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"A dizzying lifetime... reeling by on celluloid" -- Rush / Between The Wheels

Reel is a fast, non-blocking "evented" web server built on http_parser.rb, websocket_parser, Celluloid::IO, and nio4r. Thanks to Celluloid, Reel also works great for multithreaded applications and provides traditional multithreaded blocking I/O support too.

Connections to Reel can be either non-blocking and handled entirely within the Reel::Server thread (handling HTTP, HTTPS, or UNIX sockets), or the same connections can be dispatched to worker threads where they will perform ordinary blocking IO. Reel provides no built-in thread pool, however you can build one yourself using Celluloid.pool, or because Celluloid already pools threads to begin with, you can simply use an actor per connection.

This gives you the best of both worlds: non-blocking I/O for when you're primarily I/O bound, and threads for where you're compute bound.

Is it any good?


Here's a "hello world" web server benchmark, run on a 2GHz i7 (OS X 10.7.3). All servers used in a single-threaded mode.

Reel performance on various Ruby VMs:

# httperf --num-conns=50 --num-calls=1000

Ruby Version        Throughput    Latency
------------        ----------    -------
JRuby 1.7.0         3978 req/s    (0.3 ms/req)
rbx HEAD            2288 reqs/s   (0.4 ms/req)
Ruby 1.9.3          2071 req/s    (0.5 ms/req)

Comparison with other web servers:

Web Server          Throughput    Latency
----------          ----------    -------
Goliath (0.9.4)     2058 reqs/s   (0.5 ms/req)
Thin    (1.2.11)    7502 reqs/s   (0.1 ms/req)
Node.js (0.6.5)     11735 reqs/s  (0.1 ms/req)

All Ruby benchmarks done on Ruby 1.9.3. Latencies given are average-per-request and are not amortized across all concurrent requests.


Please see the Reel Wiki for detailed documentation and usage notes.

YARD documentation is also available.

Framework Adapters


A Rack adapter for Reel is available at:


The most notable library with native Reel support is webmachine-ruby, an advanced HTTP framework for Ruby with a complete state machine for proper processing of HTTP/1.1 requests. Together with Reel, Webmachine provides full streaming support for both requests and responses.

To use Reel with Webmachine, add the following to your Gemfile:

gem 'webmachine', git: 'git://'

Then use config.adapter = :Reel when configuring a Webmachine app, e.g:

MyApp = do |app|
  app.routes do
    add ['*'], MyHome

  app.configure do |config|
    config.ip      = MYAPP_IP
    config.port    = MYAPP_PORT
    config.adapter = :Reel

    # Optional: handler for incoming websockets
    config.adapter_options[:websocket_handler] = proc do |websocket|
      # websocket is a Reel::WebSocket
      websocket << "hello, world"

See the Webmachine documentation for further information

Ruby API

Reel aims to provide a "bare metal" API that other frameworks (such as Rack and Webmachine) can leverage. This API can also be nice in performance critical applications.

Block Form

Reel lets you pass a block to initialize which receives connections:

require 'reel'

Reel::Server::HTTP.supervise("", 3000) do |connection|
  # Support multiple keep-alive requests per connection
  connection.each_request do |request|
    # WebSocket support
    if request.websocket?
      puts "Client made a WebSocket request to: #{request.url}"
      websocket = request.websocket

      websocket << "Hello everyone out there in WebSocket land"
      puts "Client requested: #{request.method} #{request.url}"
      request.respond :ok, "Hello, world!"


When we read a request from the incoming connection, we'll either get back a Reel::Request object, indicating a normal HTTP connection, or a Reel::WebSocket object for WebSockets connections.

Subclass Form

You can also subclass Reel, which allows additional customizations:

require 'reel'

class MyServer < Reel::Server::HTTP
  def initialize(host = "", port = 3000)
    super(host, port, &method(:on_connection))

  def on_connection(connection)
    connection.each_request do |request|
      if request.websocket?

  def handle_request(request)
    request.respond :ok, "Hello, world!"

  def handle_websocket(sock)
    sock << "Hello everyone out there in WebSocket land!"


  • Fork this repository on github
  • Make your changes and send me a pull request
  • If I like them I'll merge them
  • If I've accepted a patch, feel free to ask for commit access


Copyright (c) 2012 Tony Arcieri. Distributed under the MIT License. See LICENSE.txt for further details.