by
Brian Madden
Now that
Microsoft's RDP protocol included in Windows Server 2003 has
basically the same functionality as
Citrix's ICA protocol, a lot of people are
beginning to think about how to load-balance multiple Terminal Servers when
Citrix MetaFrame is not used. Of course you can use Microsoft's own
network
load-balancing services (part of the Enterprise Version of Windows Server 2003).
However, this is based purely on network utilization, and you're limited to 32
servers that must all be on the same subnet. A more flexible solution is
Tarantella / New Moon's
Canaveral iQ, but that still costs $150 per user.
Another alternative is to use a hardware load-balancing
device. In the past, people have been afraid of these, thinking that they're
nothing more than IP-based network load-balancers. Well, times have changed!
Windows Server 2003 exposes all of the performance counters and the
session
directory to external devices (i.e. these load-balancers). Now, you can have a
hardware load-balancer that can intelligently route users to a server based on
processor utilization or the overall number of sessions. Commonly referred to as
"Layer 4-7" routers (since that's the part of the OSI stack they operate in), you buy them based on the number of servers you
have, rather than the number of users you have. A $2000
load-balancer might seem expensive until you realize that it can
support 8 servers, each with 100 or so users. $2000 for 800 users is not
bad. (Of course these load-balancers can approach $20,000-$60,000, so they're
not always the best solution.)
So, who makes these load-balancers? Several companies do--some that you've
heard of and some that you haven't. The post popular ones for Terminal Server
environments are F5's BIG-IP line of
products. Nortel offers hardware
load-balancing via their
Alteon
products, and Foundry's
ServerIron products do the same.
Finally
Cisco's 11500 series of routers also offer Layer 4-7 content switching.
All in all, there may be a void in the market for a simple, easy, and cheap
software-only load-balancing solution. Until then, these hardware devices do
everything that's needed and more.
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