Add gRPC MaxConcurrentStreams limit and flag (#679)

Plausibly this should be in weaveworks/common/server, but I wanted to
try it out more locally first.

Author: bboreham

cmd/ingester/main.go

@@ -32,16 +32,22 @@ func main() {
 		storageConfig    storage.Config
 		ingesterConfig   ingester.Config
 		logLevel         util.LogLevel
+		maxStreams       uint
 	)
 	// Ingester needs to know our gRPC listen port.
 	ingesterConfig.ListenPort = &serverConfig.GRPCListenPort
 	util.RegisterFlags(&serverConfig, &chunkStoreConfig, &storageConfig,
 		&schemaConfig, &ingesterConfig, &logLevel)
+	flag.UintVar(&maxStreams, "ingester.max-concurrent-streams", 1000, "Limit on the number of concurrent streams for gRPC calls (0 = unlimited)")
 	flag.Parse()
 	schemaConfig.MaxChunkAge = ingesterConfig.MaxChunkAge
 
 	util.InitLogger(logLevel.AllowedLevel)
 
+	if maxStreams > 0 {
+		serverConfig.GRPCOptions = append(serverConfig.GRPCOptions, grpc.MaxConcurrentStreams(uint32(maxStreams)))
+	}
+
 	server, err := server.New(serverConfig)
 	if err != nil {
 		level.Error(util.Logger).Log("msg", "error initializing server", "err", err)