.v3";
+option java_outer_classname = "RoundRobinProto";
+option java_multiple_files = true;
+option go_package = "github.com/envoyproxy/go-control-plane/envoy/extensions/load_balancing_policies/round_robin/v3;round_robinv3";
+option (udpa.annotations.file_status).package_version_status = ACTIVE;
+
+// [#protodoc-title: Round Robin Load Balancing Policy]
+
+// This configuration allows the built-in ROUND_ROBIN 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 RoundRobin {
+  // 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 = 1;
+}

envoy/extensions/load_balancing_policies/wrr_locality/v3/BUILD

@@ -0,0 +1,12 @@
+# 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",
+        "@com_github_cncf_udpa//udpa/annotations:pkg",
+    ],
+)

envoy/extensions/load_balancing_policies/wrr_locality/v3/wrr_locality.proto

@@ -0,0 +1,25 @@
+syntax = "proto3";
+
+package envoy.extensions.load_balancing_policies.wrr_locality.v3;
+
+import "envoy/config/cluster/v3/cluster.proto";
+
+import "udpa/annotations/status.proto";
+import "validate/validate.proto";
+
+option java_package = "io.envoyproxy.envoy.extensions.load_balancing_policies.wrr_locality.v3";
+option java_outer_classname = "WrrLocalityProto";
+option java_multiple_files = true;
+option go_package = "github.com/envoyproxy/go-control-plane/envoy/extensions/load_balancing_policies/wrr_locality/v3;wrr_localityv3";
+option (udpa.annotations.file_status).package_version_status = ACTIVE;
+
+// [#protodoc-title: Weighted Round Robin Locality-Picking Load Balancing Policy]
+
+// Configuration for the wrr_locality LB policy. See the :ref:`load balancing architecture overview
+// <arch_overview_load_balancing_types>` for more information.
+// [#extension: envoy.clusters.lb_policy]
+message WrrLocality {
+  // The child LB policy to create for endpoint-picking within the chosen locality.
+  config.cluster.v3.LoadBalancingPolicy endpoint_picking_policy = 1
+      [(validate.rules).message = {required: true}];
+}

versioning/BUILD

@@ -155,6 +155,8 @@ 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/round_robin/v3:pkg",
+        "//envoy/extensions/load_balancing_policies/wrr_locality/v3:pkg",
         "//envoy/extensions/matching/common_inputs/environment_variable/v3:pkg",
         "//envoy/extensions/matching/input_matchers/consistent_hashing/v3:pkg",
         "//envoy/extensions/matching/input_matchers/ip/v3:pkg",