How do I handle authentication in a Plug app?

Use built-in plugs like Plug.BasicAuth for simple HTTP authentication or Plug.Session for session management. For more advanced OAuth or JWT, you'll need to implement custom plugs or integrate third-party libraries, as Plug only provides the middleware foundation.

Should I use Plug or Phoenix for building a web app in Elixir?

Choose Plug for lightweight APIs, microservices, or custom middleware where you need fine-grained control. Opt for Phoenix if you want a full-stack framework with built-in features like Ecto for databases, LiveView for real-time UI, and more extensive tooling.

How to test a Plug router effectively?

Leverage Plug.Test to simulate HTTP requests and assert responses, as shown in the README's testing example. Import Plug.Conn to manipulate connection structs in tests, ensuring your plugs behave correctly under various scenarios.

Does Plug support WebSockets without extra setup?

Yes, Plug v1.14+ includes a native connection upgrade API for WebSockets. Use it with adapters like WebSockAdapter and servers like Bandit, as demonstrated in the websocket example, but note it requires manual routing and handler implementation.

What's the difference between using Cowboy and Bandit with Plug?

Plug.Cowboy uses the stable, Erlang-based Cowboy server, ideal for production environments. Bandit is an Elixir-native alternative that may offer better integration with Elixir's concurrency model; choice depends on your team's familiarity and performance needs.

Open-Awesome

plug

NOASSERTIONElixir

A specification and toolkit for building composable web applications with functions in Elixir.

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What is plug?

Plug is a specification and adapter layer for building web applications in Elixir. It allows developers to compose web request/response pipelines using small, reusable functions called plugs, abstracting away web server details. It serves as the foundational layer for Elixir web frameworks like Phoenix, providing tools for routing, middleware, and connection handling.

Target Audience

Elixir developers building web applications, APIs, or middleware who want a lightweight, composable alternative to full-stack frameworks. It's particularly useful for those creating custom web servers, microservices, or integrating with existing Elixir systems.

Value Proposition

Developers choose Plug for its simplicity, performance, and seamless integration with the Erlang VM. Its functional, composable design allows for flexible middleware pipelines, while its web server abstraction enables running the same application on different servers without code changes.

Overview

Compose web applications with functions

Use Cases

Best For

Building lightweight web APIs in Elixir without a full framework
Creating custom middleware pipelines for HTTP request processing
Developing microservices that need fine-grained control over web server behavior
Prototyping web applications before committing to a larger framework
Adding web interfaces to existing Elixir/OTP applications
Learning how web frameworks like Phoenix work under the hood

Not Ideal For

Teams wanting a full-stack web framework with integrated ORM, templating, and scaffolding tools out of the box
Projects that prioritize rapid prototyping with pre-styled UI components and minimal configuration
Environments where the development team is not already proficient in Elixir and functional programming concepts

Pros & Cons

Pros

Functional Composability

Plugs are simple, chainable functions that enable flexible middleware pipelines, as demonstrated in the router examples where plugs like Plug.Logger can be inserted seamlessly.

Web Server Agnosticism

Plug abstracts web server details, allowing the same application to run on Cowboy or Bandit via connection adapters, giving developers flexibility in deployment.

High-Performance Routing

Plug.Router compiles routes into optimized tree lookups in the Erlang VM, ensuring fast request dispatching without linear overhead.

Rich Middleware Library

Includes ready-to-use plugs for common tasks like authentication, CSRF protection, and static file serving, reducing boilerplate code.

Cons

Minimalist by Design

Lacks higher-level web features such as database integration or templating engines, forcing developers to assemble additional libraries for full-stack development.

Manual Configuration Overhead

Setting up supervision trees, routing, and middleware requires more code and understanding of OTP compared to opinionated frameworks like Phoenix.

Elixir Ecosystem Dependency

Tightly coupled to Elixir and the Erlang VM, making it unsuitable for polyglot projects or teams unfamiliar with functional programming paradigms.

Frequently Asked Questions

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