On Wed, 31 Mar 2004, David Nolan wrote:
Start by writing a stand alone script that can perform the change you need. I suggest using perl and Net::DNS::Update to send DDNS updates to your master.
the problem with the dns update method is that caches all around won't expire the "dead" address for too long of a time.
this is a better-behaved method if you have a small number of web servers all serving the same content on the same subnet:
1. each server has two ip addresses, one which is published in dns as an A record for "www.whatever.com", and the other is an "administrative" address. the published address is assigned to an alias interface, say eth0:1. the non-published address is not an alias.
2. when the web server boots, it ifup's the non-published address, but before configuring the published address on the alias interface it sends out a gratuitous arp for that address, and only configures it if it doesn't get a response (i.e. someone else isn't already using it). you can use "arping" to accomplish this:
http://www.gnu.org/directory/All_Packages_in_Directory/arping.html
if ! arping -q -D -c 5 -I eth0 ipaddr then # uh oh, some else is using that address on the subnet fi
You could also look at fake : http://www.vergenet.net/linux/fake/
It uses send_arp to prevent bad arp resolution if the failed server is still a bit alive (frozen but ping still ok, this happen frequently).
-- Fabien SALVI
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