Domains, delivery and craft
What is TTL?
How long a DNS record may be cached by resolvers before being fetched again, in seconds. A high TTL means changes propagate slowly; a low one means they propagate fast at the cost of slightly more lookups. It is the control that makes migrations reversible.
Also called: time to live · DNS TTL
How to use it around a change
- Lower the TTL to 300 seconds at least 24 hours before the switch
- Wait for the old, longer TTL to expire everywhere
- Make the change — it now propagates within about five minutes
- Confirm everything works from more than one network
- Raise the TTL back to its normal value once settled
The mistake it prevents
Switching a record with a 24-hour TTL and then discovering a problem. The revert is also cached, so the mistake persists for a day regardless of how fast you notice. Lowering it in advance turns the same error into a five-minute inconvenience.
Not every resolver obeys it
Some ISP resolvers apply their own minimums, so propagation is a distribution rather than a deadline. Plan for a tail of stragglers rather than a clean cutover, and keep the old destination serving until the tail clears.
Where this is covered in depth
A definition can only go so far. Migrating a site without losing what it took years to earn covers this properly — 3 minutes, free, no email required.
Who wrote this
Anas Bin Masud builds e-commerce sites and does technical SEO for businesses in the UK, Canada and Pakistan. These definitions come from client work rather than from a content brief — where an entry describes a mistake, it is usually one found on a real site. More about how I work.