ssh_light - a simple ssh transport plugin

[yakutovicha]

Is your feature request related to a problem? Please describe

When setting up an AiiDA computer, I often encounter a problem that, despite ssh being configured and working, the verdi computer test command fails. This is because relationships between the core.ssh transport plugin and the ssh configuration found in .ssh/config are somewhat convoluted.

This specific point was causing a lot of frustration when using AiiDA because I was never sure that my newly set up computer worked fine.

In addition, the ssh configuration requires several parameters, which are not transferred when the computer is imported into a new database. From this point of view, there is no reason to store the connection information in AiiDA.

Describe the solution you'd like

I propose implementing a simplified plugin that exclusively relies on the .ssh/config. This will drastically minimise the effort to configure ssh transport for a computer. This approach will ensure that if ssh works, the verdi computer test will work too. Well, most likely 😅 .

I would base this plugin on fabric, which is a more high-level library w.r.t. paramiko and is recommended by paramiko developers for high-end client applications.

Describe alternatives you've considered

I also considered using the asyncssh library as an asynchronous alternative to fabric/paramiko. But it turns out that relying on asyncssh is a challenge currently. Since AiiDA has some asynchronous methods and there can be only one event loop, the following appears to be impossible:

async function from aiida -> sync transport plugin method -> async method from asyncssh

Therefore, at the moment, we stick with fabric, which provides high-level ssh functionality.

Additional context

The current implementation of the ssh transport plugin tries to provide users with a very fine-tune configuration. But the further one goes, the more complicated and prone to errors it becomes.

I believe that using the dedicated library to automatically handle the ssh configuration is the right way forward.