TTL (Time to Live) is a value that determines how long a piece of data remains valid before it should be refreshed or discarded. In web technology, TTL appears in multiple contexts: DNS records have TTL values that control how long resolvers cache the record, HTTP cache headers use max-age to specify content freshness, and CDN configurations use TTL to determine how long edge servers cache content.
In DNS, TTL is measured in seconds and tells resolvers how long to cache a DNS response before querying the authoritative server again. A TTL of 3600 means the record is cached for one hour. Lower TTL values enable faster propagation of DNS changes but increase query load on authoritative servers. DNS administration books on Amazon explain TTL strategies.
For URL shortening services, TTL is relevant in several areas. DNS TTL affects how quickly custom domain changes propagate. CDN TTL determines how long cached redirect responses are served from edge servers. Database TTL can be used to automatically expire short URLs after a specified period.
Choosing appropriate TTL values involves balancing freshness against performance. Short TTLs ensure changes propagate quickly but increase origin server load. Long TTLs reduce server load but delay the propagation of updates. Cloud architecture books on Amazon discuss caching strategies.