manager/deploy: do not allow deploying of empty topology (#994)

Co-authored-by: SIGSEGV <[email protected]>
Co-authored-by: Ti Prow Robot <[email protected]>

pkg/cluster/manager/deploy.go

@@ -87,6 +87,23 @@ func (m *Manager) Deploy(
 		return err
 	}
 
+	instCnt := 0
+	topo.IterInstance(func(inst spec.Instance) {
+		switch inst.ComponentName() {
+		// monitoring components are only useful when deployed with
+		// core components, we do not support deploying any bare
+		// monitoring system.
+		case spec.ComponentGrafana,
+			spec.ComponentPrometheus,
+			spec.ComponentAlertmanager:
+			return
+		}
+		instCnt++
+	})
+	if instCnt < 1 {
+		return fmt.Errorf("no valid instance found in the input topology, please check your config")
+	}
+
 	spec.ExpandRelativeDir(topo)
 
 	base := topo.BaseTopo()