How can I install passenger-nginx from Ansible?
Since you're on Ubuntu, just use Ansible to install the Phusion Passenger Debian packages (click on "Ubuntu") through apt-get. It works exactly the same as apt-getting anything else, is much easier than installing using RubyGems, and even installs all necessary dependencies for you (including Ruby itself!)
Breaks because Ansible now uses the user_install option for gem installs by default, as of Ansible 1.3
http://docs.ansible.com/gem_module.html#gem-manage-ruby-gems