Use the variable SSH_OPTIONS_PROXYCOMMAND

[lars18th]

What are you trying to do?

When remotely using the multipassd daemon from another machine, the multipass client might need for some commands direct network access to the instance. In that case it uses the MULTIPASS_SERVER_ADDRESS environment variable to know where the remote daemon is located. But if the connection to the daemon is made using some tunnelling technique, then you cannot reach the shell of any instance that is not using public addresses. A simple solution could be to add support for the SSH_OPTIONS_PROXYCOMMAND included in the libssh library, which is used to establish connections from the client to the instance.

You can read more about this var here: A description of what you want to happen.

What's your proposed solution?

Just by adding support for this option already included in the libssh library used in multipass, it would be possible to establish the necessary connection to the instance without direct network routing. For example, with a simple netcat/socat proxy command you can use a socks proxy opened in the ssh session used to connect to the multipass host. This is very simple and clear. And no code changes are needed. Just add the proxy command configuration when setting up the connection using the libssh library.

Additional context

One relevant issue related to this limitation: #309