What I'm also not sure of is how to deal with cookies and ACS - presumably a user who gets a cookie from webserver A has to be redirected back to webserver A rather than webserver B on their return. Am I right? Is this straightforward with a device lke the Cisco one above? How do people recommend such a thing is dealt with?
I'm the one who suggested Big/IP. I see them on
bay for several thousand $US, just so you know what you're up against.
They do connection-based load balancing. The short story is that you give Big/IP's external interface the IP of your www. URL. You configure the Big/IP to do load balancing among a number of servers. It will rotate each incoming connection, following some algorithm or another for 'rotation', among the servers you've identified.
You can do this per-port, per-IP. So say you want to route port 80 to machines A, B, C, and port 443 to beefier machines D, E, F, and G. No problem. Need to ssh into your farm? Route port 22 somewhere else.
etc. You get the idea, I hope.
There are free + libre solutions for Linux that do the same thing. But they're also huge hassles. If you look at the Big/IP hardware and add the time you'd spend configuring a Linux load balancing and failover system, big/ip ends up more or less worth it.
Particularly if you want to add failover features (by buying a second big/ip) then it gets even more worth it.
To directly answer your question, this is not an issue with cookies. The browsers all think they're connecting to the same machine. Unless, of course, you're keeping client state on the web server (tied with cookies). In that case, you have a severe architectural problem and you'll have to find another form of load balancing. My bank appears to have this problem, since every time I do web banking, I get sent to webbankingXX.tdaccess.com for random values of XX.
