Fix #7171: select instance network on which to assign floating ip

Add config parameter instance_floating_ip_net to control
floating ip assignment for a multi-homed instances.  This ensures
the floating ip can be correctly assigned to the instance port
that is connected to the preferred network for floating ip assignment.

This avoids the default first-returned selection method which may
choose a network to which floating ip's can't be assigned,
e.g. because that network is not reachable from the floating ip
network.

builder/openstack/builder.go

@@ -129,6 +129,7 @@ func (b *Builder) Run(ctx context.Context, ui packer.Ui, hook packer.Hook) (pack
 			FloatingIPNetwork: b.config.FloatingIPNetwork,
 			FloatingIP:        b.config.FloatingIP,
 			ReuseIPs:          b.config.ReuseIPs,
+			InstanceFloatingIPNet:      b.config.InstanceFloatingIPNet,
 		},
 		&communicator.StepConnect{
 			Config: &b.config.RunConfig.Comm,

builder/openstack/networks.go

@@ -2,6 +2,7 @@ package openstack
 
 import (
 	"fmt"
+	"log"
 
 	"github.com/google/uuid"
 	"github.com/gophercloud/gophercloud"
@@ -66,7 +67,10 @@ func FindFreeFloatingIP(client *gophercloud.ServiceClient) (*floatingips.Floatin
 // GetInstancePortID returns internal port of the instance that can be used for
 // the association of a floating IP.
 // It will return an ID of a first port if there are many.
-func GetInstancePortID(client *gophercloud.ServiceClient, id string) (string, error) {
+func GetInstancePortID(client *gophercloud.ServiceClient, id string, instance_float_net string) (string, error) {
+
+	selected_interface := 0
+
 	interfacesPage, err := attachinterfaces.List(client, id).AllPages()
 	if err != nil {
 		return "", err
@@ -79,7 +83,17 @@ func GetInstancePortID(client *gophercloud.ServiceClient, id string) (string, er
 		return "", fmt.Errorf("instance '%s' has no interfaces", id)
 	}
 
-	return interfaces[0].PortID, nil
+	for i := 0; i < len(interfaces); i++ {
+		log.Printf("Instance interface: %v: %+v\n", i, interfaces[i])
+		if interfaces[i].NetID == instance_float_net {
+			   log.Printf("Found preferred interface: %v\n", i)
+				 selected_interface = i
+				 log.Printf("Using interface value: %v", selected_interface)
+		}
+	}
+
+
+	return interfaces[selected_interface].PortID, nil
 }
 
 // CheckFloatingIPNetwork checks provided network reference and returns a valid

builder/openstack/run_config.go

@@ -28,6 +28,7 @@ type RunConfig struct {
 	ReuseIPs           bool              `mapstructure:"reuse_ips"`
 	SecurityGroups     []string          `mapstructure:"security_groups"`
 	Networks           []string          `mapstructure:"networks"`
+	InstanceFloatingIPNet       string            `mapstructure:"instance_floating_ip_net"`
 	Ports              []string          `mapstructure:"ports"`
 	UserData           string            `mapstructure:"user_data"`
 	UserDataFile       string            `mapstructure:"user_data_file"`

builder/openstack/step_allocate_ip.go

@@ -14,6 +14,7 @@ type StepAllocateIp struct {
 	FloatingIPNetwork string
 	FloatingIP        string
 	ReuseIPs          bool
+	InstanceFloatingIPNet			string
 }
 
 func (s *StepAllocateIp) Run(ctx context.Context, state multistep.StateBag) multistep.StepAction {
@@ -114,7 +115,7 @@ func (s *StepAllocateIp) Run(ctx context.Context, state multistep.StateBag) mult
 		ui.Say(fmt.Sprintf("Associating floating IP '%s' (%s) with instance port...",
 			instanceIP.ID, instanceIP.FloatingIP))
 
-		portID, err := GetInstancePortID(computeClient, server.ID)
+		portID, err := GetInstancePortID(computeClient, server.ID, s.InstanceFloatingIPNet)
 		if err != nil {
 			err := fmt.Errorf("Error getting interfaces of the instance '%s': %s", server.ID, err)
 			state.Put("error", err)