tachyons/application.amp.erb

## application.amp.erb
<html>
  <head>
    <link rel="canonical" href="<%= current_uri_sans_amp %>">
  </head>
  ...
</html>

## application.html.erb
<html>
  <head>
    <link rel="amphtml" href="/amp<%= current_uri %>">
    <link rel="canonical" href="<%= current_uri %>">
  </head>
  ...
</html>

## application_controller.rb
# app/controllers/application_controller.rb

class ApplicationController < ActionController::Base
  # Prevent CSRF attacks by raising an exception.
  # For APIs, you may want to use :null_session instead.
  protect_from_forgery with: :exception

  before_action :force_amp, if: -> { request.path_parameters[:amp] }

  private

  def force_amp
    request.format = 'amp'
  end
end

## mime_types.rb
# config/initializers/mime_types.rb

Mime::Type.register 'text/html', :amp

## routes.rb
# config/routes.rb

Rails.application.routes.draw do
  scope '(:amp)', constraints: { amp: /amp/ } do
    # Put here all routes that also have AMP variants
    root to: 'home#index'
  end
end
	<html>
	<head>
	<link rel="canonical" href="<%= current_uri_sans_amp %>">
	</head>
	...
	</html>
	<html>
	<head>
	<link rel="amphtml" href="/amp<%= current_uri %>">
	<link rel="canonical" href="<%= current_uri %>">
	</head>
	...
	</html>
	# app/controllers/application_controller.rb

	class ApplicationController < ActionController::Base
	# Prevent CSRF attacks by raising an exception.
	# For APIs, you may want to use :null_session instead.
	protect_from_forgery with: :exception

	before_action :force_amp, if: -> { request.path_parameters[:amp] }

	private

	def force_amp
	request.format = 'amp'
	end
	end
	# config/initializers/mime_types.rb

	Mime::Type.register 'text/html', :amp
	# config/routes.rb

	Rails.application.routes.draw do
	scope '(:amp)', constraints: { amp: /amp/ } do
	# Put here all routes that also have AMP variants
	root to: 'home#index'
	end
	end