docs: release notes and unhide fields for locality based balancing.

docs/root/intro/arch_overview/load_balancing.rst

@@ -59,6 +59,11 @@ currently support weighting.
 When priority based load balancing is in use, the priority level is also chosen by hash, so the
 endpoint selected will still be consistent when the set of backends is stable.
 
+.. note::
+
+  The ring hash load balancer does not support :ref:`locality weighted load
+  balancing <arch_overview_load_balancing_locality_weighted_lb>`.
+
 .. _arch_overview_load_balancing_types_maglev:
 
 Maglev
@@ -309,6 +314,17 @@ picked. The load balancer follows these steps:
 2. Pick locality (as described in this section) within priority level from (1).
 3. Pick endpoint using cluster specified load balancer within locality from (2).
 
+Locality weighted load balancing is configured by setting
+:ref:`locality_weighted_lb_config
+<envoy_api_field_Cluster.CommonLbConfig.locality_weighted_lb_config>` in the
+cluster configuration and providing weights in :ref:`LocalityLbEndpoints
+<envoy_api_msg_endpoint.LocalityLbEndpoints>` via :ref:`load_balancing_weight
+<envoy_api_field_endpoint.LocalityLbEndpoints.load_balancing_weight>`.
+
+This feature is not compatible with :ref:`load balancer subsetting
+<arch_overview_load_balancer_subsets>`, since it is not straightforward to
+reconcile locality level weighting with sensible weights for individual subsets.
+
 .. _arch_overview_load_balancer_subsets:
 
 Load Balancer Subsets

docs/root/intro/version_history.rst

@@ -23,6 +23,8 @@ Version history
   <arch_overview_load_balancing_types_round_robin>` support. The round robin
   scheduler now respects endpoint weights and also has improved fidelity across
   picks.
+* load balancer: :ref:`Locality weighted load balancing
+  <arch_overview_load_balancer_subsets>` is now supported.
 * logger: added the ability to optionally set the log format via the :option:`--log-format` option.
 * logger: all :ref:`logging levels <operations_admin_interface_logging>` can be configured
   at run-time: trace debug info warning error critical.

envoy/api/v2/cds.proto

@@ -394,13 +394,11 @@ message Cluster {
     }
     // Configuration for :ref:`locality weighted load balancing
     // <arch_overview_load_balancing_locality_weighted_lb>`
-    // [#not-implemented-hide:]
     message LocalityWeightedLbConfig {
     }
     oneof locality_config_specifier {
       // [#not-implemented-hide:]
       ZoneAwareLbConfig zone_aware_lb_config = 2;
-      // [#not-implemented-hide:]
       LocalityWeightedLbConfig locality_weighted_lb_config = 3;
     }
   }