Sure, but speed of rebuilds is important when you rebuild often, which is not my case. In my case the Dockerfile is easily replaced with a bash set -e script,

Sure, but speed of rebuilds is important when you rebuild often, which is not my case. In my case the Dockerfile is easily replaced with a bash set -e script, which has never gave problems to me: deboostrap, share volumes, aptitude install apache/nginx, mysql/postgresql, php/ruby, copy files, predeployment commands like f.e. bundle install, start services. And you have the advantage of starting services with `service start ...`, instead of reinventing init scripts.