{"UUID":"5cbc4e4d-d491-4576-a9fe-6f60ca05c9d8","URL":"https://web.archive.org/web/20211104160742/https://blog.cloudflare.com/how-and-why-the-leap-second-affected-cloudflare-dns/","StartTime":"0001-01-01T00:00:00Z","EndTime":"0001-01-01T00:00:00Z","Categories":["postmortem"],"Company":"Cloudflare","Product":"","Description":"Backwards time flow from tracking [the 27th leap second on 2016-12-31T23:59:60Z](https://hpiers.obspm.fr/iers/bul/bulc/bulletinc.52) caused the weighted round-robin selection of DNS resolvers (RRDNS) to panic and fail on some CNAME lookups.  Go's `time.Now()` was incorrectly assumed to be monotonic; this injected negative values into calls to `rand.Int63n()`, which panics in that case."}