Jan 22, 2006

first of all sorry for my bad english writing its not my first language.

We have few servers and all of them runs Cpanel/WHM, We have more then 1000+ differents account with dedicated IP

We need to renumbering all of these account with a minimum pf downtime ... We are not moving our servers to a new location we only need to change the accounts IP.

The old IP can continue to resolve on our server for few weeks

For a minimum of downtime we proceed like that for our renumbering needs :

- Change site IP from WHM to
- We edit httpd.conf :

it work really great ..... but it will take an eternity for 1000+ accounts.

We can also with the Firewall forward the old IP to the new one ... but the job will be in my mind very hard and long to do ... more then the previous option.

I'm curious to know if someone here have a better solution of idea to do mass renumbering without downtime.




Jun 24, 2005
Actually changing an IP doesn't cause any downtime whatsoever
in and of itself and can be changed either from WHM, from the shell
using easy "replace" commands, or manually editing apache, cpanel,
and DNS zone files. The method used really doesn't matter though.

What "APPEARS" to be downtime when you change a site's IP address
is actually in reality the delay time it takes for all the ISPs in the world
and the user computer's out there around the world to update their
locally cached DNS zone information.

Those who have never before visited a site that you have recently changed
the IP address will probably have no trouble connecting to the site immediately
at the new IP address. However, those who recently or regularly connect to
those same sites will think they are down because what is really happening is
that their computers remember the old original IP address and trying to connect
to that IP location instead of the new IP address which may actually already
be live in the DNS zones and replicated worldwide but has not pulled down due
to local DNS caching in their own computers or at their ISPs (common).

If you want seamless IP changes as possible:

Setup the server to accept BOTH ip addresses for the accounts
and overlap those IPs on Apache during the DNS update period.

Reduce the TTL for the DNS zones and updates so that the DNS zones
are cached less and updated quicker worldwide temporarily while the
change is in progress and then go ahead and update the DNS IP resolution.
(NOTE: The DNS should only have the new IP address only during this period)

In a couple of days time, drop Apache accepting the original IP address
and change the accounts to operate on the new IP address only.

That's about the most seamless way to do it. If anyone still has problems
connecting, it's likely their local ISP is deeply caching DNS information and
they could override this problem by placing a line in the "hosts" file on their
own computer with their web address and the new IP address.
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