cds: Configure LRS in CDS response

api/envoy/api/v2/cds.proto

@@ -52,7 +52,7 @@ service ClusterDiscoveryService {
 // [#protodoc-title: Clusters]
 
 // Configuration for a single upstream cluster.
-// [#comment:next free field: 42]
+// [#comment:next free field: 43]
 message Cluster {
   // Supplies the name of the cluster which must be unique across all clusters.
   // The cluster name is used when emitting
@@ -657,6 +657,35 @@ message Cluster {
   // :ref:`lb_policy<envoy_api_field_Cluster.lb_policy>` field has the value
   // :ref:`LOAD_BALANCING_POLICY_CONFIG<envoy_api_enum_value_Cluster.LbPolicy.LOAD_BALANCING_POLICY_CONFIG>`.
   LoadBalancingPolicy load_balancing_policy = 41;
+
+  // [#not-implemented-hide:] If present, tells the client where to send load reports via LRS.
+  //
+  // If multiple clusters are configured to use the same LRS server, then the data for all of
+  // those clusters may be sent on the same LRS stream.
+  //
+  // Note that if LRS is configured this way, then there is no need for the LRS server to send
+  // LoadStatsResponse messages on the LRS stream, because the data it would have sent is already
+  // configured here.
+  message LoadReportConfig {
+    // A management server endpoint to stream load stats to via
+    // *StreamLoadStats*. This must have :ref:`api_type
+    // <envoy_api_field_core.ApiConfigSource.api_type>` :ref:`GRPC
+    // <envoy_api_enum_value_core.ApiConfigSource.ApiType.GRPC>`.
+    core.ApiConfigSource lrs_server = 1;
+    // The minimum time interval to collect stats over. This is only a
+    // minimum for two reasons:
+    // 1. There may be some delay between when the timer fires and when
+    //    stats sampling occurs.
+    // 2. Whenever the load reporting interval for the cluster changes, any
+    //    traffic that is observed since the last load report for the
+    //    cluster will be included in the next load report. This avoids
+    //    a period of inobservability for the cluster.
+    google.protobuf.Duration load_reporting_interval = 2;
+    // If set to *true*, the client should generate endpoint-granularity
+    // load reports. Otherwise, load reports should be at locality granularity.
+    bool report_endpoint_granularity = 3;
+  }
+  LoadReportConfig load_report_config = 42;
 }
 
 // [#not-implemented-hide:] Extensible load balancing policy configuration.

api/envoy/service/load_stats/v2/lrs.proto

@@ -45,6 +45,12 @@ service LoadReportingService {
   // 6. The management server uses the load reports from all reported Envoys
   //    from around the world, computes global assignment and prepares traffic
   //    assignment destined for each zone Envoys are located in. Goto 2.
+  //
+  // Note: If the management server configured use of LRS via via the CDS
+  // :ref:`Cluster.load_report_config
+  // <envoy_api_field_Cluster.load_report_config>` field, then it will never
+  // send a response message on the stream. Instead, that data will
+  // come from the CDS response.
   rpc StreamLoadStats(stream LoadStatsRequest) returns (stream LoadStatsResponse) {
   }
 }

tools/spelling_dictionary.txt

@@ -150,6 +150,7 @@ LDS
 LEV
 LHS
 LF
+LRS
 MB
 MD
 MGET