DNS
DNS propagation time: what is really happening?
DNS changes do not travel through the internet as one synchronized global update. The authoritative DNS starts serving the new answer, while recursive resolvers and local caches may keep older answers until their cached time-to-live expires.
The authoritative answer changes first
When you edit a record at the active authoritative DNS provider, those nameservers should begin answering with the new value according to the provider’s update process. If they still return the old record, the problem is not downstream cache expiry yet.
Recursive resolvers keep cached answers until TTL permits refresh
A resolver that cached the old record can continue serving it until the relevant TTL expires. Different users may therefore see different answers for a period after the change.
Lower TTL before a planned cutover
For a predictable migration, reduce the relevant TTL sufficiently ahead of the change so existing long-lived caches have time to expire. After the migration stabilizes, raise the TTL again to a sensible value.
Nameserver changes are a different scope of change
Changing authoritative delegation affects where the entire zone is answered and can involve registry and resolver caching beyond one record. Copy the complete zone and test the new authoritative service before changing nameservers.