[nzlug] Webserver - Automatic Failover

[Liam Farr]

Hi,
I had a similar solution suggested to me (by the linux engineer I normally
use), combined with say a TTL value of 1-5 minutes. He said there were other
(more complex) ways to do it but what you have suggested was the easiest.

I would be nice if the user didn't have to restart their browser, (as most
users will be technically un-enlightened (windows), and probably wont
initially try restarting).

But some redundancy in the event of an outage is better than none,
especially when 50% of business revenue comes via the web portal.

-- 
Kind Regards

Liam Farr

Director
Farr Networks Limited
Ph: +64 27 6664644
Em: liam at farr.net.nz
Web: www.farr.net.nz

On 27/06/07, Jim Cheetham <jim at gonzul.net> wrote:
>
> On 27/06/07, Liam Farr <liam at farr.net.nz> wrote:
> >
> > Location 1
> > Primary DNS (Centos Based, BIND9)
> > Web server (Apple OSX, apache, mysql, php)
> > Location 2
> > Secondary DNS (Any os, server to be built)
> > Web server (Any os, server to be built, apache, mysql, php)
>
>
> Inherently both DNS and email are pretty much fail-over-able out of the
> box.
> However it's arguable that email doesn't need to be redundant at all, as a
> short outage (in the order of ~<24 hours) will pretty much automatically
> recover automatically. You don't need an independant machine just for DNS,
> it's low-load and should be on the other service machine.
>
> The web server is more interesting, however. Unless your two application
> back-ends are aware of each other, you will have session/cookie affinity
> with only one server at a time. There will not be an effective way of
> moving
> a user session from one server to another, should one go down.
>
> I recently saw a nice trick for cheap redundancy, which assumes you're
> protecting only against an outage of a site or server, as opposed to "just
> apache". Have two master DNSs on the two machines, with slightly different
> zone data - machine 1's DNS says that machine 1 is the webserver; machine
> 2's DNS says that machine 2 is the webserver. Declare any of the machines
> as
> the primary DNS - say number 1. When machine 1 goes off the air, you lose
> all the current user sessions (until they restart their browsers) ... but
> any new request for DNS will automatically retry onto machine 2 ... and be
> told that the webserver is on machine 2.
>
> This will scale up to 3 or 4 machines ... it's unusual to have more than 4
> DNS servers named in the registry, but not impossible for some.
>
> You're bound to have more questions ... :-)
>
> -jim
> _______________________________________________
> NZLUG mailing list NZLUG at linux.net.nz
> http://www.linux.net.nz/cgi-bin/mailman/listinfo/nzlug