[CentOS] High Availability using 2 sites

[Bryan J. Smith]

Tim Edwards <tim at registriesltd.com.au> wrote:
> We currently have a backup site at a different location to
> our main site. This backup site mirrors (as closely as
> possible) our main services, particularly web serving.
> Is there a way to have the backup site act as a failover
> for the main site using something like Linux-HA? 
> They are on seperate internet connections with different IP
> ranges.

Yes and no.

Yes in that you have a couple of options -- one common, one
pretty much a hack.

The common one is to have your own autonomous system number
and run BGP.  That way you control your IP assignments,
failover, etc... in ways that are efficient and quickly
propogated.

The hack is to put routers and/or 1-to-1 NAT devices at each
site, which can redirect traffic to the other site.  That is
less efficient and can cause some headaches.

No in the fact that there's really no "software" or "service"
facility to deal with this.  Round robin DNS does nothing to
solve this.  Name propogation is always an issue.

So it's something you can only address at the IP-level --
either by having your own, Internet-recognized autonomous
system number, or redirecting IPs from each site to the other
when servers/sites go down.

-- 
Bryan J. Smith     Professional, Technical Annoyance                      b.j.smith at ieee.org      http://thebs413.blogspot.com
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*** Speed doesn't kill, difference in speed does ***