Sometimes, during development or when fixing a deployed app, you want to get inside the container environment to poke around. Just to work out why the hell something did or didn't happen.

Right now it is difficult. Docker doesn't support it directly. There is a lot of demand for it:

https://github.com/docker/docker/issues/1228

You have to use nsenter, which is OK, but requires additional installation:

https://github.com/jpetazzo/nsenter

It looks as though an-almost-but-not-quite-the-same thing will land in Docker at some point:

https://github.com/docker/docker/pull/7409

And this shell is another attempt to make a very useful feature available.

Are you sure it is related to entering an existing container (and running a new process) ?

From reading the README file, it seemed to me it was only spawning a login shell process in a new container (not an existing one), and possibly resuming an existing container.

You are correct, dockersh is a shell. It spawns a "proper" shell (e.g. bash) in a docker container when you log in.

I feel this docker pain. But isn't an isolated process the point? I thought I read an article here recently that said, basically, if you're running an ssh server in your proc then you're doing it wrong.

I feel like having completely isolated processes is ideal but not always or even usually needed.

I know the phusion/baseimage argues against excessive isolation:

https://github.com/phusion/baseimage-docker#docker_single_pr...