Module
Module 5 of 6Lesson 1 of 2~16 min

CDN and caches, fast but sometimes behind

Lesson 1 of the module "Caches, CDN and environments" in the course "Explain how a web product works, from browser to server".

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Lesson objective

By the end of this lesson, you will be able to explain the role of a CDN and of the three cache levels (browser, CDN, server), read a Cache-Control header and propose a way to keep displayed data from going stale.

Where it fits

Caches, CDN and environments

Why is the product fast, why does it sometimes show stale data, and why does a bug only appear in production?

Lessons in this module

  1. CDN and caches, fast but sometimes behind (this lesson)
  2. Local, preview, staging, production

What you will learn in the course

This lesson is part of the course Explain how a web product works, from browser to server

  • Describe the steps of a web request, from the typed address to the displayed page (URL, DNS resolution, encrypted connection, HTTP request and response, browser rendering).
  • Read an HTTP exchange in the browser's Network tab (method, URL, status code, headers, cookies, duration) and draw a first diagnosis from it.
  • Explain how responsibilities are split between browser, frontend, backend, API, database and third-party services, and place where a business rule must run.
  • Explain the role of a CDN and of caches (browser, CDN, server) and anticipate their effects on speed, data freshness and releases.
  • Tell apart local, preview, staging and production environments, and say what changes from one to another (configuration, data, secrets).
  • Place a symptom (slowness, blank page, error, stale data) in the right layer and ask the technical team precise questions.
  • Produce the annotated diagram of a request's journey through your own product and have it validated by a developer.

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