Rack::RequestReplication - Replicate Rack app HTTP requests

Replicate requests from one app instance to another. At Springest we used Gor once to test our new Postgres stack vs our at that time current MySQL stack. We replicated all live requests to our staging environment to test new code before it went live. With real traffic!

Unfortunately, we could not test everything we wanted with the setup with Gor. Stuff that relied on sessions (like MySpringest, and course management through our Admin panel) could not be tested properly because the staging environment did not share sessions with the production stack.

Recently, @foxycoder was asked to give a talk about these adventures at Amsterdam.rb. And while we were thinking about all the stuff that we needed to do to get it right with Gor, we came up with the concept of this gem.

This is Rack MiddleWare. And thanks to that, we have all the information and handy tools available to parse and alter request data before we forward it to another stack.

At the moment, it just forwards the request with only a couple of changes:

• The host and/or port to match the stack to forward to.
• The session cookie – it stores a persistent link between the source app's session and the destination app's session in Redis.
• The CSRF token – same as the session, the destination app's authenticity_token is persistent and used in consecutive requests.

It has support for sessions. To make use of it, you need to have Redis running. Redis serves as a key-value store where sessions from the Source App are linked to sessions from the Forward App. This way both apps can have their own session management.

Rails uses a cross site scripting defense mechanism in the form of an authenticity_token parameter. Absense of it, or modifying it between requests results in XSS errors. Therefore we needed to make sure these were properly captured and replaced by the Forwarder before sending the request to the other application.

CSRF tokens are also persisted in Redis and used in consecutive requests, by updating params["authenticity_token"] before handing off the request to the replica app.

Check out the official API docs

Add this line to your application's Gemfile:

gem 'rack-request_replication'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rack-request_replication

require 'sinatra/base'
require 'sinatra/cookies'
require 'rack/request_replication'

class TestApp < Sinatra::Base
  # Forward all requests to another app that runs on localhost, port 4568
  use Rack::RequestReplication::Forwarder,
        host: 'localhost',
        port: 4568,
        session_key: 'rack.session',
        redis: {
          host: 'localhost',
          port: 6379,
          db: 'rack-request-replication'
        }

  get '/' do
    'Hello World'
  end
end

We currently support the following Ruby versions:

• 1.9.3
• 2.1.6
• 2.2.2
• jruby (latest)

Please note that Rubinious is currently not supported.

1. Fork it ( https://github.com/[my-github-username]/rack-request_replication/fork )
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