We have a big pool of web servers for a particular web application we develop on. Our clients currently point there domain or a subdomain using a A record to one of our servers. As we are growing we need to be able to dynamically move the sites to different servers on different IPs which means asking the client to update their DNS, which we don't/won't want to do. By dynamically I mean if a server goes down we want to re spawn the data on a new server, change where the domain points to and have the application back up with in seconds/few mins.
My first thought was to use our DNS servers but many clients can't change their NS servers to ours. And can only add an A record to a single static IP.
So I had a look into using a layer of proxy's, like HAProxy which can route the traffic by hostname. The problem with this is I need to be able to add a new domain every few seconds and HAProxy uses a config file and you have to reload the service to apply the new config. Which won't work well doing it every few seconds.
Is there anyway I can do this with a proxy application or DNS application?