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General Overview

Before we dive into the differences between Apache and Nginx, let’s take a quick look at the background of these two projects and their general characteristics.

Apache

The Apache HTTP Server was created by Robert McCool in 1995 and has been developed under the direction of the Apache Software Foundation since 1999. Since the HTTP web server is the foundation’s original project and is by far their most popular piece of software, it is often referred to simply as “Apache”.

The Apache web server was the most popular server on the internet from at least 1996 through 2016. Because of this popularity, Apache benefits from great documentation and integrated support from other software projects.

Apache is often chosen by administrators for its flexibility, power, and near-universal support. It is extensible through a dynamically loadable module system and can directly serve many scripting languages, such as PHP, without requiring additional software.

Nginx

In 2002, Igor Sysoev began work on Nginx as an answer to the C10K problem, which was an outstanding challenge for web servers to be able to handle ten thousand concurrent connections. Nginx was publicly released in 2004, and met this goal by relying on an asynchronous, events-driven architecture.

Nginx has since surpassed Apache in popularity due to its lightweight footprint and its ability to scale easily on minimal hardware. Nginx excels at serving static content quickly, has its own robust module system, and can proxy dynamic requests off to other software as needed.

Nginx is often selected by administrators for its resource efficiency and responsiveness under load, as well as its straightforward configuration syntax.

Connection Handling Architecture

One difference between Apache and Nginx is the specific way that they handle connections and network traffic. This is perhaps the most significant difference in the way that they respond under load.

Apache

Apache provides a variety of multi-processing modules (Apache calls these MPMs) that dictate how client requests are handled. This allows administrators to configure its connection handling architecture. These are:

• mpm_prefork: This processing module spawns processes with a single thread each to handle requests. Each child can handle a single connection at a time. As long as the number of requests is fewer than the number of processes, this MPM is very fast. However, performance degrades quickly after the requests surpass the number of processes, so this is not a good choice in many scenarios. Each process has a significant impact on RAM consumption, so this MPM is difficult to scale effectively.

• mpm_worker: This module spawns processes that can each manage multiple threads. Each of these threads can handle a single connection. Threads are much more efficient than processes, which means that this MPM scales better than the prefork MPM. Since there are more threads than processes, this also means that new connections can immediately take a free thread instead of having to wait for a free process.

• mpm_event: This module is similar to the worker module in most situations, but is optimized to handle keep-alive connections. When using the worker MPM, a connection will hold a thread regardless of whether a request is actively being made for as long as the connection is kept alive. The event MPM handles keep alive connections by setting aside dedicated threads for handling keep alive connections and passing active requests off to other threads. This keeps the module from getting bogged down by keep-alive requests, allowing for faster execution.

Nginx

Nginx came onto the scene after Apache, with more awareness of the concurrency problems that sites face at scale. As a result, Nginx was designed from the ground up to use an asynchronous, non-blocking, event-driven connection handling algorithm.

Nginx spawns worker processes, each of which can handle thousands of connections. The worker processes accomplish this by implementing a fast looping mechanism that continuously checks for and processes events. Decoupling actual work from connections allows each worker to concern itself with a connection only when a new event has been triggered.

Each of the connections handled by the worker are placed within the event loop. Within the loop, events are processed asynchronously, allowing work to be handled in a non-blocking manner. When a connection closes, it is removed from the loop.

This style of connection processing allows Nginx to scale with limited resources. Since the server is single-threaded and processes are not spawned to handle each new connection, the memory and CPU usage tends to stay relatively consistent, even at times of heavy load.

Static vs Dynamic Content

In terms of real-world use-cases, one of the most common comparisons between Apache and Nginx is the way in which each server handles requests for static and dynamic content.

Apache

Apache servers can handle static content using its conventional file-based methods. The performance of these operations is mainly a function of the MPM methods described above.

Apache can also process dynamic content by embedding a processor of the language in question into each of its worker instances. This allows it to execute dynamic content within the web server itself without having to rely on external components. These dynamic processors can be enabled through the use of dynamically loadable modules.

Nginx

Nginx does not have any ability to process dynamic content natively. To handle PHP and other requests for dynamic content, Nginx has to hand off a request to an external library for execution and wait for output to be returned. The results can then be relayed to the client.

These requests must be exchanged by Nginx and the external library using one of the protocols that Nginx knows how to speak (http, FastCGI, SCGI, uWSGI, memcache). In practice, PHP-FPM, a FastCGI implementation, is usually a drop-in solution, but Nginx is not as closely coupled with any particular language in practice.

Distributed vs Centralized Configuration

Apache and Nginx differ significantly in their approach to allowing overrides on a per-directory basis.

Apache

Apache includes an option to allow additional configuration on a per-directory basis by inspecting and interpreting directives in hidden files within the content directories themselves. These files are known as .htaccess files.

Since these files reside within the content directories themselves, when handling a request, Apache checks each component of the path to the requested file for an .htaccess file and applies the directives found within. This effectively allows decentralized configuration of the web server, which is often used for implementing URL rewrites, access restrictions, authorization and authentication, even caching policies.

Nginx

Nginx does not interpret .htaccess files, nor does it provide any mechanism for evaluating per-directory configuration outside of the main configuration file. Apache was originally developed at a time when it was advantageous to run many heterogeneous web deployments side-by-side on a single server, and delegating permissions made sense. Nginx was developed at a time when individual deployments were more likely to be containerized and to ship with their own network configurations, minimizing this need. This may be less flexible in some circumstances than the Apache model, but it does have its own advantages.

Using Apache and Nginx Together

After reviewing

the benefits and limitations of both Apache and Nginx, you may have a better idea of which server is more suited to your needs. In some cases, it is possible to leverage each server’s strengths by using them together.

The conventional configuration for this partnership is to place Nginx in front of Apache as a reverse proxy. This will allow Nginx to handle all client requests. This takes advantage of Nginx’s fast processing speed and ability to handle large numbers of connections concurrently.

For static content, which Nginx excels at, files or other directives will be served quickly and directly to the client. For dynamic content, for instance PHP files, Nginx will proxy the request to Apache, which can then process the results and return the rendered page. Nginx can then pass the content back to the client.

This setup works well for many people because it allows Nginx to function as a sorting machine. It will handle all requests it can and pass on the ones that it has no native ability to serve. By cutting down on the requests the Apache server is asked to handle, we can alleviate some of the blocking that occurs when an Apache process or thread is occupied.

This configuration also facilitates horizontal scaling by adding additional backend servers as necessary. Nginx can be configured to pass requests to multiple servers, increasing this configuration’s performance.

Conclusion

Both Apache and Nginx are powerful, flexible, and capable. Deciding which server is best for you is largely a function of evaluating your specific requirements and testing with the patterns that you expect to see.

There are differences between these projects that have a very real impact on the raw performance, capabilities, and the implementation time necessary to use either solution in production. Use the solution that best aligns with your objectives.

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