[Ovmsdev] Reverse connections (module -> developer)

Stephen Casner casner at acm.org
Mon Feb 10 14:01:52 HKT 2020

On Mon, 10 Feb 2020, Mark Webb-Johnson wrote:

> I am curious, @Steve, if you implemented any controls for
> restriction of engineer access? For example, in this OVMS
> requirement, say a developer configured his module to SSH tunnel
> back to the central control server, then he can SSH to that control
> server to tunnel into his module. But what is stopping other
> developers also connecting to his module? Presumably everybody is
> just connecting to on the central controls server?

That wasn't a requirement for our implementation.  Access to the
phone-home server was restricted to the set of support staff and
engineers responsible for supporting the systems that phone home, but
all of those support staff and engineers were allowed to access any of
the connected remote devices.

For OVMS, you are envisioning a much more general problem where a
large number of developers would want independent remote access to
their OVMS devices.  Trying to provide that through one shared
call-back server would be more complicated.  But the only reason for
the shared call-back server would be to free those developers from
needing to set up a globally addressable server of their own.  I'm not
sure we need to do that.

I was thinking about a scenario much more like the one I had in my
job.  The server would only be accessed by a small set of core
developers -- those, like you, who are willing and able to help
diagnose user problems.  Those developers would have access through
the server to any of the OVMS units whose owners have chosen to grant
that access by enabling the callback.  Those owners would do so
because they trust the developers and want their assistance.

> I am also concerned about performance. For console access, that
> shouldn’t matter - but for can bus dumps we need every bps of speed
> we can get.

Assuming some reasonable server machine, I would not expect that to be
the bottleneck.  My guess is the limiting factor would be the
networking software in OVMS.

                                                        -- Steve

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