BTW, copying the entire app to a new directory did begin to take a while after a couple years, and I never got around to solving that. However, I believe it's q

BTW, copying the entire app to a new directory did begin to take a while after a couple years, and I never got around to solving that. However, I believe it's quite possible to implement COW: hardlink the hell out of the current version, then beat rsync into replacing differing files instead of updating them in-place. The hardlinking part could be done before the deployment even begins—or you could copy the files instead of hardlinking to avoid altering them accidentally. Or could probably just use overlayfs or something like that. Note that, while containers can give you COW, they shouldn't really be necessary for the files of the app. And with php-fpm, changing the app dir is faster than restarting containers: it's actually done via changing the Nginx config.