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From a cloudflare blog post on this, their public DNS resolvers were getting 30x their usual traffic. Presumably that was the case for DNS resolvers everywhere,
by tempestn 5y ago
From a cloudflare blog post on this, their public DNS resolvers were getting 30x their usual traffic. Presumably that was the case for DNS resolvers everywhere, so that would explain a slowdown:
> But that's not all. Now human behavior and application logic kicks in and causes another exponential effect. A tsunami of additional DNS traffic follows.
> This happened in part because apps won't accept an error for an answer and start retrying, sometimes aggressively, and in part because end-users also won't take an error for an answer and start reloading the pages, or killing and relaunching their apps, sometimes also aggressively.
...
> So now, because Facebook and their sites are so big, we have DNS resolvers worldwide handling 30x more queries than usual and potentially causing latency and timeout issues to other platforms.
https://blog.cloudflare.com/october-2021-facebook-outage/ https://blog.cloudflare.com/october-2021-facebook-outage/
Edit: Although looking at the graph on that page, it appears that only DNS requests for FB properties increased 30x, so that last sentence appears to be misleading. Regardless, a significant overall increase.
- amelius 5y ago> their public DNS resolvers were getting 30x their usual traffic But why does my browser need to do a DNS lookup every time I request a page from HN? It's not like the IP address changes every 5 minutes.
- cortesoft 5y agoBecause hackernews sets their TTL to 5 minutes: dig +noauthority +noquestion +nostats news.ycombinator.com @ns-225.awsdns-28.com. news.ycombinator.com. 300 IN A 209.216.230.240
- lupire 5y agoIt doesn't. But when Facebook DNS is missing, users ask for it many times because they have nothing to cache. This adds load than get block other queries.
- tempestn 5y agoShort answer is because they've set their DNS TTL to 5 minutes: https://mxtoolbox.com/SuperTool.aspx?action=a%3anews.ycombinator.com&run=toolpage https://mxtoolbox.com/SuperTool.aspx?action=a%3anews.ycombin... As for why, you'd have to ask them. It could be to allow for relatively quick DNS failover in the case of an outage. Or if using a proxy like Cloudflare, that provider could prefer short DNS TTLs to have flexibility in their routing.
- deleted 5y ago[deleted]
- ksaj 5y agoCloudflare and similar companies only work if the TTL is very short. If they set it to some infinite number, they wouldn't be do even the most basic load balancing at the global scale in which they operate.