Load Test Your Environment Using em-proxy

With em-proxy, a proxy built with eventmachine, you can send some real traffic to your Engine Yard Cloud environment for load testing. This allows you to test your application’s performance prior to migrating giving you peace of mind that things will perform great once you do migrate. It will also allow you to compare your New Relic stats and make any needed adjustments.

WARNING! Because you will be sending real traffic to Engine Yard Cloud using this technique, you need to be absolutely sure to disable things like email and billing in your application while you test. You do not want to be double billing or spamming your users.

Thoughbot did a great blogpost on their experience using this benchmarking technique. Additionally you can read Igvita’s post on the topic as well.

Using this example configuration, requests returning from Engine Yard Cloud will be dropped at the proxy. This will make your testing completely transparent to your end users.

Configuration and installation

You perform the proxy setup and configuration on your current production servers. It resides between your load balancer and your web server. As a few adjustments will need to be made, we’ll describe those in detail in a moment.

Install the gem and create your configuration file

sudo gem install em-proxy --no-ri --no-rdoc 

Create a proxy.rb file to the root users home directory.

Update Nginx

Since em-proxy will be running on port 80, nginx will have to run on port 8080. Change your nginx vhost listening on port 80 to port 8080, then restart nginx using /etc/init.d/nginx restart command.

Start the proxy

Start the proxy up on one server at a time, if you run into issues along the way it will be much easier to back out any changes.

Run the proxy.rb inside of a screen session.

$ screen 
$ ruby proxy.rb

To detach from the screen session simply hit ctrl+a+d and you will detach.

To later resume the screen session:

$screen -x 

The proxy will start up and start taking traffic on port 80. It will proxy traffic to nginx, locally, on port 8080

Test the setup

Make sure you can curl your app and receive the response you expect.

$ curl -H host:yourhostname.com http://localhost 

Disable the proxy

To turn the proxy off

  1. Kill the Ruby process you fired up.
  2. Revert the nginx config changes so that your vhosts are listening on port 80 instead of port 8080.
  3. Restart Nginx using the command: /etc/init.d/nginx restart

Now you are back to your default configuration.

Example code

An example of proxy.rb

`#` proxy.rb 
require 'em-proxy'

Proxy.start(:host => "", :port => 80) do |conn|
conn.server :production, :host => '', :port => 8080
conn.server :ey_cloud, :host => '', :port => 80
conn.on_data do |data|
conn.on_response do |server, resp|
resp if server == :production

Let’s step through this script and describe what it does.

  1. This starts the proxy up on port 80, and listens for any incoming requests.
    Proxy.start(:host => “”, :port => 80) do |conn|
  2. This proxies the traffic to the servers you define. Your production server proxies locally to nginx and listens on port 8080. NOTE: Replace with the IP of your Engine Yard Cloud environment.
    conn.server :production, :host => ‘’, :port => 8080 
    conn.server :ey_cloud, :host => ‘’, :port => 80
  3. This sends the response back to the user if the traffic came from the production server.
    conn.on_response do |server, resp| 
    resp if server == :production

If you have feedback or questions about this page, add a comment below. If you need help, submit a ticket with Engine Yard Support.


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