I need to host a subdomain-based SaaS application on a bunch of servers. Servers are xx1.example.com, xx2.example.com and so on. I want to have a bunch of yyy.example.com sites hosted on those servers.
Because sites are created on the fly, I need to be able to set up DNS records on the fly as well. A DNS wildcard zone doesn't really scale as eventually I will outgrow the first server and need to push new instances onto other machines. I therefore need to be able to point a specific subdomain to a specific IP address.
I looked around for API-based cloud DNS services (which would be great) but they seem outrageously expensive for my needs (lots of low volume instances). Rackspace has a free Cloud DNS service but it only goes up to 500 zones, and tech support told me they are rewriting the API so I would like to avoid their service for the time being.
Therefore I figured I will set up my own DNS server for these zones. Hence the questions: what's a good DNS server software for this specific need that will allow me to create zones without restarting?
Any suggestions? Thanks!