Then I have rewritten the CDN as standalone FastCGI server, the cache is directly controlled by the server. If same url is already downloading, then the content is send from the partial downloaded content. I choose monothread to have great performance without thread coherency code (more simple to dev, more eficience if the code is very fast because if the code is very fast most of the time is consumed into thread management and data migration from a CPU to another CPU).
The code is specific, not flexible and generalist. I parse the protocols (DNS, FastCGI, …) on fly. That’s greatly improve the performance, reduce the memory. An internal page is served 3x more faster than a simple « Hello world » into PHP 7.4.
The future improvement are: better cache, cache some stuff where needed (DNS, …), use io_uring to improve file access and be 3x more fast than Nginx with static file, do profile to optimize the code. (And maybe do my own http server)