DNS Propagation (DNS Propagation)
Why DNS Propagation Matters
DNS propagation delays mean that DNS changes are not instant. After updating an A record to point to a new server, some visitors will still reach the old server until their resolver's cache expires. This creates a window where your site behaves differently for different visitors, which complicates server migrations.
The propagation time depends primarily on the TTL of the old cached answer. If the previous TTL was 86400 seconds, a resolver that cached it just before the change can keep that answer for nearly 24 hours. This is why planned migrations often lower the TTL at least one old-TTL interval before changing the record.
Negative caching, operating-system caches, applications, delegation changes, and resolver behavior can extend or alter the transition. There is no universal 48-hour ceiling. During a migration, keep the old and new services available long enough for measured traffic and DNS answers to converge.
How to Check
Use a DNS health checker or propagation checker that queries your DNS from multiple global locations. This shows which resolvers have picked up the new record and which still serve the old one. Comparing results from different regions reveals propagation progress.
Check DNS Health