Here's a quick tip that will help people who have installed OS X Lion Server. Lion Server includes a Wiki Server that (in my opinion) is one of the best Wiki Server's out there. Full WYSIWYG editing and its very simple for anyone to use. The whole interface is simple and polished. The whole thing is built on Ruby, and serves as a great example of a Ruby Web App.

However, sometime the Wiki Server won't start, causing problems for the Web Server. Here is one solution to this problem.

If you have the Wiki Server set to "On" and you see a message like "503 - Service Not Available" when visting a website that is hosted on your Lion Server machine, take a look in /var/log/system.log.

If you see:

Nov  5 13:34:35 home com.apple.collabcored1[56384]: /Library/Ruby/Gems/1.8/gems/bundler-1.1.
pre.1/lib/bundler/runtime.rb:31:in `setup': You have already activated rack 1.2.3, but your 
Gemfile requires rack 1.2.1. Consider using bundle exec. (Gem::LoadError)
Nov  5 13:34:35 home com.apple.collabcored1[56384]:     from /Library/Ruby/Gems/1.8/gems/bun
dler-1.1.pre.1/lib/bundler/spec_set.rb:12:in `each'
Nov  5 13:34:35: --- last message repeated 1 time ---
Nov  5 13:34:35 home com.apple.collabcored1[56384]:     from /Library/Ruby/Gems/1.8/gems/bundler-1.1.pre.1/lib/bundler/runtime.rb:17:in `setup'
Nov  5 13:34:35 home com.apple.collabcored1[56384]:     from /Library/Ruby/Gems/1.8/gems/bundler-1.1.pre.1/lib/bundler.rb:109:in `setup'

This means that the Collabcored application (ie the Apple OS X Wiki Server) is configured to use Rack 1.2.1. But it appears that Rack 1.2.3 is installed. (This is usually installed by later Web Apps that you might have installed). To solve this, try removing Rack 1.2.3:

sudo gem uninstall rack -v 1.2.3

This will give:

Successfully uninstalled rack-1.2.3

Then bounce the Wiki Server by turning it on and off in the Server Application. (Server.app). All should now be well...! (And yes, there should be a more elegant solution, problem by editing the Wiki Server configuration. This is something I am looking into...)