Using salt-ssh with agent forwarding


Sven Vermeulen Sat 26 March 2016

Part of a system's security is to reduce the attack surface. Following this principle, I want to see if I can switch from using regular salt minions for a saltstack managed system set towards salt-ssh. This would allow to do some system management over SSH instead of ZeroMQ.

I'm not confident yet that this is a solid approach to take (as performance is also important, which is greatly reduced with salt-ssh), and the security exposure of the salt minions over ZeroMQ is also not that insecure (especially not when a local firewall ensures that only connections from the salt master are allowed). But playing doesn't hurt.

Using SSH agent forwarding

Anyway, I quickly got stuck with accessing minions over the SSH interface as it seemed that salt requires its own SSH keys (I don't enable password-only authentication, most of the systems use the AuthenticationMethods approach to chain both key and passwords). But first things first, the current target uses regular ssh key authentication (no chained approach, that's for later). But I don't want to assign such a powerful key to my salt master (especially not if it would later also document the passwords). I would like to use SSH agent forwarding.

Luckily, salt does support that, it just forgot to document it. Basically, what you need to do is update the roster file with the priv: parameter set to agent-forwarding:

  priv: agent-forwarding

It will use the known_hosts file of the currently logged on user (the one executing the salt-ssh command) so make sure that the system's key is already known.

~$ salt-ssh myminion