Top 40 Nginx Interview Questions and Answers You Must Know

What is Nginx?

Nginx is a lightweight, high‑performance reverse‑proxy web server that supports HTTP, HTTPS, SMTP, POP3 and IMAP, capable of handling tens of thousands of concurrent connections.

Key Advantages of Nginx

Cross‑platform and easy to configure.

Non‑blocking, high‑concurrency handling (2‑5 × 10⁴ connections).

Low memory usage (10 workers use ~150 MB).

Open‑source and cost‑effective.

High stability with rare crashes.

Built‑in health‑check to avoid routing to failed back‑ends.

Typical Use Cases

Standalone HTTP server for static content.

Virtual hosting multiple sites on one machine.

Reverse proxy and load balancing for high‑traffic applications.

API gateway and security management.

How Nginx Processes a Request

server {
    # first server block – independent virtual host
    listen 80;               # listening port
    server_name localhost;   # host name
    location / {
        root html;            # site root directory
        index index.html index.html;
    }
}

On startup Nginx parses the configuration, creates a listening socket, forks worker processes, and each worker accepts connections, registers read/write events, processes the request, and finally closes the connection.

High‑Concurrency Mechanism

Nginx uses an asynchronous, non‑blocking event‑driven model (epoll) so a small number of worker processes can handle a large number of simultaneous connections without allocating a thread per request.

Forward and Reverse Proxy

A forward proxy sits between a client and the origin server, forwarding client requests. A reverse proxy receives external requests and forwards them to internal servers, hiding the origin servers and providing load balancing and security.

Directory Structure

# tree /usr/local/nginx
/usr/local/nginx
├── client_body_temp
├── conf
│   ├── fastcgi.conf
│   ├── mime.types
│   ├── nginx.conf
│   └── ...
├── html
│   ├── 50x.html
│   └── index.html
├── logs
│   ├── access.log
│   └── error.log
├── sbin
│   └── nginx
└── ...

nginx.conf Main Modules

worker_processes 1;
events {
    worker_connections 1024;
}
http {
    include mime.types;
    default_type application/octet-stream;
    sendfile on;
    keepalive_timeout 65;
    server {
        listen 80;
        server_name localhost;
        location / {
            root html;
            index index.html index.htm;
        }
        error_page 500 502 503 504 /50x.html;
        location = /50x.html {
            root html;
        }
    }
    ...
}

Cookie vs Session

Both store key‑value data. Cookies reside on the client browser and are visible to the user; sessions are stored on the server (file, DB, Redis) and can hold sensitive information.

Why Nginx Does Not Use Multithreading

Unlike Apache, which creates a thread or process per request, Nginx handles many requests within a single worker using asynchronous I/O, reducing CPU and memory consumption.

Nginx vs Apache

Lightweight, lower memory footprint.

Asynchronous, better under high concurrency.

Modular design.

Apache uses a synchronous multi‑process model.

Static‑Dynamic Resource Separation

Static files (CSS, JS, images) are served directly by Nginx, while dynamic requests are proxied to application servers such as Tomcat, improving response speed and reducing backend load. CDN can further cache static assets.

Load‑Balancing Algorithms

Round‑robin (default).

Weight‑based.

IP‑hash.

Fair (third‑party module).

URL‑hash (third‑party module).

# round‑robin
upstream backserver {
    server 192.168.0.12;
    server 192.168.0.13;
}

Cross‑Domain Solution

Configure Nginx to proxy cross‑origin API requests through the same origin, eliminating CORS issues.

Virtual Host Configuration

# domain‑based virtual host
server {
    listen 80;
    server_name www.example.com;
    location / {
        root /data/www;
        index index.html;
    }
}
# port‑based virtual host
server {
    listen 8080;
    server_name 8080.example.com;
    location / {
        root /data/www;
        index index.html;
    }
}

Location Directive

The location block matches request URIs and applies specific handling. Examples include exact match, prefix match, case‑sensitive and case‑insensitive regex, and fallback.

# exact match
location = / { return 400; }
# prefix match
location ^~ /av { root /data/av/; }
# regex match
location ~ /media { alias /data/static/; }
# file extension match
location ~* \.(jpg|gif|png|js|css)$ { root /data/av/; }
# default
location / { return 403; }

Rate Limiting

Nginx implements rate limiting using the leaky‑bucket algorithm via ngx_http_limit_req_module and connection limiting via ngx_http_limit_conn_module.

# limit one request per minute per IP
limit_req_zone $binary_remote_addr zone=one:10m rate=1r/m;
server {
    location /seckill.html {
        limit_req zone=one;
        proxy_pass http://backend;
    }
}

Health Check

Backend health can be monitored with the built‑in proxy/upstream modules or the third‑party ngx_http_upstream_check_module.

Compression

Enable gzip to reduce bandwidth for text resources.

http {
    gzip on;
    gzip_min_length 1k;
    gzip_comp_level 2;
    gzip_types text/plain application/javascript text/css;
    gzip_vary on;
}

Other Topics

ngx_http_upstream_module defines server groups for proxy, fastcgi, uwsgi, etc.

C10K problem: handling 10 000 simultaneous sockets.

Gunzip module can decompress upstream responses.

Obtain current time with SSI $date_gmt.

Adding modules requires recompilation.

Set worker_processes to the number of CPU cores for optimal performance.

Common status codes: 499 (client closed), 502 (upstream error), etc.