Skip network creation if network already exists in HNS (#1300)

* skip network creation if network already exists

* address comments

* address feedback

Author: aegal

network/hnswrapper/hnsv2wrapperfake.go

@@ -167,7 +167,7 @@ func (f Hnsv2wrapperFake) GetNetworkByName(networkName string) (*hcn.HostCompute
 	if network, ok := f.Cache.networks[networkName]; ok {
 		return network.GetHCNObj(), nil
 	}
-	return &hcn.HostComputeNetwork{}, nil
+	return nil, hcn.NetworkNotFoundError{}
 }
 
 func (f Hnsv2wrapperFake) GetNetworkByID(networkID string) (*hcn.HostComputeNetwork, error) {

network/network_windows.go

@@ -5,6 +5,7 @@ package network
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"strconv"
 	"strings"
@@ -310,14 +311,27 @@ func (nm *networkManager) newNetworkImplHnsV2(nwInfo *NetworkInfo, extIf *extern
 		return nil, err
 	}
 
-	// Create the HNS network.
-	log.Printf("[net] Creating hcn network: %+v", hcnNetwork)
-	hnsResponse, err := hnsv2.CreateNetwork(hcnNetwork)
+	// check if network exists, only create the network does not exist
+	hnsResponse, err := hnsv2.GetNetworkByName(hcnNetwork.Name)
+
 	if err != nil {
-		return nil, fmt.Errorf("Failed to create hcn network: %s due to error: %v", hcnNetwork.Name, err)
-	}
+		// if network not found, create the HNS network.
+		if errors.As(err, &hcn.NetworkNotFoundError{}) {
+			log.Printf("[net] Creating hcn network: %+v", hcnNetwork)
+			hnsResponse, err = hnsv2.CreateNetwork(hcnNetwork)
+
+			if err != nil {
+				return nil, fmt.Errorf("Failed to create hcn network: %s due to error: %v", hcnNetwork.Name, err)
+			}
 
-	log.Printf("[net] Successfully created hcn network with response: %+v", hnsResponse)
+			log.Printf("[net] Successfully created hcn network with response: %+v", hnsResponse)
+		} else {
+			// we can't validate if the network already exists, don't continue
+			return nil, fmt.Errorf("Failed to create hcn network: %s, failed to query for existing network with error: %v", hcnNetwork.Name, err)
+		}
+	} else {
+		log.Printf("[net] Network with name %s already exists", hcnNetwork.Name)
+	}
 
 	var vlanid int
 	opt, _ := nwInfo.Options[genericData].(map[string]interface{})

network/network_windows_test.go

@@ -11,6 +11,8 @@ import (
 	"testing"
 
 	"github.com/Azure/azure-container-networking/network/hnswrapper"
+
+	"github.com/Microsoft/hcsshim/hcn"
 )
 
 func TestNewAndDeleteNetworkImplHnsV2(t *testing.T) {
@@ -20,7 +22,7 @@ func TestNewAndDeleteNetworkImplHnsV2(t *testing.T) {
 
 	// this hnsv2 variable overwrites the package level variable in network
 	// we do this to avoid passing around os specific objects in platform agnostic code
-	hnsv2 = hnswrapper.Hnsv2wrapperFake{}
+	hnsv2 = hnswrapper.NewHnsv2wrapperFake()
 
 	nwInfo := &NetworkInfo{
 		Id:           "d3e97a83-ba4c-45d5-ba88-dc56757ece28",
@@ -47,3 +49,38 @@ func TestNewAndDeleteNetworkImplHnsV2(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestSuccesfulNetworkCreationWhenAlreadyExists(t *testing.T) {
+	nm := &networkManager{
+		ExternalInterfaces: map[string]*externalInterface{},
+	}
+
+	// this hnsv2 variable overwrites the package level variable in network
+	// we do this to avoid passing around os specific objects in platform agnostic code
+	hnsv2 = hnswrapper.NewHnsv2wrapperFake()
+
+	network := &hcn.HostComputeNetwork{
+		Name: "azure-vlan1-172-28-1-0_24",
+	}
+
+	_, err := hnsv2.CreateNetwork(network)
+
+	// network name is derived from network info id
+	nwInfo := &NetworkInfo{
+		Id:           "azure-vlan1-172-28-1-0_24",
+		MasterIfName: "eth0",
+		Mode:         "bridge",
+	}
+
+	extInterface := &externalInterface{
+		Name:    "eth0",
+		Subnets: []string{"subnet1", "subnet2"},
+	}
+
+	_, err = nm.newNetworkImplHnsV2(nwInfo, extInterface)
+
+	if err != nil {
+		fmt.Printf("+%v", err)
+		t.Fatal(err)
+	}
+}