[Galene] Re: coturn config

[Juliusz Chroboczek <jch@irif.fr>]

> I'm already using this (with git revision d2f7010) since 2+ days. No
> issues so far.

Excellent.

> How to ensure that it survived key rotation?

Keep Galène running for more than 24h after the initial key is generated
(which happens the first time a client joins).  If the group is still
accessible, then key rotation was successful.

I've got unit tests for key rotation, but not for key rotation.  See
ice/ice_test.go.

> Does key rotation affect existing TURN sessions?

No.  It doesn't even affect existing client sessions, you need to leave
the group and re-join in order to get a new key.  The protocol supports
rotating a joined client's keys, but doing that properly would require
maintaining key age for each client, so I didn't bother for now.

A new key is generated every 2 to 5 minutes, and it has a validity of 24h,
so you'll only run into the issue if you remain connected for (24h - 5min).

In case anyone wants to hack on it, here's what's needed:

  - maintain credential age somewhere in the client structure;
  - at the right time, launch a goroutine to send
    { type: "join", kind: "changed"} to all clients nearing expiration;
  - for extra credit, trigger an ICE restart for all streams to and from
    affected clients so that existing streams pick up the new TURN
    credentials; not sure if that's better done in the client or in the
    server (either side can trigger a restart).

> Maybe some logging would be good.

Yeah.

-- Juliusz