Unity is a J2EE application that serves requests to a variety of project sites at Codehaus.
It takes pages from Confluence converts them to XHTML, cleans them, and then rerenders them under an appropriate template.
Templates are customisable per site; however you will need to request this via Support.
If Apache can serve data from the file-system - e.g. a static resource; it will do this first.
All rendered pages are placed into memcached for easy access and high performance. The rendering pipeline is quite slow in the grand scheme of things and this caching improves performances massively.
Unity polls (every 60 seconds) Confluence for updates to pages; and flushes the cache appropriately. There are certain scenarios that are not detected (e.g. a header / navigation page change that affects all pages will not cause an automatic flush of all related pages); these should be documented.
As a precaution; Unity flushes cache contents after a period of time (30 minutes) to prevent these issues from building up.