When hotmail ran of FreeBSD what software was used for clustering?

When hotmail ran of FreeBSD what software was used for clustering ?

Wikipedia states FreeBSD was used as a web server -- not the back end application.

"Hotmail initially ran under Solaris for mail services and Apache on FreeBSD for web services, before being partly converted to Microsoft products."

See citations 15 thru 17 in https://en.wikipedia.org/wiki/Outlook.com -- and in particular, citation 17 is the Microsoft Technet Planning Guide on FreeBSD migration - https://technet.microsoft.com/en-us/library/bb496990.aspx -- note the section on the "Pre-Windows 2000 Environment."