Overload Manager: Implement LoadShedPoint. (#26578)

* Implement  Overload Manager LoadShedPoint.

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ b824baf79e912b56cef5173566896a5e031af610

envoy/config/overload/v3/overload.proto

@@ -134,14 +134,37 @@ message OverloadAction {
   string name = 1 [(validate.rules).string = {min_len: 1}];
 
   // A set of triggers for this action. The state of the action is the maximum
-  // state of all triggers, which can be scaling between 0 and 1 or saturated. Listeners
-  // are notified when the overload action changes state.
+  // state of all triggers, which can be scalar values between 0 and 1 or
+  // saturated. Listeners are notified when the overload action changes state.
+  // An overload manager action can only have one trigger for a given resource
+  // e.g. :ref:`Trigger.name
+  // <envoy_v3_api_field_config.overload.v3.Trigger.name>` must be unique
+  // in this list.
   repeated Trigger triggers = 2 [(validate.rules).repeated = {min_items: 1}];
 
   // Configuration for the action being instantiated.
   google.protobuf.Any typed_config = 3;
 }
 
+// A point within the connection or request lifecycle that provides context on
+// whether to shed load at that given stage for the current entity at the
+// point.
+message LoadShedPoint {
+  // This is just a well-known string for the LoadShedPoint.
+  // Deployment specific LoadShedPoints e.g. within a custom extension should
+  // be prefixed by the company / deployment name to avoid colliding with any
+  // open source LoadShedPoints.
+  string name = 1 [(validate.rules).string = {min_len: 1}];
+
+  // A set of triggers for this LoadShedPoint. The LoadShedPoint will use the
+  // the maximum state of all triggers, which can be scalar values between 0 and
+  // 1 or saturated. A LoadShedPoint can only have one trigger for a given
+  // resource e.g. :ref:`Trigger.name
+  // <envoy_v3_api_field_config.overload.v3.Trigger.name>` must be unique in
+  // this list.
+  repeated Trigger triggers = 2 [(validate.rules).repeated = {min_items: 1}];
+}
+
 // Configuration for which accounts the WatermarkBuffer Factories should
 // track.
 message BufferFactoryConfig {
@@ -162,6 +185,7 @@ message BufferFactoryConfig {
   uint32 minimum_account_to_track_power_of_two = 1 [(validate.rules).uint32 = {lte: 56 gte: 10}];
 }
 
+// [#next-free-field: 6]
 message OverloadManager {
   option (udpa.annotations.versioning).previous_message_type =
       "envoy.config.overload.v2alpha.OverloadManager";
@@ -175,6 +199,10 @@ message OverloadManager {
   // The set of overload actions.
   repeated OverloadAction actions = 3;
 
+  // [#not-implemented-hide:]
+  // The set of load shed points.
+  repeated LoadShedPoint loadshed_points = 5;
+
   // Configuration for buffer factory.
   BufferFactoryConfig buffer_factory_config = 4;
 }