lb.go

package main

import (
	"io"
	"log"
	"math/rand"
	"net"
	"time"
)

func main() {
	port := ":3632"
	log.Println("listening on", port)
	ln, err := net.Listen("tcp", port)
	if err != nil {
		log.Fatalln(err)
	}
	for {
		conn, err := ln.Accept()
		if err != nil {
			log.Println(err)
			continue
		}
		lb(getBackends)(conn)
	}
}

type backender func() []string

func getBackends() []string {
	backends := []string{
		":6011",
		":6012",
		":6013",
		":6014",
	}
	return backends
}

func lb(br backender) func(net.Conn) {
	return func(conn net.Conn) {
		var (
			be     = br()
			ep     = ""
			err    error
			remote net.Conn
		)
		if len(be) == 0 {
			log.Println("Error: backend list empty")
			return
		}
		{
			s := rand.NewSource(time.Now().UnixNano())
			r := rand.New(s) // initialize local pseudorandom generator
			idx := r.Intn(len(be))
			ep = be[idx]
		}
		log.Println(conn.RemoteAddr(), "<=>", ep)
		//
		remote, err = net.Dial("tcp", ep)
		if err != nil {
			log.Println(err)
			return
		}
		go func() {
			io.Copy(conn, remote)
		}()
		go func() {
			io.Copy(remote, conn)
		}()
	}
}