I’ve had some more thoughts about how to handle the photo/assets server. Rather than trying to rsync the images from the applications server I’m going to set up a caching proxy (probably using lighttpd but I may use Apache instead).
This will be massively simpler than periodically rsyncing images over and will require no change to the application. The only negative is that it won’t provide an online backup but I can address that separately.
While I’m migrating the applications server to the new hardware I’ll use rinetd to forward requests while I wait for the DNS to fully propagate.
UPDATE: Rather than lighttpd or Apache I think I shall use Squid as the proxy.