But you are right there is no reason why you couldn't have two instances of the php app runing and switch between them. For some reason the PHP deployment services i've used seem to use the filesystem approach and i doubt it's laziness or incompetence.
And all that may be true for a trivial website. If you've written a personal project with 10,000 hits per year, YOLO. Go for it. The odds of it affecting one of those users is vanishingly tiny, and so what if it does? But if you're hosting something like a Wordpress site for a large company with lots of traffic, it's crucial to understand why "just rsync the files over" is not an acceptable deployment method.
I have a feeling you want to dunk on poor dumb PHP developer but like Forge is by the people who created Laravel. I believe they would put some thought into it. Maybe just maybe small chance of one bad request is not such a bad deal.
> Maybe just maybe small chance of one bad request is not such a bad deal.
If your company is OK with that, seriously, sincerely, right on! Keep doing this and move on to other problems.
If you have very long database query and you update your app in middle of it using blue-green load balancer you get to same production error. It is the same thing just implemented slightly differently because of PHP characteristics allow this and with different systems you have to use different strategy.
So yeah have good feeling about us PHP devs having bad deployment strategies.