IP assignment for virtual webhosting (how to move namebased virt host)

At 21:29 9-05-00 -0400, Brian Dickson wrote:
>The issue with non-IP based virtuals, is the difficulty and complexity, and
>more important, time-sensitivity involved, in *relocating* between servers.
>DNS-based virtuals are impacted by caching resolvers, which are ubiquitous.
>Lowering timers has risk too, especially if load spikes occur, eg for longer
>than timer values.
>
>If everyone is aware of the "slashdot" effect, then you can appreciate wanting
>to move such a "slashdotted" site to a separate server (or server farm), in
>a timeframe less than the DNS normal-TTL-value times. Not doing so would have
>a serious negative impact on 100 little-domains, who may have SLA's with you.
>
>Replace "slashdot" with "IPO" or "new software release", or any of a dozen
>other usage-spike events; each customer has their own traffic trigger, and
>the ISP won't necessarily have adequate warning. Three days is way too long;
>even three hours can result in bad press, angry customers, and cancelled
>contracts.

How to move a hostname based virtual webserver:

I have to webservers A and B (10.0.0.1) and (10.0.0.2) and want to move 
site www.cust.com from A to B

The config on A is at the moment

<VirtualHost 10.0.0.1>
ServerName www.cust.com
DocumentRoot ...
</VirtualHost>

Now move the data to B, change the nameserver entry for www.cust.com to 
point to 10.0.0.2 and create a www2.cust.com also to point to 10.0.0.2. The 
config file on B becomes

<VirtualHost 10.0.0.2>
ServerName www.cust.com
ServerAlias www2.cust.com
DocumentRoot ...
</VirtualHost>

and the config on A becomes

<VirtualHost 10.0.0.1>
ServerName www.cust.com
Redirect / http://www2.cust.com/
</VirtualHost>

So all request still coming in into A are redirected to the new name www2 
(no DNS cache) and the DNS servers that are up to date go directly to B. 
Wait some time and remove the www2 entry from the DNS and clean up the 
config files.

Hope this helps somewhat

Regards

Niek Rijnbout
Knoware.