Products.cron4plone 1.1.7

1.1 Multiple instances

If you have multiple Zope instances in your buildout, it makes sense to add the zope-conf-additional to one instance only. This will ensure only one instance will try to run the @@cron-tick method.

Products.cron4plone should be present in all instances, or else the instance won’t have the software for CronTool object. This will cause errors on startup and you won’t be able to change the cron jobs.

1.2 Optionally use memcached server(s) to share locks

You would use memcached if your Zope instance runs on multiple machines. In this case, all machines would run @@cron-tick at the same time, which is not what you want, especially when creating content. Memcached will share a lock between multiple machine, so only one machine will run the cron job.

A memcached server is a standalone server process which you can either get via your favourite package manager (for Debian / Ubuntu: apt-get install memcached)

Install and configure memcached, and add unimr.memcachedlock to buildout.cfg:

[instance]
...
eggs =
    Products.cron4plone
    unimr.memcachedlock

You can specify where you are running your memcached servers in the MEMCACHEDLOCK_SERVERS environment variable, e.g.:

zope-conf-additional =
  <environment>
      MEMCACHEDLOCK_SERVERS <ip/hostname of host1>:<port>,<ip/hostname of host2>:<port>
  </environment>

The default port for memcached is 11211.

1.3 Optionally install memcached from buildout

You can also build memcached from a buildout:

parts +=
    memcached
    memcached-ctl
    supervisor

[memcached]
recipe = zc.recipe.cmmi
url = http://memcached.googlecode.com/files/memcached-1.4.0.tar.gz
extra_options = --with-libevent=${libevent:location}

[memcached-ctl]
recipe = ore.recipe.fs:mkfile
path = ${buildout:bin-directory}/memcached
mode = 0755
content =
 #!/bin/sh
 PIDFILE=${memcached:location}/memcached.pid
    case "$1" in
      start)
       ${memcached:location}/bin/memcached -d -P $PIDFILE
        ;;
      stop)
        kill `cat $PIDFILE`
        ;;
      restart|force-reload)
        $0 stop
        sleep 1
        $0 start
        ;;
      *)
        echo "Usage: $SCRIPTNAME {start|stop|restart}" >&2
        exit 1
        ;;
    esac

You need to have the libevent development libraries (apt-get install libevent-dev) or in buildout:

[libevent]
recipe = zc.recipe.cmmi
url = http://www.monkey.org/~provos/libevent-1.3b.tar.gz

Make sure that the libevent.so (shared object) file is in your LD_LIBRARY_PATH before you start the memcached server if you build the libevent library from the buildout.

If you use supervisor, you can add a line like this to start the memcached server:

10 memcached ${buildout:directory}/parts/memcached/bin/memcached