8.2 Reading an Nginx configuration

By Ravindra Bagale Last updated: 27 September 2026

In short: Nginx configuration is made of directives (name value;) and blocks (name { ... }), also called contexts.

Friends, an Nginx config is made of directives and blocks. Once you understand these four or five directives – listen, server_name, root, index, location – you can read any server block.

मित्रांनो, Nginx कॉन्फिग म्हणजे directives आणि ब्लॉक्स. एकदा हे चार-पाच directives समजले – listen, server_name, root, index, location – की कोणताही server ब्लॉक वाचता येतो.

दोस्तों, Nginx कॉन्फ़िग मतलब directives और ब्लॉक्स. एक बार ये चार-पाँच directives समझ आ गए – listen, server_name, root, index, location – तो कोई भी server ब्लॉक पढ़ सकते हो.

Nginx configuration is made of directives (name value;) and blocks (name { ... }), also called contexts:

main context  (user, worker_processes, error_log)
 ├── events { worker_connections ... }
 └── http {  (mime types, logging, gzip, include conf.d/*.conf)
        └── server {            ← one per website (a "server block")
               listen ...; server_name ...; root ...;
               └── location /path { ... }   ← rules for part of the URL
            }
     }

A fully commented server block:

# /etc/nginx/conf.d/mysite.conf   (Ubuntu: /etc/nginx/sites-available/mysite)
server {
    listen 80;                          # IPv4 port
    listen [::]:80;                     # IPv6 port
    server_name example.com www.example.com;   # which Host names this block answers

    root  /var/www/mysite;              # document root: URL "/" maps here
    index index.html index.htm;         # file served for a folder request

    location / {
        try_files $uri $uri/ =404;      # file? folder? otherwise 404
    }

    location /images/ {
        expires 7d;                     # let browsers cache images for 7 days
    }

    error_page 404 /404.html;           # custom error page (file inside root)
    autoindex off;                      # never list folder contents

    access_log /var/log/nginx/mysite_access.log;
    error_log  /var/log/nginx/mysite_error.log;
}

Directive	What it does	Example
`listen`	Port (and optional IP) to accept connections on; `default_server` makes this the fallback	`listen 80 default_server;`
`server_name`	Names matched against the `Host` header; `_` is a "match nothing" placeholder	`server_name example.com www.example.com;`
`root`	Folder that URL paths are appended to	`root /var/www/mysite;`
`index`	File(s) to try for a folder URL	`index index.html index.php;`
`location`	Rules for matching URL paths	`location /api/ { ... }`
`try_files`	Try files in order, then fall back	`try_files $uri $uri/ /index.html;` (SPA)
`return`	Send a redirect or status immediately	`return 301 https://$host$request_uri;`
`error_page`	Custom error page	`error_page 404 /404.html;`
`client_max_body_size`	Maximum upload size (default 1 MB)	`client_max_body_size 20M;`
`server_tokens`	Show/hide Nginx version in headers and error pages	`server_tokens off;`

The two classic Nginx syntax errors

Every directive ends with a semicolon ;, and every { needs a matching }. sudo nginx -t prints the exact file and line number, e.g. unexpected "}" in /etc/nginx/conf.d/mysite.conf:9. Read it slowly. It is almost always the line before the one reported.

How Nginx chooses the server block

It looks at blocks whose listen matches the port of the request.
Among those, it picks the block whose server_name matches the Host header exactly (then wildcard names like *.example.com).
If nothing matches, it uses the block marked default_server for that port, or the first block loaded if none is marked.

That rule explains the most common complaint: "I configured my site but I still see the welcome page." Some other block won, because it is the default or because your server_name doesn't match what the browser sent.

Ravindra Bagale's Tip

Many students write server_name http://example.com; with http://, and the block never matches. Put only the host name in server_name: server_name example.com www.example.com;. And if the welcome page shows up, first check which block is the default_server.

Ravindra Bagale's Tip – मराठी

खूप students server_name http://example.com; असा http:// सोबत लिहितात, आणि block कधीच match होत नाही. server_name मध्ये फक्त host नाव: server_name example.com www.example.com;. आणि welcome page दिसत असेल तर default_server कोणता block आहे ते आधी बघा.

Ravindra Bagale's Tip – हिंदी

बहुत students server_name http://example.com; ऐसे http:// के साथ लिखते हैं, और block कभी match नहीं होता. server_name में सिर्फ host नाम: server_name example.com www.example.com;. और welcome page दिख रहा हो तो पहले देखो कि default_server कौन सा block है.

Lab

Chala, tumcha server block ughda aani pratyek line samor comment madhe tumchya shabdat arth liha. Mag curl -I -H "Host: example.com" http://localhost aani curl -I http://localhost chalva aani kontya block ne uttar dila te access log madhun shodha.