Page caching on separate servers

Has anyone here solved the problem of using page caching while
separating the web server from the app server?

Since page caching requires the app server to write files to disk,
and the web server to read those files, my guess is that the only
solution is to use some kind of network sharing.

NFS comes to mind, and along with it comes a long list of mental
notes that tell me to stay away from it since I don’t fully know what
I’m doing.

I don’t want my servers to stop to a halt if the nfs server gets a
cold. It’s just for caching, so it should be able to keep working
(albeit slowly) without the nfs server. Soft mounting seems like an
option, but it still has very long timeouts if it can’t reach the
file server.

Ideas? Suggestions? Alternatives? Tips?

Thanks,
Sebastian

PS: No, I’m not talking about fragment caching, which can use
memcache and other solutions. This is about full page caching that
requires the cooperation of rails with the front end web server.