Add support for drop category policy and reporting (#3894)

This PR contains changes to implement feature requested in issue #3823
 - Adding DropOverload in eds policy which can be used to specify
 drop_percentage per category.
 - Adding DroppedRequests in load_report which can report deliberately
 dropped requests for each category.

Signed-off-by: vishalpowar <vishal.powar@gmail.com>

Mirrored from https://github.com/envoyproxy/envoy @ 3ee3aa34d826fa1783c201fbf99dfec3a21eed53

envoy/api/v2/BUILD

@@ -40,6 +40,7 @@ api_proto_library_internal(
         "//envoy/api/v2/core:base",
         "//envoy/api/v2/core:health_check",
         "//envoy/api/v2/endpoint",
+        "//envoy/type:percent",
     ],
 )
 
@@ -52,6 +53,7 @@ api_go_grpc_library(
         "//envoy/api/v2/core:base_go_proto",
         "//envoy/api/v2/core:health_check_go_proto",
         "//envoy/api/v2/endpoint:endpoint_go_proto",
+        "//envoy/type:percent_go_proto",
     ],
 )
 

envoy/api/v2/eds.proto

@@ -6,6 +6,7 @@ option java_generic_services = true;
 
 import "envoy/api/v2/discovery.proto";
 import "envoy/api/v2/endpoint/endpoint.proto";
+import "envoy/type/percent.proto";
 
 import "google/api/annotations.proto";
 
@@ -50,12 +51,35 @@ message ClusterLoadAssignment {
 
   // Load balancing policy settings.
   message Policy {
-    // Percentage of traffic (0-100) that should be dropped. This
-    // action allows protection of upstream hosts should they unable to
-    // recover from an outage or should they be unable to autoscale and hence
-    // overall incoming traffic volume need to be trimmed to protect them.
-    // [#v2-api-diff: This is known as maintenance mode in v1.]
-    double drop_overload = 1 [(validate.rules).double = {gte: 0, lte: 100}];
+    reserved 1;
+
+    message DropOverload {
+      // Identifier for the policy specifying the drop.
+      string category = 1 [(validate.rules).string.min_bytes = 1];
+
+      // Percentage of traffic that should be dropped for the category.
+      envoy.type.Percent drop_percentage = 2;
+    }
+    // Action to trim the overall incoming traffic to protect the upstream
+    // hosts. This action allows protection in case the hosts are unable to
+    // recover from an outage, or unable to autoscale or unable to handle
+    // incoming traffic volume for any reason.
+    //
+    // At the client each category is applied one after the other to generate
+    // the 'actual' drop percentage on all outgoing traffic. For example:
+    //
+    // .. code-block:: json
+    //
+    //  { "drop_overloads": [
+    //      { "category": "throttle", "drop_percentage": 60 }
+    //      { "category": "lb", "drop_percentage": 50 }
+    //  ]}
+    //
+    // The actual drop percentages applied to the traffic at the clients will be
+    //    "throttle"_drop = 60%
+    //    "lb"_drop = 20%  // 50% of the remaining 'actual' load, which is 40%.
+    //    actual_outgoing_load = 20% // remaining after applying all categories.
+    repeated DropOverload drop_overloads = 2;
   }
 
   // Load balancing policy settings.

envoy/api/v2/endpoint/load_report.proto

@@ -96,6 +96,16 @@ message ClusterStats {
   // deliberately dropped by the drop_overload policy and circuit breaking.
   uint64 total_dropped_requests = 3;
 
+  message DroppedRequests {
+    // Identifier for the policy specifying the drop.
+    string category = 1 [(validate.rules).string.min_bytes = 1];
+    // Total number of deliberately dropped requests for the category.
+    uint64 dropped_count = 2;
+  }
+  // Information about deliberately dropped requests for each category specified
+  // in the DropOverload policy.
+  repeated DroppedRequests dropped_requests = 5;
+
   // Period over which the actual load report occurred. This will be guaranteed to include every
   // request reported. Due to system load and delays between the *LoadStatsRequest* sent from Envoy
   // and the *LoadStatsResponse* message sent from the management server, this may be longer than