Rack::Timeout enhancements for Rails

• safer service timeouts
• dynamic timeouts
• custom error pages

Add this line to your application’s Gemfile:

gem "slowpoke"

And run:

rails generate slowpoke:install

This creates a public/503.html you can customize.

To try out custom error pages in development, temporarily add to config/environments/development.rb:

config.slowpoke.timeout = 1
config.consider_all_requests_local = false

And add a sleep call to one of your actions:

sleep(2)

The custom error page should appear.

The default timeout is 15 seconds. You can change this in config/environments/production.rb with:

config.slowpoke.timeout = 5

For dynamic timeouts, use:

config.slowpoke.timeout = lambda do |env|
  request = Rack::Request.new(env)
  request.path.start_with?("/admin") ? 15 : 5
end

Subscribe to timeouts with:

ActiveSupport::Notifications.subscribe "timeout.slowpoke" do |name, start, finish, id, payload|
  # report timeout
end

To learn more, see the Rack::Timeout documentation.

Rack::Timeout can raise an exception at any point in the code, which can leave your app in an unclean state. The safest way to recover from a request timeout is to spawn a new process. This is the default behavior for Slowpoke.

For threaded servers like Puma, this means killing all threads when any one of them times out. This can have a significant impact on performance.

You can customize this behavior with:

Slowpoke.on_timeout do |env|
  next if Rails.env.development? || Rails.env.test?

  exception = env["action_dispatch.exception"]
  if exception && exception.backtrace.first.include?("/active_record/")
    Slowpoke.kill
  end
end

Note: To access env["action_dispatch.exception"] in development, temporarily add to config/environments/development.rb:

config.consider_all_requests_local = false

It’s a good idea to set a statement timeout and a connect timeout. For Postgres, your config/database.yml should include something like:

production:
  connect_timeout: 3 # sec
  variables:
    statement_timeout: 5s

If you set the timeout with:

Slowpoke.timeout = 5

Remove it and add to config/environments/production.rb:

config.slowpoke.timeout = 5

If you use migration timeouts, check out this guide for how to configure them directly in config/database.yml.

0.1.0 removes database timeouts, since Rails supports them by default. To restore the previous behavior, use:

production:
  variables:
    statement_timeout: <%= Slowpoke.timeout * 1000 %>

View the changelog

Everyone is encouraged to help improve this project. Here are a few ways you can help:

• Report bugs
• Fix bugs and submit pull requests
• Write, clarify, or fix documentation
• Suggest or add new features

To get started with development:

git clone https://github.com/ankane/slowpoke.git
cd slowpoke
bundle install
bundle exec rake test