# Configuration Structure, Contexts and Inheritance — Nginx

Source: https://www.skillbyai.com/en/nginx/f-config

> Read and write NGINX configuration with contexts, directives and includes.

## Directives inside nested contexts

NGINX configuration is a tree of **directives**. Simple directives end with a semicolon (`worker_processes auto;`); **block directives** contain others in braces and are called **contexts**. The main context holds global settings; **`events`** configures connection processing; **`http`** contains everything for HTTP, including **`server`** blocks (virtual hosts) which contain **`location`** blocks (URL-specific rules); **`stream`** handles raw TCP and UDP proxying. Most directives are **inherited** from outer to inner contexts: set `gzip on;` in `http` and every server gets it, unless a server overrides it. A crucial exception to remember: for **array-type directives** such as `add_header` and `proxy_set_header`, defining **any** in an inner context replaces **all** inherited ones, rather than adding to them. **`include`** pulls in other files, keeping configurations modular. Variables such as `$host`, `$uri`, `$remote_addr` and `$request_time` are available in many directives, and **`map`** creates new variables from existing ones.

## A minimal but complete nginx.conf

Main, events, http and one server with locations.

```nginx
user nginx;
worker_processes auto;            # one worker per CPU core
error_log /var/log/nginx/error.log warn;

events {
    worker_connections 4096;      # per worker
}

http {
    include       /etc/nginx/mime.types;
    default_type  application/octet-stream;
    sendfile      on;
    keepalive_timeout 65s;
    gzip          on;             # inherited by every server below

    include /etc/nginx/conf.d/*.conf;

    server {
        listen 80;
        server_name example.com;
        root /var/www/example;

        location / {
            try_files $uri $uri/ =404;
        }
    }
}
```

## add_header in a location wipes inherited headers

If the server block adds security headers and a location adds one `add_header` for caching, that location loses all the server's security headers. Repeat them in that location, ideally by including a shared snippet file.

**Quiz:** Which context contains location blocks?

- [ ] events
- [ ] stream
- [x] server (inside http)
- [ ] main only

*Answer:* server (inside http). Location blocks live inside server blocks within the http context.