[mogui]

In case (c) or (d) how can a layer leverage the distributed facilities that FDB gives? I mean if I have clients that connect to a "layer service" that is the one who talks to FDB, I have to manage "layer service" scalabily, fault tolerance etc... by myself.

[voidmain]

Yes, and that's the main advantage of choosing (a) or (b). But it's not quite as hard as it sounds; since all your state is safely in fdb you "just" have to worry about load balancing a stateless service.

[mogui]

got it, what will you suggest to do something like that? a simple RPC with a good async framework I've read, like what? an RPC service on top of Twisted for python, similar things in other languages?

thanks :)