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.
PyBal is currently installed on our LVS hosts, in directory /usr/sbin. Start or stop it by
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.:
[text] protocol = tcp ip = 18.104.22.168 port = 80 scheduler = wlc config = file:///etc/pybal/text-squids [images] protocol = tcp ip = 22.214.171.124 port = 80 scheduler = wlc config = file:///etc/pybal/upload-squids
Beware, the code as checked out from git 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 command line option, but for now edit that file to DryRun = False.
The configuration files are generated via puppet.
- lvsmon: The predecessor to PyBal