Layer 7 Load Balancing
One of the great things about late-model load balancing hardware is the ability to balance on data from the application layer (layer 7 of the OSI model). Traditional load balancers balance traffic based on the virtual IP that was assigned to a cluster. Requests sent to the virtual IP are routed to a destination based on the algorithm used on the nodes in that cluster. With layer 7 load balancing, specific information within the request itself can be used to balance the request to the appropriate destination.
INetU used this technology primarily on our Cisco ACE 4710 load balancers. This dedicated network appliance is capable of various layer 7 functions, ranging from simple keyword or response code health probes to full-fledged layer 7 load balancing. A common example of request-based decision making is static content hosting. Images, style sheets, scripts and so on may be served up by a content delivery network that is standalone from an application platform. To implement this, we can simply create a classification on the load balancers as follows:
class-map type http loadbalance match-any PICS
3 match http url /*.jpg
4 match http url /*.png
When the above is assigned to a policy map in a config, any traffic that matches the pattern will divert it to a serverfarm unique to that traffic. Any traffic not matching will be routed along the standard path to one of the many application server nodes it resolves to based on the conventional distribution algorithm.
