The Top 25 Nginx Interview Questions To Prepare For

Nginx has become an integral part of modern web development and DevOps stacks. With its high performance stability and rich feature set, Nginx is being used by many top tech companies to serve web content efficiently.

As Nginx usage grows, knowledge of this tool is becoming an increasingly important skill for roles like DevOps engineers, site reliability engineers, backend developers, and system administrators. Interviews for such positions frequently include Nginx-related questions to evaluate the candidate’s expertise.

In this comprehensive guide, I will share the top 25 Nginx interview questions that you must prepare for before your next technical interview Mastering the core concepts, architecture, configuration, and troubleshooting aspects of Nginx will boost your confidence to ace the interview and land your dream job!

1. What is Nginx and what are its key features?

Nginx is a high-performance open source web server known for its speed, scalability, stability, and efficient use of resources. Some of its key features include:

• Event-driven asynchronous architecture – Handles thousands of concurrent connections with minimal resource usage
• Serving static content quickly – Directly delivers static files from disk without processing overhead
• Reverse proxy and load balancing – Distributes requests across multiple backend servers for scalability
• Web acceleration through caching – Caches frequently accessed data to reduce repeated backend calls
• HTTP request processing – Handles GET, POST and streaming requests seamlessly
• TLS/SSL support – Secures connections and data transfer through HTTPS
• Modular architecture – Customizable using third-party modules
• Low memory footprint – Requires less memory than servers like Apache

2. How does Nginx architecture differ from traditional web servers?

Unlike traditional web servers like Apache that use a threaded or process-per-connection architecture, Nginx utilizes an asynchronous, event-driven architecture

In Nginx, a single master process manages multiple worker processes which handle requests. Each worker can handle thousands of concurrent connections efficiently in a non-blocking manner using epoll and kqueue mechanisms. This event-driven approach avoids overhead from thread creation or context switching.

Traditional servers create new processes or threads for every request which consumes substantial resources under high load. Nginx’s architecture makes it highly scalable for modern traffic loads without overburdening the server resources.

3. Explain how Nginx serves static and dynamic content?

For static content like images, CSS, JavaScript files, etc., Nginx simply reads the files from disk and sends them directly to clients. It uses location blocks to map request URIs to corresponding files on disk. This direct serving of static files makes Nginx super-fast.

For dynamic content, Nginx acts as a reverse proxy server. It passes requests to backend application servers like Python/Django, Ruby/Rails, Node.js/Express, etc. to generate the dynamic response. The proxy_pass directive in Nginx specifies these upstream servers. Nginx can load balance requests across multiple app servers for better scalability.

Caching can be implemented on both static and dynamic content using Nginx’s proxy_cache module to reduce duplicate processing.

4. How do you configure Nginx as a load balancer?

To configure Nginx as a load balancer for distributing requests across multiple backend servers, follow these steps:

1. Install Nginx and open the nginx.conf file

2. In the http section, add an upstream block with a name like backend and mention the server addresses:

upstream backend {  server backend1.example.com;   server backend2.example.com;}

1. In the server section, use proxy_pass to route requests to the backend upstream group:

location / {  proxy_pass http://backend; }

1. Optionally add additional parameters like ip_hash for session persistence, keepalive for performance, etc.

2. Save the config file, test it and reload/restart Nginx.

This will make Nginx distribute incoming requests across the two backend servers in a round-robin fashion by default.

5. How does Nginx handle SSL/TLS?

To handle HTTPS requests, Nginx requires an SSL certificate and a private key.

In the Nginx config file, modify the server block for the website to include:

listen 443 ssl; ssl_certificate /path/to/fullchain.pem;ssl_certificate_key /path/to/privkey.pem; 

This specifies that Nginx should listen on port 443 for HTTPS requests. The certificate and key files are provided using the ssl_certificate and ssl_certificate_key directives respectively.

Additional ssl parameters like ssl_protocols and ssl_ciphers can be configured for security. Save the config and reload Nginx to apply changes.

6. Explain how to optimize Nginx performance?

Some ways to optimize Nginx performance include:

• Set optimal worker_processes count to match server CPU cores
• Increase worker_connections limit for more concurrent connections
• Enable keepalive for persistent client connections
• Configure caching for static files and dynamic content
• Enable compression for responses
• Use sendfile for faster file transfers
• Limit request body size to free memory faster
• Upgrade to HTTP/2 for efficient request multiplexing

Careful benchmarking and load testing is required to tune these parameters for maximum performance.

7. How does Nginx handle HTTP caching?

Nginx provides a proxy_cache module for HTTP caching to reduce repeated backend calls for identical requests.

To enable caching, first specify a proxy_cache_path on disk to store cached data. Define caching rules using proxy_cache, proxy_cache_valid, proxy_cache_key etc. in location blocks.

For dynamic content, utilize proxy_cache_background_update to keep cache updated when backend content changes.

The proxy_cache_bypass parameter skips caching for specified request parameters.

Using intelligent caching with optimal expiration policies can significantly improve Nginx performance.

8. How can you use Nginx for rate limiting?

Nginx rate limiting is implemented using the limit_req module. Key steps:

1. Enable limit_req_module in the Nginx config

2. Define a shared memory zone to store state:

limit_req_zone $binary_remote_addr zone=mylimit:10m rate=10r/s;

1. Add limit_req rules to location blocks:

limit_req zone=mylimit;

This allows 10 requests/sec from a client IP. Additional connections are delayed. burst parameter queues excess requests.

Rate limiting prevents abuse and protects backend servers from being overwhelmed with requests.

9. Explain Nginx server block inheritance

Nginx supports inheritance between server blocks using the include directive. This allows you to define common configuration segments in separate files and reuse them across multiple sites.

For example:

# common_config server {  listen 80;  server_name site1.com site2.com;    root /var/www/sites;  index index.htm;  }# site1 configinclude common_config; # additional site1 specific config

When a request for site1.com arrives, it will inherit the common settings like port, document root from the included common_config file. This technique helps avoid duplicating repeating directives.

10. How can you debug problems with an Nginx server?

Key ways to debug Nginx include:

• Check error.log – Detailed errors during processing are logged here
• Access logs – Analyze for trends, spikes, suspicious requests
• Use nginx -t to test config changes
• Enable debug logs at different levels for more verbosity
• Connect a debugger to worker process to intercept errors
• Check metrics like active connections, traffic rate, memory usage
• Use live HTTP request tracing tools like Wireshark
• Test upstream servers’ availability using curl/ping
• Isolate issues step-by-step to narrow down culprit

Carefully analyzing various forensic data allows identifying and fixing problems efficiently.

11. Explain how to manage Nginx cache size and purging?

The proxy_cache_path directive specifies the on-disk cache location and size. The size can be in bytes or you can specify the max number of keys using levels=1:2 format.

When cache disk usage reaches the configured limit, Nginx will automatically delete old cache files based on a Least Recently Used (LRU) algorithm.

Cache can also be purged manually using the PURGE HTTP method against the file’s URL, like:

PURGE /image.jpg

Force