Re: Backup mirror machine

[Bill Moseley <moseley@hank.org>]

On Thu, May 05, 2005 at 03:30:46PM -0700, Alvin Oga wrote:
> one script ... change-me-from-slave-to-master.sh   and symlinked to "N"

But that system turns out to be harder to keep in sync.

> > What I'd like to do, I think, is have a system that ran as a separate
> > machine, but I could reboot and at the LILO prompt select another
> > configuration that makes it boot with the other machines IPs and
> > config settings.
> 
> you cannot tell lilo to boot a remote machine

No, I'm not asking that.  I was thinking I could use lilo to boot a
different configuration.  I suppose I could use the init scripts to
setup symlinks for /etc/network/interfaces and for all the services I
run.  That's basically what I have now -- but I've found it hard to
manage.

So, I was thinking more of a system that uses rsync to keep a copy of
the files that make "master" what it is (a machine with specific IPs,
and a collection of services configured a specific way, and data) on
the "slave" machine.  And then have a way to reboot the slave machine
and have it start using the backup data making it act as the master.

   if ( running_as("slave") )
        ln -s /slave.etc /etc
        ln -s /slave.var /var
        [...]
    else
        ln -s /master.etc /etc
        ln -s /master.var /var
        [...]

Or maybe mount the dirs instead.

Considering /etc/fstab is needed at boot, it's not that easy to place
/etc on a separate partiton (initrd would be one solution, I
suppose), or to symlink late in the boot process.

Perhaps dual-boot would be a good way to go.  Boot normally in "slave"
mode and mount partition(s) under /backup and rsync from the master
machine to the slave's /backup/etc, /backup/var, etc. dirs.

Then when there's a failure in master, power down master, and reboot
the slave machine into "master" mode which then mounts that partition
or partitions at /etc, /var, etc.

But, I still don't see that working since the backup of master onto
slave will contain hardware dependent settings that don't work on
slave -- like /etc/fstab.  I'm not sure what else (/etc/modules,
perhaps).

I often wonder why there's not two /etc directories -- one for
machine specific settings and another for application settings that
don't really depend on a specific hardware configuration.


> > Any Suggestions?
> 
> gazillion ways to do it

Thanks, but I was only looking for one or two.

-- 
Bill Moseley
moseley@hank.org