servers: advertise the configured metricsPort to the master

Filer, S3 and broker report it on the KeepConnected registration, volume
servers in their heartbeat, and masters return their own in
GetMasterConfiguration. MasterClient gains SetMetricsPort so the eight
callers that have no metrics listener are untouched, and the volume
server takes it as a constructor argument because its heartbeat goroutine
starts there.

In combined "weed server" one metrics listener serves the whole shared
registry, so every component advertises the same port.

weed/s3api/s3api_server.go

@@ -65,10 +65,15 @@ type S3ApiServerOption struct {
 	Ip                        string // address advertised to the cluster; empty falls back to BindIp
 	BindIp                    string
 	GrpcPort                  int
-	ExternalUrl               string // external URL clients use, tried first during signature verification behind a reverse proxy
-	DefaultFileMode           uint32 // default file permission mode for S3 uploads (e.g. 0660, 0644)
-	CacheSizeMB               int64  // in-memory chunk cache capacity in MB for the shared ReaderCache; 0 disables
-	MaxMB                     int32  // filer's -maxMB, read from the filer configuration at startup
+	// MetricsPort is the Prometheus /metrics port this S3 server serves,
+	// advertised to the master so the admin server can scrape it. 0 when
+	// disabled. S3 metrics carry bucket labels, so they are deliberately not
+	// served on the client-facing S3 port.
+	MetricsPort     uint32
+	ExternalUrl     string // external URL clients use, tried first during signature verification behind a reverse proxy
+	DefaultFileMode uint32 // default file permission mode for S3 uploads (e.g. 0660, 0644)
+	CacheSizeMB     int64  // in-memory chunk cache capacity in MB for the shared ReaderCache; 0 disables
+	MaxMB           int32  // filer's -maxMB, read from the filer configuration at startup
 	// AllowUntrustedRemoteEndpoints lets a read of a remote-only object dial a
 	// mounted endpoint that resolves to a loopback / private / metadata host.
 	AllowUntrustedRemoteEndpoints bool
@@ -209,6 +214,7 @@ func NewS3ApiServerWithStore(router *mux.Router, option *S3ApiServerOption, expl
 		}
 		clientHost := option.advertisedHost()
 		masterClient = wdclient.NewMasterClient(option.GrpcDialOption, option.FilerGroup, cluster.S3Type, pb.ServerAddress(util.JoinHostPort(clientHost, option.GrpcPort)), option.DataCenter, "", *pb.NewServiceDiscoveryFromMap(masterMap))
+		masterClient.SetMetricsPort(option.MetricsPort)
 		// Build the object-write lock client and subscribe to the master's
 		// lock-ring updates BEFORE starting the master loop, so the initial
 		// LockRingUpdate sent on connect isn't dropped (the master only delivers