Facebook's web repo which includes all the PHP and JS for facebook.com and a bunch of other sites is one big massive repo. For development you claim out a serve

Facebook's web repo which includes all the PHP and JS for facebook.com and a bunch of other sites is one big massive repo. For development you claim out a server that has a recent checkout of the codebase. Right after claiming it it syncs in your personal commits/stacks you're working on, ready to rebase. You access that machine on a subdomain of any of the FB websites. As far as I remember it was something along the lines of 12345.od.facebook.com, but the format changed from time to time as infra changed. Client certificate authentication and VPN needed (that may no longer be the case, my info is 1y+ old). There was an internal search provider (bunnylol) that had tools like putting @od in front of any FB URL to generate a redirect of that URL to your currently checked out On Demand server. Painless to work with! Nice side benefit of living on the same domain as the main sites is that the cookies are reused, so no need to log in again.