Will likely be serving multiple independent WordPress websites and am trying to determine the best general approach. At present I'm looking at two VPS, one with Apache/PHP/FastCGI and another running MySQL with a private interface between the two. This allows me to tune and scale the web server and database server independently, if necessary. On the other hand, it introduces some additional complexity, requires a heavier MySQL process, creates more chance of bottlenecking at the database, and probably exposes more attack surface-area.
The other approach is to put all services on one, larger VPS, and simply add resources or additional self-contained nodes as necessary.
Does anyone have specific experiences with the pros and cons of both approaches? Additional suggestions? Recommended resources?