[cups.general] CUPS in HA configurations

[Michael Sweet]

cupsd is not designed to use a shared configuration or spool directory, and "Bad Things (tm)" will happen if you do so.

Sharing /usr/share/cups is fine, of course, but don't expect /etc/cups or /var/*/cups to be safe.

On Dec 16, 2010, at 6:07 PM, Jason Czerak wrote:

> I'm configuring an HA pair on 1.3.7 on RHEL 5.3. I'll be doing an upgrade on things to RHEL 5.5 in the spring. I have a few questions that you folks may be quick to answer before I waste paper and time. :)
> 
> I'm experimenting with placing /etc/cups on an NFS mount (netapp). So far the HA pair work well. if you fail the server or pause the queues print jobs work as expected.
> 
> /var/spool/cups and /var/cache/cups are local to each node at this time.  I'm curious if I can share these locations as well? the job ID file is the first hurdle. If I do share /var/cache/cups I'll ensure it's mounted with actimeo=0. I'm curious if I'm to expect a race or locking condition if both nodes in the HA pair try to update this file with the next ID?
> 
> The idea here is to save the spooled data. I may have a requirement that I keep printed data for a period of time so if a reprint is needed the spooler can take care of that. This way I can have one spot for the data, not two
> 
> /var/cache/ppds.dat. I've noticed that the second node doesn't have this file and is working well. I have yet to add a printer while both are sharing the /etc/cups data. What issues might I expect with this data file out of sync?
> 
> The main idea here with sharing /etc/cups is maintenance of the queue's. I'm going to end up with near 100. I'd like to ensure both servers are identical so there's not oddities.
> 
> Second big question is what happens to a large print job that the cups server fails mid spool? If client "C" is spooling to server "A" and server "A" disappears (crashes, hardwareissue, network issue, etc) mid spool will client "C" restart the spool to server "B"? or fail?
> 
> 
> 
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________________________________________________________________________
Michael Sweet, Senior Printing System Engineer, PWG Chair