"""
Let's take a step back here. Do you really want Docker-in-Docker? Or do you just want to be able to run Docker (specifically: build, run, sometimes push containers and images) from your CI system, while this CI system itself is in a container?

I'm going to bet that most people want the latter. All you want is a solution so that your CI system like Jenkins can start containers.
"""

c'est plus complet en anglais: http://en.wikipedia.org/wiki/5_Whys