3 ms·
There is no such thing as DNS propagation, only DNS cache invalidation, and by polling it, you are making your old records stay in more caches and for longer.
by inigyou 4mo ago
There is no such thing as DNS propagation, only DNS cache invalidation, and by polling it, you are making your old records stay in more caches and for longer.
BGP, on the other hand, propagates.
- stavros 4mo agoWhy does the cache mean "nobody requested this in a while, I can drop it" rather than "this may have changed upstream, I'll drop it"?
- processunknown 4mo agoid guess that most resolvers have a least recently used (LRU) policy
- stavros 4mo agoBut they must still have a TTL, they can't just store stale records forever.
- axeldelat 4mo agoYou're right, it's TTL not LRU. The authoritative server publishes a TTL with the record — "you may keep this for N seconds" — and when it's up the resolver has to ask again no matter how popular it is. LRU does show up in resolvers, but as memory management: cache is full, evict the least recently used early. It can only make something disappear sooner than its TTL, never later. It's time-based because there's no back-channel. An authoritative server has no idea who's holding a copy of its records, so it can't push an invalidation.
- stavros 4mo agoYep, that's my mental model as well, thanks.
- inigyou 4mo agoThe server you poll may delegate the request to a server that has the old data in cache. Now the old data is in two caches.
- axeldelat 4mo ago[flagged]