slowpoke

by ankane

ankane / slowpoke

Rack::Timeout enhancements for Rails

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Slowpoke

Rack::Timeout enhancements for Rails

  • safer service timeouts
  • dynamic timeouts
  • custom error pages

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

Upgrading

0.3.0

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

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

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

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