RE: [chrony-users] Isolated time domains

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On Thu, Dec 5 2013, Bill Unruh wrote:

> Eg, he says that he wants to keep all of the computers to within 1 sec. But
> what happens if one of the clients suddenlyfinds itself 3 hours out? Are all of
> the other clients then supposed to go out as well to keep themselves in sync
> with that client? How would they do that? And if not, why is the server
> special that all should run after its crazyness?

The clients should, and do already, follow the server no matter how "crazy" it may seem to the outside world.  The server in a single site location is the source of truth for what UTC is.  All clients on that site must obey or not participate in operations.  In fact, these clients will already make whatever jumps in time are needed to bring themselves in line with the server (usually as part of connection startup).  If one client of the server decided that it knew better than the server and adjusted to some other reference of UTC than it just functionally won't work.  That's why the server is special.

So, in order to avoid introducing risk into what is already operating, I am looking for a way to slowly move the server's time to UTC as indicated by a remote NTP server while the clients happily follow along.  For server's with more extreme offsets from UTC, they can be manually stepped when operationally appropriate.

As an experiment, I've got two instances of chronyd running on a server.  One instance is sourcing the external ntp servers and taking care of the server's local clock.  The second instance, is just serving up the local clock to the clients (on a different UDP port).  This is producing what I've been describing, although I'm not a big fan of having two instances running since I don't understand the chronyd/NTP internals well enough to know of any gotchas that may be hiding.  Also, requiring the use of a non-standard port is less than ideal, in case an ntp client doesn't support it.


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