Btukfyl

I've read that you shouldn't ssh into a docker container. But why? I'd like to use a docker container as a replacement for a normal VM. What are the disadvantages? I know that this will create a lot of layers. But I could flatten my container on a regular base.

Can I use the container as a regular vm and what is the "worst case" that can happen?

No you can't use it as a replacement for a VM since you can only have one entrypoint on a docker container. You can not expose multiple services on multiple ports like you would on a regular virtual machine.

Docker containers are optimized around running single processes. Virtual machines are optimized around running entire operating systems.

At a technical level you generally can run something that looks like a full VM inside a Docker container, but it's a lot of hand setup. For instance, a typical systemd setup wants to manage several host devices and kernel-level configuration options, and your choices to run systemd are either (a) let it manage the host and possibly conflict with the host's systemd, or (b) manually figure out which unit files you can't run and disable them. All of the prebuilt Docker images run only single services (just MySQL, just Nginx, just a Python runtime, ...) and so you're also giving up this ecosystem.

A VM certainly gives up some amount of efficiency by virtualizing hardware devices and running multiple OS kernels, but if you really want to run a VM, it's not a huge performance loss; just run a VM if that's the model you want to use.