How Nginx Handles Requests: A Deep Dive into Its Event Loop Lifecycle

A detailed technical reference published on DEV Community breaks down the complete lifecycle of an nginx event loop, tracing every step from a TCP packet arriving at the network interface card to the response being sent back to the client. The guide covers core Linux concepts such as file descriptors, kernel socket structures, and DMA-based memory transfers, explaining how the CPU is largely bypassed during packet reception. Using two concurrent users as a running example, it walks through nginx startup, worker process behavior, and how epoll enables efficient I/O waiting. The reference also catalogs all relevant system calls, kernel buffers, and failure modes in dedicated master sections. It is intended as a precise, bottom-up resource for engineers seeking to understand nginx internals at the operating system level.