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Architecture Overview

NGINX is a high-performance, event-driven web server and reverse proxy. Understanding its architecture is essential for effective configuration and module development.

Core Design Principles

1. Event-Driven, Non-Blocking

NGINX uses an asynchronous, event-driven model rather than threads:

  • Single thread handles thousands of connections
  • Non-blocking I/O for all operations
  • Minimal memory overhead per connection (~256 bytes)

2. Master/Worker Process Model

┌─────────────────────────────────────────────────────────┐
│                      Master Process                      │
│  • Reads configuration          • Manages workers       │
│  • Binds privileged ports       • Handles signals       │
└─────────────────────────┬───────────────────────────────┘
                          │
        ┌─────────────────┼─────────────────┐
        │                 │                 │
        ▼                 ▼                 ▼
   ┌─────────┐       ┌─────────┐       ┌─────────┐
   │ Worker  │       │ Worker  │       │ Worker  │
   │    1    │       │    2    │       │    N    │
   └─────────┘       └─────────┘       └─────────┘
        │                 │                 │
        └─────────────────┴─────────────────┘
                          │
                    Event Loop
                 (epoll/kqueue)

3. Modular Architecture

Everything in NGINX is a module:

  • Core modules: events, http, stream, mail
  • HTTP modules: proxy, fastcgi, gzip, ssl, rewrite
  • Filter modules: headers, gzip, ssi, charset

Key Sections

Section Description
Process Model Master/worker architecture, signals, graceful reload
Event Loop epoll/kqueue, non-blocking I/O, timers
Request Lifecycle HTTP phases, handlers, filters

Quick Facts

Metric Value
Connections per worker 10,000+ typical
Memory per connection ~256 bytes
Request throughput 100,000+ req/sec
Context switches Minimal (single-threaded)

Learning Path

  1. Process Model - How NGINX manages processes
  2. Event Loop - The heart of NGINX performance
  3. Request Lifecycle - How requests flow through phases
  4. Core APIs - C structures and functions

Further Reading