ubuntu - CNAME : how to setup DNS to return A record based on website?

I have a query regarding setting up servers.

Suppose I have multiple websites to host.

foo.com
bar.com
hello.com

I may or may not to have specific servers for them. Suppose an arbitrary configuration is something like this (with the respective domain registrar)

foo.com  A  1.1.1.1
bar.com  A  1.1.1.2
hello.com A 1.1.1.1

What I would like is to give each website a universal domain to point to instead of an IP (since IP can change).

something like the following.

foo.com CNAME service.com
bar.com CNAME service.com
hello.com CNAME service.com

From what I have understood about DNS so far,

Queries

1. I think I will need to setup a DNS server at service.com which returns the appropriate records.
   
   
   
   
   • Is this correct?
   
   
   


2. If so what if domain is held with a domain registrar? such as dreamhost. How to handle it then?
   
   
   
   
   • Since they respond to DNS queries, how do I insert that layer of indirection?
   
   

Achieve transparent server migration from client's perspective

Ultimately what I would like to achieve is that if I were to one day host hello.com from a different server, I would only have to modify in 1 place at the server rather then tell the client to change their DNS config.

Additional Info:

I use rackspace, they also have something called reverse DNS. Is that useful?

I noticed for google Apps - we always point to ghs.google.com and they forward the request to appropriate IP. So it must be possible, but I just can't figure out how to achieve it.

Answer

You'd need a separate cname per site. Something like:

foot.com CNAME foo.com.service.com
bar.com CNAME bar.com.service.com
hello.com CNAME hello.com.service.com