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How and why the leap second affected Cloudflare DNS

Blog post from Cloudflare

Post Details
Company
Date Published
Author
John Graham-Cumming
Word Count
1,044
Company Posts That Month
6
Language
English
Hacker News Points
61
Post removed?
No
Summary

On January 1, 2017, a negative value in Cloudflare's custom RRDNS software caused some DNS resolutions to fail for customers using CNAME records. The issue affected approximately 0.2% of DNS queries and less than 1% of HTTP requests during the outage. The problem was quickly identified and fixed within 90 minutes, with a global rollout by 6:45 UTC. The root cause of the bug was the belief that time cannot go backwards, which led to negative values being recorded in server selection code. Cloudflare has since inspected all its code for other leap second-sensitive uses of time intervals and apologized for any inconvenience caused to customers.

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