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April 14, 2004
Configuring Servers for Load Balancing
For load balancing our http and https traffic Tufts NOC uses a Foundry ServerIron switch.
I'm not an expert on load balancing but it seems like the method we're using is about as good as you can get. The DNS entry for the load balance URL (lb.tusk.tufts.edu) points at an VIP (virtual ip) address assigned to the load balancer. That VIP address is also assigned to a second loopback interface on each of the load balanced machines. Assigning the VIP to the loopback keeps it hidden, but allows the server to respond to traffic to that address.
When a request comes to the load balancer it rewrites the request packet to one of the real server ip addresses (based on a configuration options and existing connections to machines) and puts it back on the wire. The real server (not load balancer) will then respond to that request, leaving the remaining communication to happen directly between the client and the real server. Seems like an efficient way to balance traffic.
Assigning the second loopback ip address is simple, steps outlined in the Foundry docs.
The Foundry documentation has everything you'd want to know.
Posted by mike at April 14, 2004 10:32 PM
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