Professional Microsoft IIS 8

Application Request Routing

In 2009, Microsoft released the first version of the Application Request Routing (ARR) module, which plugs into IIS 7.0 or greater and functions as a reverse proxy load balancer. This is an elegant solution because of its quick and clean installation and rich functionality. When looking for a load-balancing solution, ARR is worth serious consideration.

ARR leverages URL Rewrite for the routing, giving it powerful functionality for routing decisions. And because it sits on top of IIS, all the site bindings, security, error handling, and other rich functionality are readily available.

You may have heard ARR described as a reverse proxy, which technically is true; however, that description alone downplays its significance. ARR functions as a full-blown load balancer as long as your requirements fit within ARR's feature set.

Following are the main advantages of ARR:

• Cost—As long as you provide the hardware, the software costs only a Windows license. Windows Server 2012 Web Edition is the only requirement, and it's an affordable one.
• Staff expertise—Since ARR plugs into IIS, if you know IIS, the ARR learning curve is minimal.
• Performance—The first resource limit that ARR usually runs into is network. Because most networks support 1 Gbps or more, that says a lot. ARR can handle very large sites with ease.
• Flexibility—ARR offers full layer 7 load balancing, giving you flexibility to direct traffic based on any server variable, any part of the URL, cookie, ...