I was working on a Storm project where the work nodes run in a tightly controlled grid environment. So, directly RDBMS access through traditional mechanism is prohibited since only certain ports are open for inbound and outbound traffic. So, I ended up writing a quick and dirty HTTP proxy that exposes certain MySQL database operations using REST API calls.
Then I just found this is actually quite a common use case and several people have written generic HTTP servers to expose REST APIs for database access.
One such project is jdbc-http-server, really handy. I will see if I can replace my own version with that.