dnsdisco full example

db.dnsdisco.com

dnsdisco.com. 86400 IN SOA ns1.dnsdisco.com. adm.rafael.net.br. (
		2016022400	; serial
		86400		; refresh
		86400		; retry
		86400		; expire
		10 )		; minimum

dnsdisco.com. 86400 IN NS ns1.dnsdisco.com.

_test._tcp.dnsdisco.com. 10 IN SRV 1 10 7777 s1.dnsdisco.com.
_test._tcp.dnsdisco.com. 10 IN SRV 10 90 7777 s2.dnsdisco.com.
_test._tcp.dnsdisco.com. 10 IN SRV 2 30 7777 s3.dnsdisco.com.

s1.dnsdisco.com.  86400 IN A 192.168.122.80
s2.dnsdisco.com.  86400 IN A 192.168.122.125
s3.dnsdisco.com.  86400 IN A 192.168.122.199
ns1.dnsdisco.com. 86400 IN A 127.0.0.1

dnsdisco-client.go

package main

import (
	"bufio"
	"fmt"
	"io"
	"net"
	"strings"
	"time"

	"github.com/rafaeljusto/dnsdisco"
)

func main() {
	discovery := dnsdisco.NewDiscovery("test", "tcp", "dnsdisco.com")
	finish := discovery.RefreshAsync(5 * time.Second)

	defer func() {
		close(finish)
	}()

	for {
		if errs := discovery.Errors(); len(errs) > 0 {
			for _, err := range errs {
				fmt.Println(err)
			}
		}

		target, port := discovery.Choose()
		if target == "" || port == 0 {
			fmt.Println("No server selected")
			time.Sleep(time.Second)
			continue
		}

		conn, err := net.Dial("tcp", fmt.Sprintf("%s:%d", target, port))
		if err != nil {
			fmt.Println(err)
			time.Sleep(time.Second)
			continue
		}

		for {
			fmt.Fprintf(conn, time.Now().UTC().Format(time.RFC3339))

			message, err := bufio.NewReader(conn).ReadString('\n')
			if err != nil {
				if err != io.EOF {
					fmt.Println(err)
				}

				break
			}

			fmt.Println(strings.TrimSpace(message))
		}

		conn.Close()
		time.Sleep(time.Second)
	}
}

dnsdisco-server.go

package main

import (
	"flag"
	"fmt"
	"io"
	"net"
	"os"
	"sync/atomic"
)

var (
	name    = flag.String("name", "", "server name")
	counter uint64
)

func main() {
	flag.Parse()
	if name == nil {
		flag.PrintDefaults()
		os.Exit(1)
	}

	l, err := net.Listen("tcp", "0.0.0.0:7777")
	if err != nil {
		fmt.Println("Error listening:", err.Error())
		os.Exit(1)
	}
	defer l.Close()

	for {
		conn, err := l.Accept()
		if err != nil {
			fmt.Println("Error accepting: ", err.Error())
			os.Exit(1)
		}

		go handleRequest(conn)
	}
}

func handleRequest(conn net.Conn) {
	defer conn.Close()
	buf := make([]byte, 1024)

	reqLen, err := conn.Read(buf)
	if err != nil {
		if err != io.EOF {
			fmt.Println("Error reading:", err.Error())
		}
		return
	}

	atomic.AddUint64(&counter, 1)
	fmt.Printf("Received message: %s (%d)\n", string(buf[:reqLen]), counter)
	fmt.Fprintf(conn, "[%s] Message received: %s\n", *name, string(buf[:reqLen]))
}

The environment was created with 5 VMs (3 servers, 1 recursive/authoritative DNS and 1 client).