PyBal

Revision as of 09:09, 11 September 2012

PyBal is a LVS monitoring script quite similar to lvsmon. 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 MediaWiki CVS SVN repo mediawiki, subdirectory pybal.

-- Mark

Setup

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

 /etc/init.d/pybal start|stop

NOTE that recently pybal seems to not always stop when receiving a TERM signal (i.e. via this script). So you need to check the process start time and see if it *really* restarted, if not kill -9 manually, then start via script.

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

The list of pooled hosts resides in /home/w/conf/pybal (on fenari), 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, depnding 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.:

[text]
protocol = tcp
ip = 145.97.39.155
port = 80
scheduler = wlc
config = file:///etc/pybal/text-squids

[images]
protocol = tcp
ip = 145.97.39.156
port = 80
scheduler = wlc
config = file:///etc/pybal/upload-squids

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

The configuration files are (manually) backed up in /home/wikipedia/conf/pybal.

Howto

See LVS.