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Slowpoke

Rack::Timeout enhancements for Rails

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Installation

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.

Development

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.

Production

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.

Safer Service Timeouts

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

Database Timeouts

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

History

View the changelog

Contributing

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

To get started with development:

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