This site shows the status of various ROS sites including:
The ROS wiki: https://wiki.ros.org
The ROS website: https://www.ros.org
The ROS build farm: http://build.ros.org
The ROS package repository http://packages.ros.org
The ROS documentation site: http://docs.ros.org
As well as several associated services used to provide functionality to the ROS community.
If you find an issue that you think we're not aware of please open a ticket at: https://github.com/osrf/infrastructure/issues
If the ROS wiki: https://wiki.ros.org/ is down there are several mirrors including: http://mirror-ap.wiki.ros.org/ in Singapore and http://mirror-eu.wiki.ros.org/ in Ireland.
The autogenerated documentation from docs.ros.org is also available on mirrors including: http://mirror-ap.docs.ros.org/ in Singapre and http://mirror-eu.docs.ros.org/ in Ireland
Other mirrors are listed at https://wiki.ros.org/Mirrors if the wiki's offline try Google's Cache: https://webcache.googleusercontent.com/search?q=cache:wiki.ros.org/Mirrors or one of the Mirrors of the Mirror list: http://mirror-ap.wiki.ros.org/Mirrors