cache

A cache is a copy of something, kept somewhere fast to reach, so the same work does not have to happen again. In web hosting, it usually means a copy of a page or an image, stored at a data centre close to the visitor, ready to be handed over the instant it is asked for, instead of being rebuilt or pulled from further away each time.

Think of it as the difference between answering a question from memory and looking it up again from scratch every single time someone asks. If the answer has not changed, there is no reason to redo the work.

For a static site, most pages are close to ideal candidates for this, because the file that gets served is the same for every visitor until the next deploy changes it.

Why it matters to you

Caching is one of the biggest reasons a site served from a CDN feels instant. Instead of every visitor’s request travelling all the way to wherever the page was originally built and waiting for it to be assembled, the nearby the edge location has already got a copy ready, and hands it over immediately.

It also reduces load on the systems that build the page in the first place. If ten thousand people ask for the same page in an hour, a well cached setup answers most of those from stored copies, rather than doing the same work ten thousand times.

How I set it up

Because the sites I build are static files, most pages are cached aggressively at the edge by default, with rules that say how long a copy is considered fresh before checking for a newer one. When I deploy a change, that deploy also tells the network the old cached copies are no longer valid, so visitors get the new version right away instead of waiting for a cache to expire on its own.

I am careful about what does and does not get cached this way. A page that is the same for everyone is a good candidate. Something that depends on who is asking, such as a logged-in area, is handled differently, so a cache never accidentally shows one visitor’s information to another.

What it looks like in practice

Caching is invisible when it works, which is most of the time. A visitor loads a page and it appears immediately, whether they are the first person to view it that day or the ten-thousandth. If I make a change and deploy it, that change is live everywhere within a couple of minutes, without anyone needing to manually clear anything or wait out an old cached copy.