Why changes take time.
WHAT A RESOLVER IS
The service your device asks when it needs to find a domain. Usually provided by your internet provider, or a public resolver.
CACHING
Resolvers remember answers for a period, so they do not ask again for every request.
That period is the TTL, set on each record.
WHY THIS CAUSES CONFUSION
After changing a record, resolvers holding the old answer continue serving it until their copy expires.
Different resolvers expire at different moments, so some people see the new value and others do not.
That is normal and it resolves itself.
WHAT PROPAGATION ACTUALLY IS
Not a push. Nothing is being distributed anywhere.
It is simply old cached copies expiring at different times around the world.
HOW LONG
Up to the TTL, and in practice usually less.
Some resolvers ignore short TTLs and cache longer, which is why the occasional person sees the old value well after everyone else.
WHAT YOU CAN DO
Lower the TTL in advance of a planned change. Then the old answer expires quickly.
