[CentOS] *tangent* High Availability using 2 sites -- yep, "propogation."

Thu Jan 5 23:20:46 UTC 2006
Les Mikesell <lesmikesell at gmail.com>

On Thu, 2006-01-05 at 16:58, Mickael Maddison wrote:
> Hello Les,
> Thanks for that info.  I'm playing with this now and although the
> 'failover' process seems rather slow, it does seem to be doing what I
> need. I setup a subdomain entry to point to 4 IP's, only one if which
> is actually working, and indeed, when IE get's a non-active IP, it
> eventually goes to the next one until it finally finds the actual live
> IP.  Once it gets the live one, the site works as expected (of
> course).
> I'm glad I stumbled onto this thread... for my client's current need,
> this will do the trick nicely.

If you are getting the standard ICMP responses for failure it
should find the working address pretty quickly. You can test
that by (from a linux box):
telnet ip_address 80
You should get a 'connection refused' error quickly on a target
that is up but does not have a web server running, or a 'no route
to host' if the machine is completely down at that address.  If
you just have a long delay waiting for the connection you have
a firewall dropping the ICMPs - which may or may not be under
your control.

If you know a location is going to be down it will help to
remove that address from DNS but as the other comments in this
thread point out, you can't count on the changes to reach the
app quickly.

  Les Mikesell
   lesmikesell at gmail.com