I have multiple webservers with the same content, hosted across different providers. However, I can't seem to find a nice, simple failover solution. Load-balancing software (Pound, HAProxy, etc.) are unnecessary, and I need the flexibility to manage over 100+ domains, so the paid DNS failover solutions I've found are too expensive.

So far the simplest solution I've thought of is just to set a very low TTL (30min - 1hr) in each zone entry on my nameservers (running BIND). Then, continuously monitor each server, and temporarily remove failed servers from zone entries. But this seems like something that should be currently available.

I only have root access to different VPSes running CentOS. Any suggestions? Thanks!