service config and channelz changes for connection scaling (#171)

* add connection scaling message to service config

* add connection scaling fields in channelz

* add reference to gRFC A105

Author: markdroth

grpc/channelz/v1/channelz.proto

@@ -115,6 +115,9 @@ message ChannelData {
 
   // The last time a call was started on the channel.
   google.protobuf.Timestamp last_call_started_timestamp = 7;
+
+  // Populated for subchannels only.
+  uint32 max_connections_per_subchannel = 8;
 }
 
 // A trace event is an interesting thing that happened to a channel or
@@ -292,6 +295,14 @@ message SocketData {
   // Socket options set on this socket.  May be absent if 'summary' is set
   // on GetSocketRequest.
   repeated SocketOption option = 13;
+
+  // Populated if a GOAWAY has been received.  The value will be the
+  // HTTP/2 error code from the GOAWAY.
+  google.protobuf.UInt32Value received_goaway_error = 14;
+
+  // The value of MAX_CONCURRENT_STREAMS set by the peer.  Populated on
+  // client side only.
+  uint32 peer_max_concurrent_streams = 15;
 }
 
 // Address represents the address used to create the socket.

grpc/service_config/service_config.proto

@@ -641,7 +641,25 @@ message ServiceConfig {
   }
   HealthCheckConfig health_check_config = 5;
 
-  // next available tag: 6
+  // Settings to control dynamic connection scaling.  For details, see:
+  // https://github.com/grpc/proposal/blob/master/A105-max_concurrent_streams-connection-scaling.md
+  message ConnectionScaling {
+    // Maximum connections gRPC will maintain for each subchannel in
+    // this channel.  When no streams are available for an RPC in a
+    // subchannel, gRPC will automatically create new connections up
+    // to this limit.  If this value changes during the life of a
+    // channel, existing subchannels will be updated to reflect
+    // the change.  No connections will be closed as a result of
+    // lowering this value; down-scaling will only happen as
+    // connections are lost naturally.
+    //
+    // Values higher than the client-enforced limit (by default, 10)
+    // will be clamped to that limit.
+    google.protobuf.UInt32Value max_connections_per_subchannel = 1;
+  }
+  ConnectionScaling connection_scaling = 6;
+
+  // next available tag: 7
 }
 
 //