haproxy.conf

global
  log ${hosts:syslog}:${ports:syslog} local0
  maxconn  ${limits:open-files}

defaults
  mode http
  option httpclose
  option abortonclose
  retries 3
  option redispatch
  monitor-uri /_haproxy_ping_

  timeout connect 7s
  timeout queue   300s
  timeout client  300s
  timeout server  300s

  # Enable status page at this URL, on the port HAProxy is bound to
  listen stats  ${hosts:haproxy}:${ports:haproxy-stats}
  stats enable
  stats uri /
  stats refresh 5s
  stats realm Haproxy statistics

frontend loadbalancer
  bind ${hosts:haproxy}:${ports:haproxy}

  default_backend zope_default

# Backend for all nodes.
backend zope_default
  # Load balance based on number of connections
  cookie serverid insert nocache indirect
  balance roundrobin

  # Record where we've been
  rspadd X-Cluster:\ default

  server plone1 ${hosts:plone1}:${ports:plone1} cookie p${ports:plone1} check maxconn 3 rise 1 inter 10000 fastinter 2000
  server plone2 ${hosts:plone2}:${ports:plone2} cookie p${ports:plone2} check maxconn 3 rise 1 inter 10000 fastinter 2000