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by JakeTheAndroid 3191 days ago
While DNS caches can sometimes impact DNS updates, we rebuild the entire zone file when a DNS value is updated, and purge the previous cache. Even for customers, this should happen pretty quickly. We maintain a 5 minute TTL on all proxied records internally. So, this happens much faster than most other DNS services.
1 comments
mugsie 3191 days ago
Yeah - that's a pretty standard way of doing things, and thats how DNS servers themselves will operate (mostly) when you make an update to a recordset.

Its not your cache that is the issue.

People have miss behaving caches, that do not always respect TTLs, some apps can cache the DNS response (I remember a Java issue where the initial value found was cached for the lifetime of the process!).

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JakeTheAndroid 3191 days ago
The TTL publicly is static and doesn't matter. The resolver you hit will just point to Cloudflare NS. Why we are faster, is because we point internally, and we don't have misconfigured TTLs or caching (I mean, things happen but it's not common). So once you update the global resolvers your visitors would hit to point to CF, their cache/TTL should never matter since we dictate where our internal DNS points the requested record.
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mugsie 3190 days ago
That is not how resolution works.

What happens is:

#1 - Application (browser, chat client, etc) gets FQDN. It checks if it has the recordset in its cache, and if the TTL is expired.

#2 - Application asks the OS for the recordset. The OS checks its cache, and TTL expiry.

#3 - OS asks the configured local DNS resolvers for the recordset. They check their cache, and TTL expiry.

#4 - These resolvers ask the configured upstream resolvers (e.g. ISP for most home users). They check their cache, and TTL expiry. (This step can repeat, depending on how networks are configured. E.G. ISPs may have DNS resolvers per city, which ask central servers)

#5 - If all of those previous steps fail (the recordset is not cached, or the TTL is expired) the last resolver in the chain will ask the root for the NS records of the zone, which will get fresh records from CloudFlare.

Remember - any of these recursive DNS servers could have an override to cache the recordset for longer than the publicly defined TTL. This is not as much of an issue anymore, but it used to be a massive one.

And this is before applications decide that they know better. - see http://docs.oracle.com/javase/8/docs/technotes/guides/net/pr... (networkaddress.cache.ttl section)

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thinkMOAR 3190 days ago
what mugsie wrote plus.. My post was regarding the management of the zonefile/domain, not so much performance or things related to TTL.

What exactly if your function at CloudFlare Jake? Pondering if this is more marketing then technical/service function. Any chance you are in charge of social media and forum posts about CF?

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ryanlol 3191 days ago
This is a secondary issue. Lots of shitty DNS hosts do not immediately start serving the new records when you push an update.
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