Why are using Docker then? I have little experience with Ruby, but for PHP projects we're still using ye olde way. Deploys are hot and do not interrupt requests

Why are using Docker then? I have little experience with Ruby, but for PHP projects we're still using ye olde way. Deploys are hot and do not interrupt requests, just as you described (it pretty much comes down to running `composer install && rsync` in CI — there are more complicated solutions like capistrano, which I've also used, but they don't seem to provide enough features to warrant increased complexity).