Advanced Serverspec

Testing the outcome of infrastructure provisioning is an operator’s bread and butter. Good cookbook tests create predictable automation, and can be added to once problems are inevitably discovered. Serverspec is a huge part of ensuring that infrastructure being provisioned via chef is actually in the desired state.

Combining ruby’s builtin libraries to parse and manipulate configuration files with serverspec is a quick and simple win. We’re no longer bound by having to use overly complex, brittle regexes to ensure files are created correctly.

Here’s a few ways to pull in rubygems when writing serverspec;

  • Simply use ruby include
  • Add a Gemfile to your serverspec folder
  • Use Gem::DependencyInstaller in the spec_helper.rb

Here’s an example of installing the inifile gem in your spec_helper.rb.

Install a gem in spec_helper.rb
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begin
  Gem::Specification.find_by_name('inifile')
rescue Gem::LoadError
  require 'rubygems/dependency_installer'
  Gem::DependencyInstaller.new(Gem::DependencyInstaller::DEFAULT_OPTIONS).install('inifile')
end

Here’s a few examples of using the ini gem we installed to make our tests better.

Parse an ini file
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require 'inifile'

describe 'conf file tests'
  program_conf = '/my/path/to/important/program.conf'

  it 'writes out a program.conf file' do
    expect(file program_conf).to be_file
  end

  # Regex test
  it 'has the correct maxmemory value' do
    expect(file(program_conf).content).to match/^program\.java\.maxmemory.*=.*512.*$/
  end

  # Lib test
  program_ini = IniFile.load(program_conf)
  it 'has the correct maxmemory value' do
    expect(program_ini['global']['program.java.maxmemory']).to eq(512)
  end
end

Parsing config files with similar libs that would be consuming them in production provides a lightweight, implied method of testing that those files are valid. It’s also a straightforward, programmatic approach to getting values out of configuration files. And not just scalar values, but lists and arrays.

Here’s a more in-depth example, using rspec.

Parse a json file, check some values, and ensure all items are present in a list
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describe 'json config' do
  config_file = '/etc/default.json'
  conf = JSON.parse(File.read(config_file))

  it 'does *not* have the unkey key' do
    expect(conf).to_not have_key('unkey')
  end

  it 'sets foo to bar' do
    expect(conf['foo']).to eq('bar')
  end

  expected_items = [
    '127.0.0.128',
    '127.0.0.126',
    '127.0.0.127'
  ]

  describe conf['items'] do
    it { should match_array(expected_items) }
  end
end
Apr 23rd, 2015

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