A lean and simple Rack middleware that 301 redirects requests from one host to another.

This is useful for environments where it's difficult or impossible to implement this via Nginx/Apache configuration (e.g. Heroku.)

I'm using this to redirect traffic from a *.herokuapp.com subdomain to a custom domain, and to redirect the www subdomain to the bare domain.

Configuration below is for Rails, but this middleware should also work just fine with Sinatra and bare Rack apps.

in Gemfile:

gem 'rack-host-redirect'

in config/environments/production.rb:

config.middleware.use Rack::HostRedirect, {
  'myapp.herokuapp.com' => 'www.myapp.com'
}

With this configuration, all requests to myapp.herokuapp.com will be 301 redirected to www.myapp.com.

Path, querystring and protocol are preserved, so a request to:

https://myapp.herokuapp.com/foo?bar=baz

will be 301 redirected to:

https://www.myapp.com/foo?bar=baz

Addtional host redirections can be specified as key-value pairs in the host mapping hash:

config.middleware.use Rack::HostRedirect, {
  'myapp.herokuapp.com' => 'www.myapp.com',
  'old.myapp.com'       => 'new.myapp.com'
}

Multiple hosts that map to the same redirect destination host can be specified by an Array key:

config.middleware.use Rack::HostRedirect, {
  %w(myapp.herokuapp.com foo.myapp.com) => 'www.myapp.com'
}

URI methods to set for redirect location can be specified as a hash value:

# Don't preserve path or query on redirect:
config.middleware.use Rack::HostRedirect, {
  'bar.myapp.com' => {host: 'www.myapp.com', path: '/', query: nil}
}

When specifying a URI methods hash, the :host key is required; all other URI keys are optional.

When you specify a host redirect, it will redirect all requests to that host, but if you need certain exclusions to this -- e.g. you're handling a Let's Encrypt challenge request in your app, so you need to let that pass through -- you can do so via passing in a Proc to the :exclude key:

# Allow ACME challenge request to pass through, redirect everything else:
config.middleware.use Rack::HostRedirect, {
  'www.example.com' => {
    host: 'example.com', 
    exclude: -> (request) { request.path.start_with?('/.well-known/acme-challenge/') }
  }
}

The proc will be called for each request with the Rack::Request object. If the proc returns a truthy value, the request will pass through without a redirect.

If your app is setting config.force_ssl = true and you're redirecting from a domain for which you don't maintain certs, you should insert Rack::HostRedirect ahead of ActionDispatch::SSL in the middleware stack, so that the redirect happens before the SSL upgrade:

config.middleware.insert_before ActionDispatch::SSL, Rack::HostRedirect, {
  'www.legacy-domain.com' => 'www.myapp.com'
}