Adding check to prevent duplicate Network Container creation (#190)

* Adding check to prevent AzureNetworkContainer.exe from running if nc exists and the version has not changed.

* Making changes as per Tamilmani.

Author: jaer-tsun

cns/restserver/restserver.go

@@ -915,13 +915,22 @@ func (service *httpRestService) createOrUpdateNetworkContainer(w http.ResponseWr
 	switch r.Method {
 	case "POST":
 		if req.NetworkContainerType == cns.WebApps {
-			nc := service.networkContainer
-			if err := nc.Create(req); err != nil {
-				returnMessage = fmt.Sprintf("[Azure CNS] Error. CreateOrUpdateNetworkContainer failed %v", err.Error())
-				returnCode = UnexpectedError
-				break
+			// try to get the saved nc state if it exists
+			service.lock.Lock()
+			existing, ok := service.state.ContainerStatus[req.NetworkContainerid]
+			service.lock.Unlock()
+
+			// create/update nc only if it doesn't exist or it exists and the requested version is different from the saved version
+			if !ok || (ok && existing.VMVersion != req.Version) {
+				nc := service.networkContainer
+				if err = nc.Create(req); err != nil {
+					returnMessage = fmt.Sprintf("[Azure CNS] Error. CreateOrUpdateNetworkContainer failed %v", err.Error())
+					returnCode = UnexpectedError
+					break
+				}
 			}
 		}
+
 		returnCode, returnMessage = service.saveNetworkContainerGoalState(req)
 
 	default:
@@ -967,6 +976,9 @@ func (service *httpRestService) getNetworkContainerResponse(req cns.GetNetworkCo
 	var containerID string
 	var getNetworkContainerResponse cns.GetNetworkContainerResponse
 
+	service.lock.Lock()
+	defer service.lock.Unlock()
+
 	switch service.state.OrchestratorType {
 	case cns.Kubernetes:
 		var podInfo cns.KubernetesPodInfo
@@ -1049,7 +1061,11 @@ func (service *httpRestService) deleteNetworkContainer(w http.ResponseWriter, r
 		var containerStatus containerstatus
 		var ok bool
 
-		if containerStatus, ok = service.state.ContainerStatus[req.NetworkContainerid]; !ok {
+		service.lock.Lock()
+		containerStatus, ok = service.state.ContainerStatus[req.NetworkContainerid]
+		service.lock.Unlock()
+
+		if !ok {
 			log.Printf("Not able to retrieve network container details for this container id %v", req.NetworkContainerid)
 			break
 		}