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Deathstare is a set of tools for load-testing JSON REST APIs. It provides a JSON REST API client with a promise styled approach to dependent concurrent operations, a Rails engine-based web dashboard, auto-scaling test workers on Heroku, and streaming results to/from Librato.

Build Status


The reason we created Deathstare is that when we went looking for custom DDOS tools, we found that they all provided a way to hammer on a web site with lots of GET requests. However, our intended target was not a web site, but a web-based API.

To this end, we built a set of tools that allowed us to create detailed, application-specific performance test suites that can be scaled up to a very large number of parallel requests.


  • Heroku APP ID

  • Redis server

      Failing to have a Redis server running locally (during development) or on Heroku (once deployed there)
      will generate errors in the application log and will generate Exceptions to the UI.
  • Librato Account to gather stats

      Failing to have a Librato account, or not setting up the environment variables LIBRATO_EMAIL and LIBRATO_API_TOKEN
      will generate an Exception to remind you to set that up.

Getting started

All of the needed set up is done in your own project, for now we recommend starting with a newly generated Rails app.

Add deathstare to your Gemfile:

gem 'deathstare', git: ''

You will need to include the following lines in the Gemfile of your testing application since gemspec cannot
specify a git resource until Heroku merges our pull request

    # required for app identification to work correctly
    gem 'omniauth-heroku', git: '', branch: 'report_uid_and_extra_params', ref: 'c1250900744ba96993f49926f2c4021d735aef8e'

Mount the engine in config/routes.rb:

MyApp::Application.routes.draw do
  mount Deathstare::Engine => '/'

And configure it in an initializer, e.g. config/initializers/deathstare.rb:

Deathstare.configure do
  config.heroku_app_id       = 'Your Heroku App ID'
  config.heroku_oauth_id     = 'Your Heroku OAuth ID'
  config.heroku_oauth_secret = 'Your Heroku OAuth secret'
  config.librato_email       = 'Your Librato email address'
  config.librato_api_token   = 'Your Librato API token'
  config.target_urls << ''
  config.target_urls << ''

Install deathstare and run the migrations:

bundle install
rake deathstare:install:migrations
rake db:create
rake db:migrate

It's now possible to start the dashboard:

rails server

Create a suite directory and populate it with subclasses of {Deathstare::Suite}. These are your test suites! You can run them with rake or in the web dashboard. To see a list of suites runnable with rake:

rake -T suite:

To view this documentation locally in your browser, with the dashboard running:

rake deathstare:yard
open http://localhost:3000/doc

To scale your tests up using parallel workers, you need to deploy your application to Heroku. This is left as an exercise for the reader.


Running Specs

First, put your database configuration in spec/dummy/config/database.yml.

Then run the specs as usual:

rake spec

You can view the coverage report as well.

open coverage/index.html

Updating The Spec Database

In order to update the spec database when you add a migration, you'll need to add the migration to the dummy app and migrate it.

To avoid errors migrating from the root directory, go into the dummy app and migrate there. For more info see rails/rails#10952

rake app:deathstare:install:migrations
cd spec/dummy
rake db:migrate

Writing Performance Tests

In the suite directory, create a subclass of Deathstare::Suite and use the test method to create test cases. In the body of each test you have your own Device, logged in and ready to use, and helper methods from SuiteHelper.

As an example:

class MyWidgetSuite < Deathstare::Suite
  test "get a widget" do |device|
    # Each test iteration gets a new logged-in device.
    # You can perform requests using the device to get a promise for a result.
    # Session information is sent automatically with each request.
    device.get("/api/widgets/1").then do |result|
      # Call then on the promise to provide a callback that processes the result.
      # You can make additional API calls on the device inside a callback.
      puts "widget is named #{result[:response][:name]}"
      device.patch("/api/widgets/1", {name:"frank"})

  test "post a widget" do |device|"/api/widgets", {name:"ralph"}).then do |result|
      puts "Got message: #{result[:response][:messages].join}"
      # You must return either a result or another promise,
      # in this case we'll just return the original result.

Always return either a valid result OR a dependent request promise in promise callbacks. This is necessary to properly construct the request chain. Keep in mind that Ruby blocks will automatically return the last evaluated value.

Never use instance vars ("@-vars") in test code.

Repeating Request Helpers

In order for tests to be properly concurrent, it's important that you chain all requests and return the result of this chain at the bottom. This allows the suite to append additional behaviors to the end of the chain. To this end, SuiteHelper provides helpers that allow you to chain a series of requests in one call:

# you can repeat a given number of times...
test "create five identical things" do |device|
  request_times(5) { '/api/widgets', name:'thingy' }.then do
    # In this block, all requests have successfully completed.

# ...or loop over an array of values
test "create five different things" do |device|
  request_each(1..5.to_a) {|n| '/api/widgets', name:"thing #{n}" }.then do
    # In this block, all requests have successfully completed.

Advanced Promise Chaining

Because returned promises chain, it's possible to handle dependent requests further down the promise chain. For example, these two are equivalent:

device.get("/api/widget/#{widget_id}").then do |result|
  device.patch("/api/widget/#{widget_id}", result.merge(name:'new name')).then do |result|
    # Do something with the PATCH response.

device.get("/api/widget/#{widget_id}").then do |result|
  device.patch("/api/widget/#{widget_id}", result.merge(name:'new name'))
end.then do |result|
  # Do something with the PATCH response.

Use this technique to keep chain dependent requests without nesting too deeply in your test code. Remember that every callback must return either a valid result OR a dependent promise!

Deploying to Heroku

When you run a Deathstare test app locally, you can specify multiple concurrent devices.

When you deploy that same Deathstare test app on Heroku, you can specify up to 100 concurrent instances running as well. Each of those instances will present load for the number of concurrent devices you specify on the dashboard.

To set that up, you will have to deploy your test app to Heroku, set up OAuth for the application, and set up three Heroku environment variables:


When you run your test app on Heroku, you will have the option to set a number of concurrent instances (up to 100) for your test run. That comes with the corresponding cost of running those Heroku instances during the test run, but it is relatively inexpensive for the amount of load testing you will be able to generate. Deathstare spins down the instances when the test run completes.


Large-scale load testing for JSON REST APIs







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