Glossary term
What is TTL (Time To Live)?
TTL stands for Time To Live.
In DevOps
How long, in seconds, a DNS answer may be cached before resolvers must ask again. 300 = 5 minutes.
Learn it properly · DevOpsLesson 3: DNS Deep Dive: From Domain Name to ServerHow a domain name turns into a server address — records, TTL, Route 53, and the one wildcard record that serves unlimited customer subdomains for a multi-tenant SaaS.In System Design
How long something may be cached or kept before it expires. Example: A DNS answer with TTL 300 can be reused for 5 minutes.
Learn it properly · System DesignLesson 1: What Happens When You Type a URL and Press Enter?The one second between pressing Enter and seeing a page hides a DNS lookup, a trip through a dozen routers, two handshakes and a server doing real work. Every later lesson zooms into one part of that journey.In The Browser Contract
How long a saved DNS answer may be used before the browser must ask again.
Learn it properly · The Browser ContractLesson 0: What Happens When You Type a URL (The Full Version)The full trip from pressing Enter to seeing pixels: DNS, TCP, TLS, HTTP, then reading the page and painting it. Caches skip most steps. Every other lesson in this series fits on this map.In Networking for Developers
A counter in every IP packet that drops by one at each router so lost packets do not travel forever.
Learn it properly · Networking for DevelopersLesson 0: How the Internet Works: Layers, Packets and AddressesThe layer models, what a packet is, MAC, IP and ports, and following one request from your laptop to a server.