[Charlug] Web-server Farm - Networking Question

[Jared Watkins]

I don't believe it's possible to do what you want with only one ip.  
There is the concept of name based servers with apache.. but that has to 
be handled inside the application.  I don't know of any  generic way of 
doing that with other services such as SSH, mail etc. What you are 
wanting to do goes against how tcp networks are designed to work.  =]  
It may be possible with some combination of iptables and the advanced 
route functionality or load balancing code.. but I'd say it would be a 
kludge at best.  If you are talking only web (port 80) traffic that is 
fairly easy.. but generically setting up several virtual machines to 
completely and separately share an IP is something else entirely.

Also.. this comment about one VM 'blowing up' and not affecting the 
others is dubious.  If say some badly written website code has a runaway 
process it can affect the other systems.. either though CPU usage or 
IO.. if say a process ran out of memory and caused heavy swapping.  Just 
something to think about.  Sometimes there isn't a good substitute for 
having the right tools to do a job.

Thanks,
Jared




David Simmons wrote:
> I know what I'm hoping to do....I need help in understanding which 
> technology/buzz-word to research and RTFineM on.
>
> Situation:
>
> Physical CentOS server with a single, static IP address....with 
> multiple virtual machines - each VM (also linux / CentOS based) set up 
> for web-hosting (LAMP with ssh/ftp access).  Say VM1 hosts 
> www.somesite.com.....say VM2 hosts www.anothersite.com.....and say VM3 
> hosts www.finalsite.com
>
> I'd like to setup DNS to point to the single 'real-world' address - 
> but have the individual VM respond to the request.
>
> What technology do I use so that all of the virtual machines are seen 
> on the 'real' static IP address to the world?.....so that people on 
> the internet can SSH into their own box (which is just a VM on the host).
>
> I've been researching Multi-homing.....and Linux Virtual 
> Server.....but some of the howto's/docs are ancient.
>
> Any book / site / howto suggestions?
>
> Thanks in advance - Dave
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