What is TTL?
Time-to-Live (TTL) is a value (expressed in seconds) attached to every DNS record. It instructs resolvers, operating systems, and browsers how long they should keep the lookup response in their local cache before asking the authoritative nameserver again.
Caching vs Propagation Delay
A long TTL (e.g. 86400 seconds / 24 hours) reduces server load and speeds up load times for visitors. However, if you update an IP address, resolvers will continue returning the old IP until the 24-hour cache expires. This latency is called DNS propagation delay.
Planning Migration Steps
Before moving server IPs, lower your records' TTLs to 300 seconds (5 minutes) a few days in advance. Once the old TTL expires everywhere, switch the IPs. After verifying the change is stable, restore the TTL to its original long duration.