jm + leap-smearing   2

Leap Smear  |  Public NTP  |  Google Developers
Google offers public NTP service with leap smearing -- I didn't realise! (thanks Keith)
google  clocks  time  ntp  leap-smearing  leap-second  ops 
january 2017 by jm
How and why the leap second affected Cloudflare DNS
The root cause of the bug that affected our DNS service was the belief that time cannot go backwards. In our case, some code assumed that the difference between two times would always be, at worst, zero. RRDNS is written in Go and uses Go’s time.Now() function to get the time. Unfortunately, this function does not guarantee monotonicity. Go currently doesn’t offer a monotonic time source.


So the clock went "backwards", s1 - s2 returned < 0, and the code couldn't handle it (because it's a little known and infrequent failure case).

Part of the root cause here is cultural -- Google has solved the leap-second problem internally through leap smearing, and Go seems to be fundamentally a Google product at heart.

The easiest fix in general in the "outside world" is to use "ntpd -x" to do a form of smearing. It looks like AWS are leap smearing internally (https://aws.amazon.com/blogs/aws/look-before-you-leap-the-coming-leap-second-and-aws/), but it is a shame they aren't making this a standard part of services running on top of AWS and a feature of the AWS NTP fleet.
ntp  time  leap-seconds  fail  cloudflare  rrdns  go  golang  dns  leap-smearing  ntpd  aws 
january 2017 by jm

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