A complete guide to HTTP caching

Caching is the invisible backbone of the web. It’s what makes sites feel fast, reliable, and affordable to run. Done well, it slashes latency, reduces server load, and allows even fragile infrastructure to withstand sudden spikes in demand. Done poorly – or ignored entirely – it leaves websites slow, fragile, and expensive.

At its core, caching is about reducing unnecessary work. Every time a browser, CDN, or proxy has to ask your server for a resource that hasn’t changed, you’ve wasted time and bandwidth. Every time your server has to rebuild or re-serve identical content, you’ve added load and cost. Under heavy traffic – whether that’s Black Friday, a viral news story, or a DDoS attack – those mistakes compound until the whole stack buckles.

And yet, despite being so fundamental, caching is one of the most misunderstood aspects of web performance.

Source: A complete guide to HTTP caching – Jono Alderson