I want to attach and control a systemd service like I do on a normal terminal, that's because my process running as a service has an input console and I'd want to be able to access that. I saw other solutions redirecting the stdin/stdout of the process to a tty using systemd configuration and then attaching with a tools like conspy or reptyr, but these don't work over an SSH connection. Is there any way I can do this?
If you do
man systemctl you'll find this option:
-H, --host= Execute the operation remotely. Specify a hostname, or a username and hostname separated by "@", to connect to. The hostname may optionally be suffixed by a container name, separated by ":", which connects directly to a specific container on the specified host. This will use SSH to talk to the remote machine manager instance. Container names may be enumerated with machinectl -H HOST.
This will allow you to perform any actions on a service on a remote machine that you could if you were local ( permitting you are working as a user with elevated permissions to do so ).