App Container discovery via DNS TXT record

main.go

package main

import (
	"fmt"
	"github.com/miekg/dns"
	"log"
	"net"
	"os"
	"strings"
)

type AcDiscovery struct {
	Prefix string
	UrlTmpl string
}

func main() {
	config, _ := dns.ClientConfigFromFile("/etc/resolv.conf")
	c := new(dns.Client)

	m := new(dns.Msg)
	m.SetQuestion(dns.Fqdn("_ac-discovery.example.com"), dns.TypeTXT)
	m.RecursionDesired = true

	r, _, err := c.Exchange(m, net.JoinHostPort(config.Servers[0], config.Port))
	if r == nil {
		log.Fatalf("error: %s\n", err.Error())
	}

	if r.Rcode != dns.RcodeSuccess {
		log.Fatalf(" Invalid record returned")
	}

	for _, a := range r.Answer {

		if t, ok := a.(*dns.TXT); ok {
			log.Println(t.Txt)
			
			sp := strings.Split(t.Txt[0], " ")
			fmt.Printf("%#v\n", sp)
			
			discovery := AcDiscovery{}

			for _, s := range sp {
				kv := strings.Split(s, "=")
				
				if kv[0] == "prefix" {
					discovery.Prefix = kv[1]
				}

				if kv[0] == "url-tmpl" {
					discovery.UrlTmpl = kv[1]
				}
			}

			fmt.Printf("%#v\n", discovery)
		}

	}
}