DNS
DNS TTL explained: how cache time affects changes
Time to Live is the cache lifetime attached to a DNS answer. A lower TTL can make planned changes become visible to refreshing resolvers sooner, while a higher TTL reduces repeated authoritative queries and keeps stable answers cached longer.
TTL affects caches that fetch the record after the value is set
If a resolver already cached an answer with a long TTL, lowering the TTL at the authoritative server does not retroactively shorten that existing cache. Lower it ahead of a planned move and wait for old caches to expire.
Use low TTL temporarily for high-change windows
Before a controlled migration, a shorter TTL can reduce the period during which users receive the old address. After the destination is stable, return to a normal value rather than leaving every record permanently aggressive.
Rollback also follows cache behaviour
A short TTL helps only resolvers that are allowed to refresh. If you switch back after a failed cutover, some clients may still hold whichever value they cached most recently until that TTL expires.
Nameserver delegation has its own caching considerations
Record TTL planning does not make an authoritative nameserver migration instantaneous. Delegation and nameserver address information can have separate caches, so plan provider moves more carefully than a single A-record change.