conf.ejs

global
  log         0.0.0.0           local2 info
  chroot      /var/lib/haproxy
  pidfile     /var/run/haproxy.pid
  daemon

defaults
  option      http-server-close
  option      http-pretend-keepalive
  timeout     connect           4s
  timeout     client            60s
  timeout     server            30s
  listen      stats             :50080
  mode        http
  stats       uri               /
  stats       auth              admin:admin

frontend    public            :80,:443
{{ for (var s in services) { }}
  {{ if (services[s].length && typeof services[s][0].frontend !== 'undefined') { }}
    {{ services[s][0].frontend.forEach(function (line) { }}
      {{- line }}
    {{ }) }}
  {{ } }}
{{ } }}

{{ for (var s in services) { }}
  # {{- s }}
  backend   {{- s }}
  stats     uri           /{{- s }}?stats
  stats     scope         .
  stats     hide-version
  stats     show-desc     {{- s }}
  stats     realm         {{- s }}
  {{ if (services[s][0]) { }}
  stats     show-desc     {{- s }}@{{- services[s][0].version }}
    {{ if (typeof services[s][0].backend !== 'undefined') { }}
      {{ services[s][0].backend.forEach(function (line) { }}
        {{- line }}
      {{ }) }}
    {{ } }}
  {{ } }}

  {{ services[s].forEach(function (srvc) { }}
    server {{- s }}-{{- srvc.port }} localhost:{{- srvc.port }} check
  {{ }) }}
{{ } }}

seaproxy.js

#!/usr/bin/env node

var seaport = require('seaport')
  , seaproxy = seaport.createServer({ host : 'localhost', port : 1026 })
  , fs = require('fs')
  , ejs = require('ejs')
  , configFile = __dirname + '/haproxy.conf'
  , exec = require('child_process').exec
  , spawn = require('child_process').spawn
  , changes = true
  , haproxy

ejs.open = '{{'
ejs.close = '}}'

seaproxy.on('allocate', reload)
seaproxy.on('assume', reload)
seaproxy.on('free', reload)

function reload () {
  changes = true
}

setInterval(function () {
  if (changes) {
    reloadHAProxy(function () {
      changes = false
    })
  }
}, 5000) // respond to changes every 5 seconds

seaproxy.listen(1026)

reloadHAProxy()

function reloadHAProxy (callback) {
  ejs.renderFile('./conf.ejs', { services : seaproxy.roles }, run)

  function run (error, haproxyConf) {
    fs.writeFile(configFile, haproxyConf, 'utf8', function () {
      var args = [ '-f', configFile, '-p', '/var/run/haproxy.pid' ]
      exec('cat /var/run/haproxy.pid', function (e, pid) {
        pid = pid.match(/[0-9]+/)
        if (pid && pid[0]) {
          console.info('haproxy already exists', pid[0])
          args.push('-sf')
          args.push(pid[0])
        }
        haproxy = spawn('/usr/sbin/haproxy', args)
        haproxy.stdout.pipe(process.stdout)
        haproxy.stderr.pipe(process.stderr)
        haproxy.on('exit', function (code, signal) {
          console.log('haproxy exit', code, signal)
        })
        return callback && callback()
      })
    })
  }
}
process.on('exit', function () { haproxy.kill() })

service-meta.json

{
  "web" : { 
    "title": "web",
    "role": "web@0.1.0",
    "frontend": [ 
      "acl web_acl path_dir -i web", 
      "acl web_acl hdr_beg(host) -i web", 
      "use_backend web if web_acl" 
    ],
    "backend": [
      "reqrep ^([^\\ :]*)\\ /web/(.*)     \\1\\ /\\2"
    ]
  }
}