Re: Connection-local login programs

Eshel Yaron <[email protected]> writes:

> Hello Michael, all,

Hi Eshel,

> I have a use case that I couldn't find a clean solution for, and I'm
> wondering if Tramp could provide a nicer way to handle it.
>
> In Kubed[0], we define a Tramp method called "kubedv2", which uses
> kubectl to interact with Kubernetes workloads, somewhat similarly to the
> "kubernetes" method from tramp-container.el.  Following a feature
> request from a user, we want the "kubedv2" method to work in multi-hop
> settings, in which the user uses Tramp to connect to some remote host,
> say via ssh, and then from that remote host they invoke a Kubed command
> that starts a two-hop Tramp connection using ssh for the first hop and
> kubedv2 for the second.
>
> The difficulty is that on the remote host (the target of the ssh
> connection), the user may need to specify a different kubectl executable
> to use as the tramp-login-program.  Kubed lets you specify which kubectl
> to use through a user option kubed-kubectl-program, and we always use
> the connection-local value of that variable so users can configure
> different kubectl to use on different hosts, but that doesn't naturally
> extend to our Tramp method, because the tramp-login-program is always
> taken from the specific value we put in tramp-methods when "defining"
> the method.
>
> Is there a better (or just more officially supported) approach that you
> would recommend?

All parameters specified by tramp-methods can be overwritten by
connection properties, see (info "(tramp) Predefined connection information")

In your case, you could do (untested)

--8<---------------cut here---------------start------------->8---
(add-to-list 'tramp-connection-properties
              (list "^/kubedv2:user@example\\.com:")
                    "login-program" "/another/kubectl"))
--8<---------------cut here---------------end--------------->8---

> Thanks,
>
> Eshel

Best regards, Michael.