This deployment of what's called "www" ("dub-dub-dub") is somewhat monolithic in the sense that it is large, but it is not really an "all-or-nothing" deployment

This deployment of what's called "www" ("dub-dub-dub") is somewhat monolithic in the sense that it is large, but it is not really an "all-or-nothing" deployment. It is tested internally (for at least 2-3 days) by employees (engineers and non-engineers), and then on a subset of servers, a larger subset, and so on. Performance, error rates, interaction rates, and so forth are compared between the incumbent and new-hotness versions for a reasonably reliable indication of issues throughout the rollout. More on the www push at https://www.facebook.com/video/video.php?v=10100259101684977 https://www.facebook.com/video/video.php?v=10100259101684977 Teams that run "services" (such as the one that powers the "typeahead" search bar at the top of Facebook) deploy their services separately, at whatever pace makes sense for them. These are almost never in tight lock-step with anything else, for the usual reasons.