connecting from app engine to an external database via JDBC

[Robert Dyas]

From App Engine is it possible to make a JDBC connection to a remote database in another cloud or on-premises?

I see that your sockets API is limited, so wondering if this would work.

[paynen]

You're correct that JDBC connections on arbitrary ports are not going to work on App Engine, without seriously patching the driver and having it use the Sockets API, which is not the same as general sockets. However, JDBC connections to Cloud SQL are possible, as described in the docs. On Managed VMs, you have unrestricted access to the filesystem, network interfaces, process control, etc., so the App Engine sandbox doesn't apply and standard JDBC will easily function.

I hope this has helped answer your question, and feel free to browse the docs to learn more about the App Engine runtime, or Managed VMs on the other hand.