How to set up OSG gatekeepers?

There is a detailed documentation here

A couple of notes:

1) when USATLAS user applies for host certificate, at the page of https://pki1.doegrids.org/, in the "Contact Information" block, when asked for the "Affiliation (registration authority)", please specify "PPDG" if your institute is not in one of the displayed affiliations like LBNL. Then you indicate that you are USATLAS collabrator in the comment box.

How to make the site ATLAS ready?

Basically if you follow the steps described in above link to finish the OSG CE installation, your site will be ready for any VO applications, including ATLAS.

But site admin has to make sure that the site actually shows up on GridCat and Monalisa of OSG. If you are done with installation and don't find your site on the above monitoring tools, please send email to the support list.

After the site is ready, VO application people will install the VO software, like atlas releases, on the sites, and send jobs. But this part is mainly handled by application users, no involvement needed from the site admin. In the future, once edge service is defined, extra setup and configuration might need to be done by the site admin, but that is the future.