Problem with session persistence using CARP when load balancing a McAfee Web Gateway cluster using progress page for downloads
We have a cluster of 14 McAfee Web Gateways and about 15000 users connecting to them from a few dozen Citrix farms. Previously we have been using source address persistence, which works fine until one of the pool members are taken offline then online again. All clients will then be load balanced to another available pool member and the one that was offline gets no traffic after that. Enter hash persistence using CARP. The idea is simple, use something like the host header and make a hash of it then load balance using the CARP algorithm. This also works great, except when downloading files. McAfee Web Gateway works like this; it downloads the file for malware scanning before delivering it to the client. Meanwhile it displays a progress page to the client. The problem is that with hash persistence quite often the progress page will show an error. This is because I get loadbalanced to a different pool member than the one showing me the progress page. I really would like to use hash persistence, but I'm not sure there is a proper workaround for this. Any suggestions? What are you guys doing for persistence to web caches?