Bandit

Bandit is an HTTP server for Plug apps.

Bandit is written entirely in Elixir and is built atop Thousand Island. It can serve HTTP/1.x and HTTP/2 clients over both HTTP and HTTPS. It is written with correctness, clarity & performance as fundamental goals. It was introduced at ElixirConf 2021.

In recent performance tests, Bandit's HTTP/1.x engine is up to 5x faster than Cowboy depending on the number of concurrent requests. When comparing HTTP/2 performance, Bandit is up to 2.3x faster than Cowboy (this number is likely even higher, as Cowboy was unable to complete many test runs without error). This is possible because Bandit has been built from the ground up for use with Plug applications; this focus pays dividends in both performance and also in the approachability of the code base.

Bandit also emphasizes correctness. Its HTTP/2 implementation scores 100% on the h2spec suite in strict mode. Extensive units tests (90%+ coverage for all non-legacy modules), credo analysis and dialyzer coverage round out a test suite that ensures that Bandit is and will remain a platform you can count on.

Lastly, Bandit exists to demystify the lower layers of infrastructure code. In a world where The New Thing is nearly always adding abstraction on top of abstraction, it's important to have foundational work that is approachable & understandable by users above it in the stack.

Project Goals

• Implement comprehensive support for HTTP/1.0 through HTTP/2 (and beyond) backed by obsessive RFC literacy and automated conformance testing
• Aim for minimal internal policy and HTTP-level configuration. Delegate to Plug as much as possible, and only interpret requests to the extent necessary to safely manage a connection & fulfill the requirements of supporting Plug
• Prioritize (in order): correctness, clarity, performance. Seek to remove the mystery of infrastructure code by being approachable and easy to understand
• Become the go-to HTTP & low-level networking stack of choice for the Elixir community by being reliable, efficient, and approachable

Project Status

Bandit is still a young project, and much work remains before it is ready for production use. That having been said, much progress has been made already. The project is progressing steadily towards full Phoenix support, with a phased development plan focusing on one major set of features at a time.

As of the current 0.5.x release series, Bandit features the following:

• Complete support for running HTTP(S) Phoenix applications which do not make use of WebSockets
• Complete support of the Plug API
• Complete server support for HTTP/2 as defined in RFC 7540, comprehensively covered by automated h2spec conformance testing
• Complete server support for HTTP/1.x as defined in RFC 2616
• Extremely scalable and performant client handling at a rate up to 5x that of Cowboy for the same workload with as-good-or-better memory use

Today, any HTTP(S)-only Phoenix app or Plug app should work with Bandit as a drop-in replacement for Cowboy. The roadmap to full Phoenix support and an eventual 1.0 release looks more or less like the following:

• [x] 0.1.x series: Proof of concept (along with Thousand Island) sufficient to support HAP
• [x] 0.2.x series: Revise process model to accommodate forthcoming HTTP/2 and WebSocket adapters
• [x] 0.3.x series: Implement HTTP/2 adapter
• [x] 0.4.x series: Re-implement HTTP/1.x adapter
• [ ] 0.5.x series: Implement WebSocket extension
• [ ] 0.6.x series: Enhance startup options, complete & revise documentation & tests
• [ ] 0.7.x series: Bugfixes from a wider release to ensure a solid 1.0

Using Bandit With Phoenix

As of the 0.5.x branch Bandit supports Phoenix applications which use HTTP(S). Phoenix applications which use WebSockets for features such as Channels or LiveView are not yet supported (though this support is coming soon!).

That having been said, using Bandit to host your Phoenix application couldn't be simpler:

1. Add Bandit as a dependency in your Phoenix application's mix.exs:

   {:bandit, ">= 0.5.0"}
   

2. Add the following to your endpoint configuration in config/config.exs:

   config :your_app, YourAppWeb.Endpoint,
     adapter: Bandit.PhoenixAdapter
   

3. That's it! You should now see messages at startup indicating that Phoenix is using Bandit to serve your endpoint.

Using Bandit With Plug Applications

Using Bandit to host your own Plug is very straightforward. Assuming you have a Plug module implemented already, you can host it within Bandit by adding something similar to the following to your application's Application.start/2 function:

Usage of Bandit is very straightforward. Assuming you have a Plug module implemented already, you can host it within Bandit by adding something similar to the following to your application's Application.start/2 function:

def start(_type, _args) do
  children = [
    {Bandit, plug: MyApp.MyPlug, scheme: :http, options: [port: 4000]}
  ]

  opts = [strategy: :one_for_one, name: MyApp.Supervisor]
  Supervisor.start_link(children, opts)
end

Bandit takes a number of options at startup, which are described in detail in the Bandit documentation.

For less formal usage, you can also start Bandit using the same configuration options via the Bandit.start_link/1 function:

# Start an http server on the default port 4000, serving MyApp.MyPlug
Bandit.start_link(plug: MyApp.MyPlug)

Implementation Details

Bandit's HTTP/2 implementation is described in detail in its own README. Similar documentation for the HTTP/1.x implementation is a work in progress.

Contributing

Contributions to Bandit are very much welcome! Before undertaking any substantial work, please open an issue on the project to discuss ideas and planned approaches so we can ensure we keep progress moving in the same direction.

All contributors must agree and adhere to the project's Code of Conduct.

Security disclosures should be sent privately to [email protected].

Installation

Bandit is available in Hex. The package can be installed by adding bandit to your list of dependencies in mix.exs:

def deps do
  [
    {:bandit, ">= 0.5.0"}
  ]
end

Documentation can be found at https://hexdocs.pm/bandit.

License

MIT