VHS has an RFID door entry system for keyholders. Beta testing right now. Integrates with modified version of Membership Management Pro.
The problem with the door Arduino has mostly been bad solder joints/stranded wire shearing off. It was fixed (poorly) and pictures were taken so that if it breaks again, it should be easy to fix. In that case, it'll be a good idea to put some stronger wire on the protoboard and connectorize everything. If it doesn't break again, then it's good! Not touching it!
Along the same lines, if you put in the final screw of that mounting box, then it presses too hard on the shield and it disconnects/shorts something and everything stops working.
Currently the Raspberry Pi has a workflow that looks like this: Wait for RFID device Grab RFID code Send to server Receive AUTH/NOAUTH If AUTH, send door unlock
This is not a system that fails gracefully on internet outage. Irony - If internet goes down, no one is able to get into the space to fix internet.
The Raspberry Pi will have a local cache that it will fall back on in the event of losing internet connectivity.