I think this is the write-up where the author explains how he developed it: https://debugged.it/blog/ssh-direct-to-docker/
Have not read it yet, but looks interesting, because I was curious how you implement a SSH-server replacement.
golang’s ssh package supports that. It is easy to implement a new sshd alternative.
Here is a tiny implementation https://github.com/ContainerSSH/MiniContainerSSH
It’s a super barebones implementation of ContainerSSH to demonstrate how it works
Like the README says, this seems incredibly useful for teaching labs and workshops. I am really curious how this performs on different sizes of k8s cluster to see how much capacity you need relative to audience size.