RE: Transperant HTTP Redundancy.

> On 25-Mar-98 Javier Puche. CSIC RedIRIS wrote:
> > - Have both machines with IP addresses different than x.x.x.x but with
> > the ability to listen to x.x.x.x with a virtual interface when needed.
> > - When machine 1 attending x.x.x.x falls down, have the other machine
> > (2) detect that situation and set up a virtual interface for attending
> > x.x.x.x , do it also the other way around.
> > - Make sure that if either machine goes up again doesn't listen to IP
> > x.x.x.x before checking that the other machine is not doing that
> > already.
>
> Theres an url explaining that somewhere... but the problem is that this
kind
> of solution is not bulletproof.. imagine that for some reason the
> kernel panics
> with an harddisk failure.. sometimes when this happens the machine still
> replies to pings, squid is up and running, but obviously doesnt replies to
> requests.. so you could grab the ip address because the other machine is
still
> using it... or is there any way around this problem?
>

Sure, OSPF routing protocol via gated. If your machine crashes, it'll take
gated with it forcing it not to update via the HELLO protocol. So you take
two machines and configure a virtual interface on each machine to be 1.2.3.4
and advertise the route to your router. Set next-hop on your router to be
this IP and you should be in business.

If you want to load balance, set the OSPF weight equal to eachother, if you
just want a failover, set one a bit higher.

Alternatively, there's something called NAT (Network Address Translation)
which is a bit more intense. It can forward packets via load on servers and
technically speaking, the failover/load balancing servers don't need to be
on your LAN... they can be anywhere. The Linux version of this and some
general NAT information is over @ http://www.linas.org/linux/load.html.

Jordan

--
Jordan Mendelson     : http://jordy.wserv.com
Web Services, Inc.   : http://www.wserv.com