Load balancing by custom queue length

I believe iControl is certainly a great option, with a few thoughts:

1. You would have to have an iControl script running on each server that can make (iControl) calls to the BIG-IP and alter its own weight, or a central server that polls the individual servers and makes a global weight adjustment.

2. If the former option above, because each server doesn't have knowledge of the other servers' loads, you'd have to have some static gauge by which to assign weight based on this server's number of files (ie. 2 files = weight 1, 3 files = weight 2, etc.). This of course wouldn't be a completely accurate scale.

3. If the latter option above, you could query all of the servers, take an average, and assign weights accordingly. This option can also be performed in two places: an iControl running on a central server, or if you can place a little scripted page in your web servers that simply returns the count of files, you can do all of this from an external monitor on the BIG-IP. For example, here's a PHP script that returns the file count:

Once you have all of the numbers in house, simply perform some local TMSH calls to adjust the weights of the individual members.