Prerender Rails

Google, Facebook, Twitter, and Bing are constantly trying to view your website... but Google is the only crawler that executes a meaningful amount of JavaScript and Google even admits that they can execute JavaScript weeks after actually crawling. Prerender allows you to serve the full HTML of your website back to Google and other crawlers so that they don't have to execute any JavaScript. Google recommends using Prerender.io to prevent indexation issues on sites with large amounts of JavaScript.

Prerender is perfect for Angular SEO, React SEO, Vue SEO, and any other JavaScript framework.

This middleware intercepts requests to your Node.js website from crawlers, and then makes a call to the (external) Prerender Service to get the static HTML instead of the JavaScript for that page. That HTML is then returned to the crawler.

Note Make sure you have more than one webserver thread/process running because the prerender service will make a request to your server to render the HTML.

Add this line to your application's Gemfile:

gem 'prerender_rails'

And in config/environment/production.rb, add this line:

	config.middleware.use Rack::Prerender

or if you have an account on prerender.io and want to use your token:

	config.middleware.use Rack::Prerender, prerender_token: 'YOUR_TOKEN'

Note If you're testing locally, you'll need to run the prerender server locally so that it has access to your server.

Testing

When testing make sure you're not using a single threaded application server like default WEBrick one, use Puma or Unicorn to prevent a deadlock when the Prerender Service needs to render your HTML on the fly.

The best way to test the prerendered page is to set the User Agent of your browser to Googlebot's user agent and visit your URL directly. If you View Source on that URL, you should see the static HTML version of the page with the <script> tags removed from the page. If you still see <script> tags then that means the middleware isn't set up properly yet.

Note If you're testing locally, you'll need to run the prerender server locally so that it has access to your server.

How it works

1. The middleware checks to make sure we should show a prerendered page
   1. The middleware checks if the request is from a crawler by checking the user agent string against a default list of crawler user agents
   2. The middleware checks to make sure we aren't requesting a resource (js, css, etc...)
   3. (optional) The middleware checks to make sure the url is in the whitelist
   4. (optional) The middleware checks to make sure the url isn't in the blacklist
2. The middleware makes a GET request to the prerender service(phantomjs server) for the page's prerendered HTML
3. Return that HTML to the crawler

Customization

Whitelist

Whitelist a single url path or multiple url paths. Compares using regex, so be specific when possible. If a whitelist is supplied, only url's containing a whitelist path will be prerendered.

config.middleware.use Rack::Prerender, whitelist: '^/search'

config.middleware.use Rack::Prerender, whitelist: ['/search', '/users/.*/profile']

Blacklist

Blacklist a single url path or multiple url paths. Compares using regex, so be specific when possible. If a blacklist is supplied, all url's will be prerendered except ones containing a blacklist path.

config.middleware.use Rack::Prerender, blacklist: '^/search'

config.middleware.use Rack::Prerender, blacklist: ['/search', '/users/.*/profile']

before_render

This method is intended to be used for caching, but could be used to save analytics or anything else you need to do for each crawler request. If you return a string from before_render, the middleware will serve that to the crawler instead of making a request to the prerender service.

config.middleware.use Rack::Prerender,
	before_render: (Proc.new do |env|
		# do whatever you need to do.
	end)

after_render

This method is intended to be used for caching, but could be used to save analytics or anything else you need to do for each crawler request. This method is a noop and is called after the prerender service returns HTML.

config.middleware.use Rack::Prerender,
	after_render: (Proc.new do |env, response|
		# do whatever you need to do.
	end)

build_rack_response_from_prerender

This method is intended to be used to modify the response before it is sent to the crawler. Use this method to add/remove response headers, or do anything else before the request is sent.

config.middleware.use Rack::Prerender,
	build_rack_response_from_prerender: (Proc.new do |response, prerender_response|
		# response is already populated with the prerender status code, html, and headers
		# prerender_response is the response that came back from the prerender service
	end)

protocol

Option to hard-set the protocol for Prerender accessing your site instead of the middleware figuring out the protocol based on the request.

config.middleware.use Rack::Prerender, protocol: 'https'

Caching

This rails middleware is ready to be used with redis or memcached to return prerendered pages in milliseconds.

When setting up the middleware in config/environment/production.rb, you can add a before_render method and after_render method for caching.

Here's an example testing a local redis cache:

Put this in config/environment/development.rb, and add gem 'redis' to your Gemfile.

require 'redis'
@redis = Redis.new
config.middleware.use Rack::Prerender,
  before_render: (Proc.new do |env|
    @redis.get(Rack::Request.new(env).url)
  end),
  after_render: (Proc.new do |env, response|
    @redis.set(Rack::Request.new(env).url, response.body)
  end)

Using your own prerender service

We host a Prerender server at prerender.io so that you can work on more important things, but if you've deployed the prerender service on your own... set the PRERENDER_SERVICE_URL environment variable so that this middleware points there instead. Otherwise, it will default to the service already deployed by prerender.io.

$ export PRERENDER_SERVICE_URL=<new url>

Or on heroku:

$ heroku config:add PRERENDER_SERVICE_URL=<new url>

As an alternative, you can pass prerender_service_url in the options object during initialization of the middleware

config.middleware.use Rack::Prerender, prerender_service_url: '<new url>'

License

The MIT License (MIT)

Copyright (c) 2013 Todd Hooper <[email protected]>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.