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Rack Canonical Host

Rack middleware that lets you define a single host name as the canonical host for your application. Requests for other host names will then be redirected to the canonical host.

Gem Version Build Status Code Climate


Add this line to your application’s Gemfile:

gem 'rack-canonical-host'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rack-canonical-host


For most applications, you can insert the middleware into the file in the root of the application.

Here’s a simple example of what the in a Rails application might look like after adding the Rack::CanonicalHost middleware.

require 'rack/canonical_host'
require ::File.expand_path('../config/environment',  __FILE__)

use Rack::CanonicalHost, ''
run YourRailsApp::Application

In this case, any requests coming in that aren't for the specified host,, will be redirected, keeping the requested path intact.

Environment-Specific Configuration

You probably don't want your redirect to happen when developing locally. One way to prevent this from happening is to use environment variables in your production environment to set the canonical host name.

With Heroku, you would do this like so:

$ heroku config:add

Then, can configure the middleware like this:

use Rack::CanonicalHost, ENV['CANONICAL_HOST'] if ENV['CANONICAL_HOST']

Now, the middleware will only be used if a canonical host has been defined.


If you’d like the middleware to ignore certain hosts, use the :ignore option, which accepts a string, a regular expression, or an array of either.

use Rack::CanonicalHost, '', ignore: ''

In this case, requests for the host will not be redirected.

Alternatively, you can pass a block whose return value will be used as the canonical host name.

use Rack::CanonicalHost do |env|
  case env['RACK_ENV'].to_sym
    when :staging then ''
    when :production then ''

If you want it to react only on specific hosts within a multi-domain environment, use the :if option, which accepts a string, a regular expression, or an array of either.

use Rack::CanonicalHost, '', if: /.*\.example\.com/
use Rack::CanonicalHost, '', if: /.*\.example\.ru/


To avoid browsers indefinitely caching a 301 redirect, it’s a sensible idea to set an expiry on each redirect, to hedge against the chance you may need to change that redirect in the future.

# Leave caching up to the browser (which could cache it indefinitely):
use Rack::CanonicalHost, ''

# Cache the redirect for up to an hour:
use Rack::CanonicalHost, '', cache_control: 'max-age=3600'

# Prevent caching of redirects:
use Rack::CanonicalHost, '', cache_control: 'no-cache'


  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature.')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request


Thanks to the following people who have contributed patches or helpful suggestions:


Copyright © 2009-2017 Tyler Hunt.

Released under the terms of the MIT license. See LICENSE for details.


Rack middleware for defining a canonical host name.




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