Cowboy vs Gunicorn: What are the differences?

**Introduction:**
Cowboy and Gunicorn are both popular web servers for serving Python applications. Here are some key differences between them:

**1. Concurrency Models:**
Cowboy utilizes a lightweight event-driven model with asynchronous I/O while Gunicorn uses a pre-fork worker model. This means Cowboy is more suitable for handling long-lived connections and high concurrent loads, while Gunicorn may be more efficient for short-lived connections and CPU-bound applications.

**2. Language Support:**
Cowboy is primarily designed to work with Erlang applications, providing native support for Erlang/OTP features. On the other hand, Gunicorn is specifically tailored for serving WSGI applications in Python, making it an ideal choice for Python developers.

**3. Configuration Options:**
Gunicorn offers a wide range of configuration options that can be customized to fine-tune the server behavior according to specific application requirements. Cowboy, on the other hand, has a simpler configuration setup that may lack the same level of flexibility for certain use cases.

**4. Middleware Support:**
Gunicorn allows for the integration of middleware components to enhance the functionality of the server, enabling features like request/response modification, authentication, and more. Cowboy, while supporting middleware, may not offer the same extensive library of middleware options as Gunicorn.

**5. Deployment Strategy:**
When it comes to deployment, Gunicorn is commonly used in combination with a reverse proxy server like Nginx or Apache to handle tasks such as load balancing and SSL termination. Cowboy, being part of the Erlang ecosystem, is typically used within an Erlang clustering setup for fault tolerance and scalability.

**6. Performance Characteristics:**
Due to its event-driven architecture, Cowboy tends to have better performance in handling a large number of concurrent connections compared to Gunicorn, especially for scenarios where long-polling or WebSocket connections are prevalent. Gunicorn, with its pre-fork worker model, excels in scenarios with a moderate number of worker processes handling requests in a more traditional manner.

In Summary, Cowboy and Gunicorn differ in their concurrency models, language support, configuration options, middleware support, deployment strategy, and performance characteristics, making them suitable for distinct use cases within the realm of web server technologies.