Visualforce and VPN

I'm looking to integrate my Salesforce implementation with an external database. I know that in most circumstances I would use 开发者_高级运维Visualforce with an Apex controller/extension to access the data, however the external database will require a VPN connection. Since Visualforce and any controllers or extensions are processed server-side, is there any way to do this through a VPN?

---

The simplest solution that occurs to me would be to expose the data via a web service and then write an Apex webservice class to call the data. I've done this several times when data was behind a firewall.

For more complex integrations, where you actually wanted to store the external data in Salesforce with more complex logic it could be useful to use an integration tool like Jitterbit or Cast Iron to do this for you.