Check if there is an interface with a given name

ec2_dns_check.go

package main

import (
	"log"
	"net"
	"strings"
)

func trace(fmt string, args ...interface{}) {
	log.Printf(fmt, args...)
}

func HasAddrWithName(name string) (bool, error) {
	ifaces, err := net.Interfaces()
	if err != nil {
		return false, err
	}
	for _, iface := range ifaces {
		addrs, err := iface.Addrs()
		if err != nil {
			trace("%s", err)
			continue
		}
		for _, addr := range addrs {
			ipaddr, _, err := net.ParseCIDR(addr.String())
			if err != nil {
				trace("%s", err)
				continue
			}
			hosts, err := net.LookupAddr(ipaddr.String())
			if err != nil {
				trace("%s", err)
				continue
			}
			for idx, h := range hosts {
				trace("%d: %s\n", idx, h)
				if strings.Contains(h, name) {
					return true, nil
				}
			}
		}
	}
	return false, nil
}

func main() {
	hasAddr, err := HasAddrWithName(".ec2.internal")
	if err != nil {
		log.Fatal(err)
	}
	if hasAddr {
		log.Println("inside ec2")
		return
	}

	log.Println("Not inside ec2")
}