Cianplan

Level 0: Orientation & prerequisites · L0.1 How the internet works & the design interview frame

What happens when you type a URL

Trace a request from browser to database and name each hop.

12 min · Free

What you take away

  • A page load is a chain of hops: DNS lookup, TCP + TLS handshake, load balancer, app server, cache or database, response.
  • DNS answers are cached in the browser, the OS and the resolver, so most requests skip the lookup.
  • The load balancer is the only public front door; app servers and the database sit on a private network.
  • Each hop adds latency, and removing a hop usually beats making one faster.

How the class is laid out

  1. The problem
  2. The simple version
  3. The seven hops
  4. Where the 400 ms go
  5. Check your understanding