Why Nginx is so fast?

The question is intentionally formulated in an oversimplified way. This is what you might hear from your boss or client—let us migrate from old technologies to Nginx because it will make our website faster and users happier. The migration process is described in thousands of online articles and even some books, and we will not write about it here. Many of our readers have probably gone down that path several times and know the facts: first, it is usually true that websites get faster and second, no, it is not usually a full migration. You will rarely dispose of Apache completely and plug Nginx in its place. Although this "total conversion" also happens, most of the time you start with inserting Nginx between Apache and the Internet. To understand why this is okay, why this helps at all, and how to move forward from there, read on.

To describe the main conceptual change that is implemented by using Nginx as a reverse proxy we will use, for simplicity...