add-delete-alias-ip.go

// Adds, then removes an alias IP from a VM
package main

import (
	"context"
	"flag"
	"fmt"
	"log"
	"os"
	"time"

	"github.com/kr/pretty"
	"google.golang.org/api/compute/v1"
)

var (
	project      = flag.String("project", "", "project id")
	zone         = flag.String("zone", "", "zone (required)")
	subnet_range = flag.String("range", "", "subnet range to add and remove alias from")
)

func main() {
	flag.Parse()

	if flag.NArg() != 2 {
		log.Fatalf("Usage: %s [-p project] [-z zone] INSTANCE ALIAS_IP", os.Args[0])
	}

	instance := flag.Arg(0)
	alias := flag.Arg(1)

	if *project == "" || *zone == "" || *subnet_range == "" {
		log.Fatal("--project and --zone and --range are required")
	}

	ctx := context.Background()

	computeService, err := compute.NewService(ctx)
	if err != nil {
		log.Fatalf("could not init compute: %s", err)
	}

	err = addAlias(computeService, *project, *zone, instance, *subnet_range, alias)
	if err != nil {
		log.Fatal(err)
	}
	// NOTE: in real code you'd want to wait for the previous op to complete
	time.Sleep(time.Second * 10)
	err = removeAlias(computeService, *project, *zone, instance, alias)
	if err != nil {
		log.Fatal(err)
	}
}

func addAlias(gce *compute.Service, project, zone, instance_name, subnet_range, alias_ip string) error {
	svc := compute.NewInstancesService(gce)

	instance, err := svc.Get(project, zone, instance_name).Do()
	if err != nil {
		return err
	}

	var new_interface compute.NetworkInterface
	old_interface := instance.NetworkInterfaces[0]

	new_interface.AliasIpRanges = old_interface.AliasIpRanges
	new_interface.AliasIpRanges = append(new_interface.AliasIpRanges, &compute.AliasIpRange{
		IpCidrRange:         alias_ip,
		SubnetworkRangeName: subnet_range,
	})
	new_interface.Fingerprint = old_interface.Fingerprint
	pretty.Println("old", old_interface)
	pretty.Println("new", new_interface)

	op, err := svc.UpdateNetworkInterface(project, zone, instance_name, "nic0", &new_interface).Do()
	if err != nil {
		return err
	}

	fmt.Println("add alias op: ", op.Name)
	return nil
}

func removeAlias(gce *compute.Service, project, zone, instance_name, alias_ip string) error {
	svc := compute.NewInstancesService(gce)

	// To remove an alias we have to overwrite the interface's alias IP list, so we need
	// the existing instance.
	instance, err := svc.Get(project, zone, instance_name).Do()
	if err != nil {
		return err
	}

	var new_interface compute.NetworkInterface

	old_interface := instance.NetworkInterfaces[0]
	for _, r := range old_interface.AliasIpRanges {
		if r.IpCidrRange != alias_ip {
			new_interface.AliasIpRanges = append(new_interface.AliasIpRanges, r)
		}
	}

	new_interface.Fingerprint = old_interface.Fingerprint
	pretty.Println("old", old_interface)
	pretty.Println("new", new_interface)

	op, err := svc.UpdateNetworkInterface(project, zone, instance_name, "nic0", &new_interface).Do()
	if err != nil {
		return err
	}

	fmt.Println("delete alias op", op.Name)
	return nil
}