async-websocket

The default Rails server (Puma) uses a thread-per-request model which is unsuitable for large numbers of WebSocket connections. For better scalability, replace Puma with Falcon, which uses a fiber-per-request architecture.

To switch, remove Puma and add Falcon:

$ bundle remove puma
$ bundle add falcon

To execute the project's test suite, use the sus command via bundle exec.

bundle exec sus

Add the async-websocket gem to your project using Bundler to begin using the library for WebSocket client and server implementations.

$ bundle add async-websocket

To improve fiber performance when scaling to a high number of connections, you can tune the Ruby VM environment variables. Note that RUBY_SHARED_FIBER_POOL_FREE_STACKS is an experimental feature available on ruby-head.

Set the following environment variables:

export RUBY_FIBER_VM_STACK_SIZE=0
export RUBY_FIBER_MACHINE_STACK_SIZE=0
export RUBY_SHARED_FIBER_POOL_FREE_STACKS=0

To handle WebSocket connections in a Rails controller, use Async::WebSocket::Adapters::Rails.open(request).

Important: Because WebSocket clients may not send CSRF tokens, you must disable the authenticity token verification for the specific action handling the WebSocket connection using skip_before_action :verify_authenticity_token.

require 'async/websocket/adapters/rails'

class HomeController < ApplicationController
  # WebSocket clients may not send CSRF tokens, so we need to disable this check.
  skip_before_action :verify_authenticity_token, only: [:index]
  
  def index
    self.response = Async::WebSocket::Adapters::Rails.open(request) do |connection|
      message = Protocol::WebSocket::TextMessage.generate({message: "Hello World"})
      connection.write(message)
    end
  end
end

The default Puma server is limited by its thread pool, which can be exhausted by many concurrent WebSocket connections. For high-concurrency WebSocket handling, use Falcon, which utilizes a fiber-per-request architecture.

To switch, remove Puma and add Falcon:

bundle remove puma
bundle add falcon

$ bundle remove puma
$ bundle add falcon

To set up a new project with async-websocket support, create a new Rails application and add the gem via Bundler:

rails new websockets
cd websockets
bundle add async-websocket

$ rails new websockets
$ bundle add async-websocket

If a server advertises HTTP/2 but does not support WebSocket connections over HTTP/2, you can force the client to use HTTP/1.1 by passing alpn_protocols: Async::HTTP::Protocol::HTTP11.names to the Async::HTTP::Endpoint.parse method.

endpoint = Async::HTTP::Endpoint.parse("https://remote-server.com", alpn_protocols: Async::HTTP::Protocol::HTTP11.names)

Async::WebSocket::Client.connect(endpoint) do |connection|
  # ...
end

To integrate async-websocket into a Rails application, add the gem to your bundle using bundle add async-websocket.

$ bundle add async-websocket