Every few years, a technology appears that is sold as universal site acceleration. Now it is the edge — the return of content and part of the calculations from the nodes scattered closer to the visitor. The mechanism works, it is described in detail in the Cloudflare and Vercel documentation, and in certain tasks the difference is visible to the naked eye.
The problem starts where edge is offered instead of engineering. The business pays for the migration, and the site slows down for a reason that the distributed network does not touch at all. Below I will analyze what the delay consists of, what edge removes from it, what remains in place, and how to check your own site in half an hour without a contractor.
What is the pause between the click and the content
The time from the click to the appearance of the text is the sum of several independent terms.
Network. The signal goes to the server and back. Kyiv — Frankfurt is tens of milliseconds, Kyiv — Virginia already hundreds. The delay of the radio channel is on top of the mobile, so the same site from home Wi-Fi and from 4G in the subway feels different.
Server. How long does it take to compile HTML: requests to the database, PHP version, nginx settings, page cache availability. This part is visible as TTFB - time to first byte.
Browser. Document weight, scripts, fonts, images. Even when the first byte arrived in 150ms, the first screen can still be a second away if there are a hundred or so pictures hanging in the cap without delayed loading.
Edge works with the first application and, if cached, with the second. He does not touch the third.
What a distributed network really pulls off
The first is physical distance. If the audience is in Poland, Germany or the USA, and the server is in Kyiv, each request pays for the round trip. A node in the visitor region shortens this path, and it is not a matter of faith: the difference is visible in the same TTFB taken from different locations.
The second is the load on the source. The cached page is provided by the node, your server does not see it. At traffic peaks, this saves from falling, because some requests simply do not reach the backend.
The third is static. Images, CSS, fonts live well at the edge of the network: they are given compressed, converted to modern formats on the fly, cached for a long time. This is the cheapest and most predictable part of the effect.
What edge doesn't do
Here begins the honest part, which is usually absent in presentations.
Dynamics are not cached. Cart, checkout, personal account, personal prices for the wholesaler — all this is recalculated every time. A node can close a connection, but cannot give away someone else's cart from the cache. If your checkout is slow, it will stay that way.
