A bit of a background on the config to give you an idea of our setup.
We have a hardware firewall that supports 250k concurrent TCP connections in the front. Behind that we have a server running HAProxy that handles the RDNS for the network and pushes the calls to 2 app servers where wordpress is running. They are rsync'd together via a passwordless ssh cronjob. They in turn are connected via hyperdb to a mysql server cluster.
Now the problem is we have a custom api that allows them to bring in media files stored on the main site into their site on the multisite network, all cool works like a dream. However we just upgraded our network app servers to ssd storage in raid 10 format so we are limited on physical space on the ap servers. hence the need to offload the media 99% of which are videos to our CDN where we have an unlimited storage plan.
Now the ideas I have come up with are.
A. Rsync the files to the cdn with the delete source option, nice and clean solution but then the database cluster would need updating with the new image urls.
B. Just use a pull zone on the CDN to grab them as they are called and configure it in wordpress as the media library, problem is if we delete the original files and then the cdn does a check for caching and sees the original gone it will flush it from the cdn.
C. Use a push zone so any files uploaded to wordpress are sent directly to the CDN, but i havent found a successful way of setting the media library to use a totally external source for storage when nothing is being held locally at the same time.
any feedback is welcome.