Over two decades ago, folks did this using web server paths with index.html prioritized over e.g. index.php or index.cfml or whatever.

When you'd build the page dynamically, you'd also write a static .html before serving the html to the visitor. From then on, the .html got served.

On a new build, you'd rm the .htmls.

Back at the time, it seemed to be "the simplest thing that could possibly work" for multiplying a server's traffic capacity by 10000.