HowToCodePage

CDNs & Caching

Serving fast from an edge near the visitor.

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This course has 3 lessons. Start with the first one and use the next / previous links at the bottom of each lesson — the sidebar keeps the whole course in order.

Lessons

  1. How a CDN serves your contentEdge locations, cache hits and misses, origin shielding, and how to tell which layer answered a request.
  2. Cache headers and cache keysThe headers that decide how long the edge holds a copy, and what makes two requests share one entry.
  3. Invalidation, purging and what not to cacheHow to retire a cached copy quickly, why fingerprinted URLs beat purging, and the responses that must never be stored.

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Last refreshed 2026-09-17.