[TriLUG] clustering or server mirroring

[David McDowell]

It would seem to further what I am looking for, High Availability over
load balance... I'm not running a gazillion hit a day site, but more
of one that just needs to not go down.  This setup will be between 2
slots in the same rack on gigabit eth.  Yes, if the T1 goes, so goes
the site.  The website won't be storage intensive, though it will be
interacting with a DB.  To have a 2nd DB box might be the difficult
purchase to make, however, a 2nd web box won't hurt to badly.  Yes, if
the DB goes, so goes the site.  Shared storage?  Like an external SAN
(if I have my technology right)??

Also, if you have Load Balance vs High Availability, if one of your
boxes dies, as long as one can handle the current load, haven't you
also accomplished your goal?  I am thinking that if I change
httpd.conf on box A, that I would want that change replicated to box B
immediately.

Thanks,
David McD

*goes back to reading that article posted earlier in thread*


On 4/19/05, John Berninger <johnw at berningeronline.net> wrote:
> On Tue, 19 Apr 2005, David McDowell wrote:
> 
> > One in the same?  Here's my idea.  I'd like to use CentOS 4 if
> > possible to do this.  I would like to have my webserver mirrored on
> > another machine so that if one goes down, the site continues to run.
> > If I change a config on one machine, the config should change on the
> > mirrored machine.  Is this running a cluster or is this some other
> > kind of setup?  Basically I have some time at work to play.  Any good
> > resources for this kind of information?  Basically I want 2 servers to
> > be identical mirrors of one another so that if one of the 2 goes down,
> > I'm still online.  And, if I repair the broken one, it can resync
> > itself so that the mirror of the 2 machines is identical again.
> > Suggestions, links, etc?
> 
>        The same, but not.
> 
>        Take the following with a grain of salt, as I'm coming from the
> standpoint of "CentOS is a rebuilt RHEL, RHEL has packages to do this,
> why not pay up for it" despite knowing that's not gonna happen.
> 
>        There are two types of clustering that I know of - high
> availability and load balancing.  HA gets you fault tolerance, LB gets
> you greater throughput with a little bit of fault tolerance.
> 
>        What you describe could be either - if you just need the data
> replicated, and the actual httpd.conf won't change, LB would be easier.
> set up a "shared" repo for the data, point both web servers at it for a
> DocumentRoot, of off you go.  If the httpd.conf will change, LB is still
> possible, but more of a PITA, and then HA becomes easier.
> 
>        Either way, doing it "right" involves a lot of extra stuff that
> you probably won't be able to convince your boss to pony up for - like
> true shared storage, multiple machines, etc.
> 
>        Are you wanting to have tolerance between remove sites, or
> between slots in a rack?
> 
> --
> John Berninger
> 
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