Shared cron jobs

[Ben Hollingsworth]

Neil wrote:
> you have a virtual ip which only one of the hosts has at a time. I'd use that
>
> have the cron job on both but making it check if its host has that ip address and exit if it doesn't.
>   

That's essentially the same mechanism I use to handle failover on a pair 
of AIX boxes at work.  In that case, all our application data is on a 
shared SAN that both servers can mount, but only one at a time (by the 
live system).  In my cron jobs, I do something like:

00 01 * * * if [ -f /file/on/shared/filesystem ]; then /command/to/run; fi

so that /command/to/run will only get executed if 
/file/on/shared/filesystem exists.  It works quite well.  You could 
replace that conditional with something that checks for the existence of 
your VIP interface, or anything else that is guaranteed to only exist on 
the live box.  The command being run doesn't have to know anything about 
what's happening, since the failover check is being done within cron.

> Dan Brown wrote:
>   
>> My pair of LVS servers share the same database.  I have a couple of sites
>> which import data daily from other sites, or via uploaded files.  I do not
>> want the servers to both be running the same job at the same time obviously
>> so I'd like to swap out crontab files when the backup director takes over.
>>