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Re: Mirror applications on Linux Server

 On 28/09/10 14:05, Miles Fidelman wrote:
lrhorer wrote:
If there is a better forum for this, let me know and I will post my
questions there.

I am building an application which needs to have high reliability.  I
have two essentially identical Linux servers which can host the
application.  Right now, I have the programs - a bash script and a c
binary, running on one machine every minute in a cron job.  I also have
an rsync cron job running to synchronize the files on the standby
machine so the data (and binaries, of course) will be identical.  What
I need to do is have the standby machine take over operations if the
applications on the primary machine quite working, for whatever reason.
Of course I can easily ping the primary to make sure the machine is up,
but what is going to be my best bet for having the standby machine wake
up and start running the apps every minute until such time as the
primary comes back online?  I'm wide open on how to implement.  An
external application would be great, or I could write either or both c
or shell apps to have the two machines talk to one another.
It may be overkill, but take a look at Pacemaker and the Linux-HA Project - http://www.linux-ha.org - it's specifically intended for such applications.

Also look at DRBD - www.drbd.org - which mirrors a disk (or partition), in realtime across two machines.

The combination gives you automated fail-over capability.

Now, if you want to get really fancy, you can run your application in a virtual machine, and use pacemaker and DRBD to fail-over the entire VM.

Be warned, it takes a while to get all of these working properly - both individually and in combination. You could also take a look at ganeti - http://code.google.com/p/ganeti/ - which pulls a bunch of the pieces together.

DRBD and soforth might be overkill, or it might not. If you think it is and are happy with the rsync you can stick to that and use heartbeat to monitor the application. Easy to setup as well

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