allow service freeze/unfreeze on a setup (#13707)

an active running speedTest will reject all
new S3 requests to the server, until speedTest
is complete.

this is to ensure that speedTest results are
accurate and trusted.

Co-authored-by: Klaus Post <klauspost@gmail.com>

cmd/notification.go

@@ -1501,6 +1501,37 @@ func (sys *NotificationSys) GetClusterMetrics(ctx context.Context) chan Metric {
 	return ch
 }
 
+// ServiceFreeze freezes all S3 API calls when 'freeze' is true,
+// 'freeze' is 'false' would resume all S3 API calls again.
+// NOTE: once a tenant is frozen either two things needs to
+// happen before resuming normal operations.
+// - Server needs to be restarted 'mc admin service restart'
+// - 'freeze' should be set to 'false' for this call
+//   to resume normal operations.
+func (sys *NotificationSys) ServiceFreeze(ctx context.Context, freeze bool) []NotificationPeerErr {
+	serviceSig := serviceUnFreeze
+	if freeze {
+		serviceSig = serviceFreeze
+	}
+	ng := WithNPeers(len(sys.peerClients))
+	for idx, client := range sys.peerClients {
+		if client == nil {
+			continue
+		}
+		client := client
+		ng.Go(GlobalContext, func() error {
+			return client.SignalService(serviceSig)
+		}, idx, *client.host)
+	}
+	nerrs := ng.Wait()
+	if freeze {
+		freezeServices()
+	} else {
+		unfreezeServices()
+	}
+	return nerrs
+}
+
 // Speedtest run GET/PUT tests at input concurrency for requested object size,
 // optionally you can extend the tests longer with time.Duration.
 func (sys *NotificationSys) Speedtest(ctx context.Context, size int, concurrent int, duration time.Duration) []SpeedtestResult {