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PyBal is a LVS monitoring script. It's written in Python using the Twisted framework.

For more information about Wikimedia's LVS setup in general, see LVS.

At this moment, just a few features distinguish it from lvsmon:

  • It's using asynchronous communication, and thus runs all checks in parallel instead of sequentially
  • It has an extra monitoring method called IdleConnection, which keeps an idle connection open to all squids, and therefore notices immediately when the Squid processes are shut down / crashing
  • It can fetch server lists over HTTP as well as from the local filesystems

...but I intend to polish it more, and extend it with useful things.

The script is in Wikimedia's Git repo "operations/debs", subdirectory pybal.

-- Mark


PyBal is currently installed on our LVS hosts, in directory /usr/sbin. Start or stop it by

 /etc/init.d/pybal start|stop

Configuration is in /etc/pybal/. pybal.conf defines the LVS service parameters

The list of pooled hosts resides wherever the pybal::web class is installed via puppet, under the directory /srv/pybal-config and it will be reachable via the internal address http://configuration-master.$site.wmnet/pybal, with one file per LVS service. Attributes:

  • weight: a larger number means that more requests get sent to this server in comparison with others
  • enabled: either True or False, depending on whether you want requests to be sent to this server

The format should be fairly self explanatory; the files more or less use Python assignment / dictionary syntax.

PyBal supports multiple LVS services through a single instance and configuration file pybal.conf, e.g.:

protocol = tcp
ip =
port = 80
scheduler = wlc
config = file:///etc/pybal/text-squids

protocol = tcp
ip =
port = 80
scheduler = wlc
config = file:///etc/pybal/upload-squids

Beware, the code as checked out from git has DryRun = True set in, meaning that it will not modify any actual IPVS state but only show the commands for debugging. This should be changed to a command line option, but for now edit that file to DryRun = False.

The configuration files are generated via puppet.

How to

See LVS.

See also

  • lvsmon: The predecessor to PyBal