What goes into releasing a patch to the public?

In general terms, because specific would take too long. Typically the process starts when QA gives the green light. Then the checklist happens to make sure everything is ready on the backend. With PTU they're moving a copy of the build to all the servers simultaneously. It's quite tricky, but they upload to a server that players can't see while other servers are running and then when that server has been green lit, then they'll begin the uploading process for the patch to the launcher. Then after some final tests and making sure everything is golden, they'll flick the switch and it goes live.