Re: [cobalt-users] New IP Block - what the best way to add these

[Bruce <bruce@xxxxxxxxxxxxx>]

Hi,

Please see my theory(es) on this below

At 10:07 p.m. 21/08/2003 +1200, you wrote:
> Got an email from my provider yesterday that they are tidying up on IP 
> blocks and that they have now reassigned a block of new IP numbers to our 
> server (sigh) and we have to change over within a given time frame. I've 
> been searching most of the day to see what the best way to go about adding 
> these and changing over customers sites/DNS records without having any 
> downtime.

I see there has been quite a bit of debate on how/if this would work, heres 
some theoretical ideas on how to get it to work:

- Option 1 -
Since the Raq3 and Raq4's I work with allow a user to connect to any IP on 
the server, the only thing that is specific to the IP address is the 
webserver, all that should be required is to edit the httpd.conf file and 
add the new IP address for each site:
eg. on a line with
<VirtualHost 192.168.1.4>
replace it with:
<VirtualHost 192.168.1.4 192.168.1.3>
(assuming 192.168.1.4 is the old address and 192.168.1.3 is the new one)

You would probably need to add a dummy site to bring up an additional 
interface to handle the request.

This would cover all the sites being on two different IP addresses, and the 
old IP address could be removed after a reasonable time. The only main 
problem with it however it modifications in the GUI MAY replace these 
settings - however I have the above config on a Cube and changes in the GUI 
havnt effected it. (but Cubes are different)

As for the nameservers, you would need to edit the named.conf file and 
specify the two IP addresses (old and new)
Then play the waiting game for around 72 hours.

- Option 2 -
Probably not the best, but it could avoid playing with the httpd.conf file,
Add a new site which can respond on all the IP's (if need be add an extra 
site for each existing IP)
upload a script or util to look at the domain name and redirect to the IP 
address or preview link, or even just redirect requests to the real domain 
info (eg. runs a small web client which passes everything passed in back to 
the correct IP address for the domain)

Then move all the sites to their new IP address.

The nameservers could be setup with one of the old and one on the new (as 
mentioned) so that redundancy kicks in, with all zones pointing at the new 
IP addresses.

- End Options -

It is suggested that before attempting either of these options you drop the 
TTLs on the A records to as low as possible, so that the method you are 
using is not noticeable... those ISPs who don't obey the TTL (and hence 
should be shot) will just end up using the redirection method until they do 
drop the record.

Unfortunately when these things happen it is very difficult to avoid 
downtime, but I hope the ideas help out in someway,

--
Bruce
www.webfarm.co.nz
www.freeparking.co.nz