Wow. Given all the hype around docker, I'm really surprised nsenter type functionality isn't part of the core. Glad I'm using FreeBSD where running a shell in your jail is just 'jexec my_jail bash'. Compare that to the rigamarole described in the article. Maybe the docker guys will benefit from just reviewing the tooling for existing systems. I also recommend a look at ezjail-admin.
nsenter is part of util-linux, which means it will eventually make it into pretty much every Linux distro around. The functionality doesn't belong in Docker, because it isn't Docker specific - all it depends on is cgroups, and cgroups is a kernel feature, not a Docker feature.
Once it's in there, a "jexec" equivalent would a couple of lines of shell script.
