Dynamic haproxy backends with buildout

buildout.cfg

[buildout]
backends = 4


parts = 
    myapp
    client
    haproxy-build
    haproxy-config
    supervisor

[myapp]
recipe = zc.recipe.egg
eggs =
    Paste
    PasteScript
    PasteDeploy
    myapp

[client]
recipe = z3c.recipe.paster:serve
eggs = ${myapp:eggs}
ini =
    [app:myapp]
    use = egg:myapp
    
    [server:main]
    use = egg:gunicorn#main
    host = 127.0.0.1
    port = %(http_port)s
    
    [DEFAULT]
    # set the name of the zope.conf file
    zope_conf = ${buildout:parts-directory}/${:_buildout_section_name_}/zope.conf

zope.conf =
    <zodb main>
      cache-size 5000
    
      <zeoclient>
        blob-dir ${buildout:directory}/var/blobstorage-${:_buildout_section_name_}
        cache-size 128MB
        name zeostorage
        server 127.0.0.1:8100
        shared-blob-dir off
        storage 1
      </zeoclient>
    </zodb>
    
    <eventlog>
      <logfile>
        formatter zope.exceptions.log.Formatter
        path ${buildout:directory}/var/log/${:_buildout_section_name_}.log
      </logfile>
      <logfile>
        formatter zope.exceptions.log.Formatter
        path STDOUT
      </logfile>
    </eventlog>

[haproxy-build]
recipe = plone.recipe.haproxy
url = http://haproxy.1wt.eu/download/1.4/src/haproxy-1.4.15.tar.gz
target = linux26

[haproxy-conf]
recipe = collective.recipe.template[genshi]:genshi
input = ${buildout:directory}/templates/haproxy.conf.in
output = ${buildout:directory}/etc/haproxy.conf
frontend-host = 127.0.0.1
frontend-port = 8000
backends = ${buildout:backends}
base_port = 8080

[supervisor]
recipe = collective.recipe.supervisor
programs =
    10 client-%(process_num)01d (numprocs=4) ${buildout:directory}/bin/client [http_port=808%(process_num)01d] ${buildout:directory} true

client.ini

[app:myapp]
use = egg:myapp

[server:main]
use = egg:gunicorn#main
host = 127.0.0.1
port = %(http_port)s

[DEFAULT]
# set the name of the zope.conf file
zope_conf = /home/user/app/parts/client/zope.conf

haproxy.conf

global
  ...

defaults
  ...

frontend zeocluster
  bind 127.0.0.1:8000
  default_backend zope

backend zope
  appsession __ac len 32 timeout 1d
  balance leastconn
  cookie sid insert nocache indirect
  option httpchk GET /

  server client0 127.0.0.1:8080 cookie p0 check maxconn 1 rise 1
  server client1 127.0.0.1:8081 cookie p1 check maxconn 1 rise 1
  server client2 127.0.0.1:8082 cookie p2 check maxconn 1 rise 1
  server client3 127.0.0.1:8083 cookie p3 check maxconn 1 rise 1

haproxy.conf.in

global
  ...

defaults
  ...

frontend zeocluster
  bind ${options['frontend-host']}:${options['frontend-port']}
  default_backend zope

backend zope
  appsession __ac len 32 timeout 1d
  balance leastconn
  cookie sid insert nocache indirect
  option httpchk GET /
{% for i in range(0, int(options.get('backends', '0'))) %}
  {% python
    port = int(options.get('base_port', '8080')) + i
  %}
  server client${i} 127.0.0.1:${port} cookie p${i} check maxconn 1 rise 1
{% end %}

supervisor.conf

[supervisord]
childlogdir = /home/user/app/var/log
logfile = /home/user/app/var/log/supervisord.log
logfile_maxbytes = 50MB
logfile_backups = 10
loglevel = info
pidfile = /home/user/app/var/supervisord.pid
umask = 022
nodaemon = false
nocleanup = false

[program:client-%(process_num)01d]
command = /home/user/app/bin/client http_port=808%(process_num)01d
process_name = client-%(process_num)01d
directory = /home/user/app
priority = 10
redirect_stderr = true
numprocs = 4

zope.conf

site-definition /home/user/app/parts/client/site.zcml

<zodb main>
  cache-size 5000

  <zeoclient>
    blob-dir /home/user/app/var/blobstorage-client
    cache-size 128MB
    name zeostorage
    server 127.0.0.1:8100
    shared-blob-dir off
    storage 1
  </zeoclient>
</zodb>

<eventlog>
  <logfile>
    formatter zope.exceptions.log.Formatter
    path /home/user/app/var/log/client.log
  </logfile>
  <logfile>
    formatter zope.exceptions.log.Formatter
    path STDOUT
  </logfile>
</eventlog>