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Comment by aexaey | Hacker News Reader

> Ycombinator.com, why do you have a TTL of 12 seconds?

You either meant to say 60 seconds, or forgot to factor your local caching DNS resolver in. Here:

  $ dig +short soa ycombinator.com
  ns-225.awsdns-28.com. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400

  $ dig a ycombinator.com @ns-225.awsdns-28.com. | grep -A3 'ANSWER SECTION'
  ;; ANSWER SECTION:
  ycombinator.com.        60      IN      A       54.240.184.14
  ycombinator.com.        60      IN      A       54.240.184.154
  ycombinator.com.        60      IN      A       54.240.184.206

That said, 60 seconds is still ridiculously low.

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Not so for CDN content.

Care to elaborate how/why exactly CDN would be different here?

CDN providers has a highly volatile infrastructure setup, short TTL helps them to dynamically reallocate resources. Just as an example, cache invalidation could be implemented with a switch of DNS records.

>"CDN providers has a highly volatile infrastructure setup"

No they don't. CDNs with the exception of AWS Cloudfront don't run on a cloud provider. Things aren't quickly spun up and down with any kind of velocity. CDNs manage all of their own infrastructure, POPs, hardware etc. There is usually a maximal hardware lifecycle since the CDN business is so CapEx heavy.

Cache-Control TTLs and DNS SOA record TTLs have nothing to do with each other. They are separate layer 7 concerns. The former is used by your browser and the latter by your system's resolver library.

I have never heard of anybody using SOA TTLs records to purge a cache. How would that even work?

CDNs generally give you decent tools to purge your objects.

Source: I worked for a CDN.

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