Re: [chrony-users] Server failover

[Miroslav Lichvar <mlichvar@xxxxxxxxxx>]

On Fri, Aug 12, 2022 at 11:04:15AM -0400, Aaron Ball wrote:
> What's the best way to get chronyd to promptly stop using a server, from
> the server side? So the best option I have right now is to restart with an
> alternate config file with "local stratum 15" in place of the refclock line.

Yes, increasing stratum should be the fastest way to deselect the
server on the clients, assuming they use the default stratum weight.

An issue with the local directive is that the server's root delay and
dispersion will be zero, which can cause it to become a falseticker
among the other servers and the measurements will have a larger weight
when the server comes back and is selected again, which may cause an
oscillation.

Instead of the local directive I'd suggest to use the same refclock
directive but modified with "stratum 14 delay 1". With the dumpdir
directive and -r option the server change should be almost instant.

> We use redundant time servers in each of our datacenters, and we'd like to
> actively switch away from time servers before their scheduled reboots,
> because the estimated error that accumulates on our clients while waiting
> to notice that a server has gone away can be too high for our standards.

As Kevin explained, ideally clients should handle that on their own. I
understand you have tight requirements on accuracy. Have you tried
setting reselectdist on clients to 10 microseconds or less?

-- 
Miroslav Lichvar


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