Ab Crunch

by TrueCar

The idea behind Ab Crunch is that basic performance metrics and standards should be effortless, first-class citizens in the development process, with frequent visibility and immediate feedback when performance issues are introduced.

Other tools exist for measuring performance, but we found that they had some drawbacks:

• Not easily integrated into routine development practices, such as automated testing and CI
• Take a long time to set up.
• Take a long time to use.

We wanted a tool that, while simple, was valid enough to surface basic performance issues and fast/easy enough to use throughout all our projects.

Ab Crunch uses Apache Bench to run various strategies for load testing web sites. It generates rake tasks for running all or some of our tests. These can be configured to be just informational, or to fail when specified standards are not met. The rake tasks can then be added to our Continuous Integration (CI) builds, so builds fail when performance degrades.

Credits

Christopher "Kai" Lichti, Author
Aaron Hopkins, adviser / contributed strategies
John Williams, adviser / contributed strategies
TrueCar, Inc, for giving us jobs and letting us share this gem

Prerequisites

Must have Apache Bench installed and 'ab' on your path

Quick Start Guide

To see some immediate action, require the gem, and run 'rake abcrunch:example'

Now to use it on your own pages:

First, define the pages you want to test, and (optionally), the performance requirements you want them to meet. If you exclude any requirements, your load test will be informational only, and won't log or raise any errors based on performance standards.

For Example:

@load_test_page_sets = {
  :production => [
    {
      :name => "Google home page",
      :url => "http://www.google.com/",
      :min_queries_per_second => 20,
      :max_avg_response_time => 1000,
    },
    {
      :name => "Facebook home page",
      :url => "http://www.facebook.com/",
    }
  ],
  :staging => [
    {
      :name => "Github home page",
      :url => "http://www.github.com/",
      :max_avg_response_time => 1000,
    }
  ]
}

require 'abcrunch'
AbCrunch::Config.page_sets = @load_test_page_sets

In Rails, you can do this in your development and test environments.

Once you've configured Ab Crunch, you can run rake tasks to load test your pages, like this:

rake abcrunch:staging
 - or -
rake abcrunch:all

Configuring Pages

• :name: (required) User-friendly name for the page.

• :url: (required) Url to test. Can be a string or a Proc. Proc example:

    :url => proc do
      "http://www.google.com/?q=#{['food','coma','weirds','code'][rand(4)]}"
    end,
  

Performance requirements (will raise so CI builds break when requirements fail)

• :min_queries_per_second: page must support at least this many QPS
• :max_avg_response_time: latency for the page cannot go higher than this

Other Options

• :num_requests - how many requests to make during each (of many) runs [Default: 50]
• :max_latency - global maximum latency (in ms) considered to be acceptable [Default: 1000]
• :max_degradation_percent - global max percent latency can degrade before being considered unacceptable [Default: 0.5 (iow 50%)]

Examples

Iterative Optimization

Running a focus load test to iterate fixing a performance issue.

If a specific page is too slow, you can iterate on that page using a focus rake task, like so:

rake abcrunch:dev:focus[3]

Configuring the same URLS in multiple environments (dev, qa, staging, prod...)

Here's an example showing how you might dry up the AbCrunch configuration to support multiple environments.

def init_env
  if ['development', 'test'].include? RAILS_ENV
    require 'abcrunch'
    AbCrunch::Config.page_sets = ab_crunch_page_sets
  end
end

def ab_crunch_page_sets
  def page_with_domain(page, domain)
    new = page.clone
    new[:url] = page[:url].gsub '<domain>', domain
    new
  end
  
  result = {
    :dev => AB_CRUNCH_PAGE_SET_TEMPLATE.collect { |page| page_with_domain(page, 'http://localhost:3000') },
    :qa => AB_CRUNCH_PAGE_SET_TEMPLATE.collect { |page| page_with_domain(page, 'http://qa.myapp.com') },
    :staging => AB_CRUNCH_PAGE_SET_TEMPLATE.collect { |page| page_with_domain(page, 'http://staging.myapp.com') },
    :prod => AB_CRUNCH_PAGE_SET_TEMPLATE.collect { |page| page_with_domain(page, 'http://www.myapp.com') },
  }
  
  result
end

AB_CRUNCH_PAGE_SET_TEMPLATE = [
  {
    :name => "Home",
    :url => "<domain>/",
    :min_queries_per_second => 50,
  },
  {
    :name => "Blog",
    :url => "<domain>/blog?user=honest_auto",
    :max_avg_response_time => 450,
  }
]

Known Gotcha

Apache Bench does not like urls that just end with the domain. For example:
http://www.google.com is BAD, but
http://www.google.com/ is fine, for reasons surpassing understanding.
...so for root level urls, be sure to add a trailing slash.

License

The MIT License Copyright (c) 2011 TrueCar, Inc.

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.