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Monitor your service's availability through a simple, clean DSL

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README.markdown

Outpost

Build status: Build Status

Features

Outpost is a tool to monitor the state of your service (not server). What does it mean?

It means:

  • it can monitor the state of a server, such as MySQL;
  • it can monitor some business rule to see if everything is running accordingly (such as cron jobs)
  • it can monitor several servers
  • it can monitor whatever you can code with Ruby

It will connect to the related machines (it won't have any proxies/agents running on the servers to report data) and collect the data. The idea is to be completely uncoupled with the systems. It should report a status per declared system.

The idea is to make a reliable framework for the Ruby developer to create his own monitoring rules. So, summing it all up, Nagios in Ruby, much cooler!

Information and examples

Installing

Outpost is tested with Ruby 1.8.7 and Ruby 1.9.3.

gem install outpost

Starting

To create your Outposts, you must require 'outpost'. You also need to include 'outpost/scouts' if you want to use the supplied scouts. Example:

require 'outpost'
require 'outpost/scouts'

class Monitor < Outpost::Application
  using Outpost::Scouts::Http => "web page" do
    options :host => 'localhost', :port => 3000
    report :up, :response_code => 200
  end
end

monitor = Monitor.new
monitor.run
p monitor.messages # => ["Outpost::Scouts::Http: 'web page' is reporting up."]

How it works

Consider the following example:

require 'outpost'
require 'outpost/scouts'

class HttpOutpostExample < Outpost::Application
  using Outpost::Scouts::Http => "web page" do
    options :host => 'localhost', :port => 3000
    report :up, :response_code => 200
    report :down, :response_body => {:match => /Ops/}
  end
end
outpost = HttpOutpostExample.new
outpost.run # => :down

In this simple example, an Outpost was created to monitor a web server running on localhost at port 3000. Every time #run is called, the outpost will run associated rules (in this example, check if the HTTP response code is 200 and report "up" if it does and also check if the response body matches /Ops/, reporting "down" in that case).

Outpost

Outpost is the description of the system and provides a DSL to do it. Check "How it works" section for an example, or check the integration tests for more.

Scout

Scout are pure Ruby classes that will test your server. For instance, check the Outpost::Scouts::Http example below:

module Outpost
  module Scouts
    class Http < Outpost::Scout
      extend Outpost::Expectations::ResponseCode
      extend Outpost::Expectations::ResponseBody

      attr_reader :response_code, :response_body

      def setup(options)
        @host = options[:host]
        @port = options[:port] || 80
        @path = options[:path] || '/'
      end

      def execute
        response = Net::HTTP.get_response(@host, @path, @port)
        @response_code = response.code.to_i
        @response_body = response.body
      end
    end
  end
end

It must implement the #setup and #execute methods. The magic lies in the #execute method, where you can implement any kind of logic to test whether your system is up or not. You may also include expectations in order to process the output of your system. For more information about expectations, check the section below.

If you're interested in the data the Scouts got through a measurement, you can tell Outpost that it must save that data after the measurement is run. That way you can inquiry it for further analysis. This way, you can have Scouts without any expectations/reports, so you can collect data without telling if the system is either up or down. You can check an usage example in the Reports integration test.

Expectations

Consider the following code snippet, taken from previous examples:

report :up, :response_code => 200
report :down, :response_body => {:match => /Ops/}

In the example above, :response_code and :response_body are expectations, responsible to get Scout's output and evaluate it, in order to determine a status.

They must be registered into each Scout that wish to support different types of expectations. You can supply a block or an object that respond to #call and return true if any of the rules match. It will receive an instance of the scout (so you can query current system state) as the first parameter and the state defined in the #report method as the second.

So you can easily create your own expectation. Let's recreate the :response_code in Outpost::Scouts::Http:

module Outpost
  module Scouts
    class Http < Outpost::Scout
      expect(:response_code) { |scout,code| scout.response_code == code }

      attr_reader :response_code

      def setup(options)
        @host = options[:host]
        @port = options[:port] || 80
        @path = options[:path] || '/'
      end

      def execute
        response = Net::HTTP.get_response(@host, @path, @port)
        @response_code = response.code.to_i
      end
    end
  end
end

You can also check the supplied expectations in the source of the project to have an idea on how to implement more complex rules.

Notifiers

Notifiers query Outposts and act upon its status and reports. In the example below, an Email notifier is being used to report failures in the system to the system administrator:

require 'outpost'
require 'outpost/scouts'
require 'outpost/notifiers'

class HttpOutpostExample < Outpost::Application
  notify Outpost::Notifiers::Email, {
    :from => 'outpost@example.com',
    :to   => 'sleep_deprived_admin@example.com'
  }

  using Outpost::Scouts::Http => "web page" do
    options :host => 'localhost', :port => 3000
    report :up, :response_code => 200
    report :down, :response_body => {:match => /Ops/}
  end
end
outpost = HttpOutpostExample.new
outpost.run # => :down

# Will send an email to the poor sleep-deprived Sys Admin if the system is
# down.
outpost.notify if outpost.down?

Creating Outpost applications programatically

It is also possible to create Outposts without having to subclass it. Use the methods #add_scout and #add_notifier and you're set:

outpost = Outpost::Application.new

outpost.add_scout Outpost::Scouts::Http => 'master http server' do
  options :host => 'localhost', :port => 9595
  report :up, :response_code => 200
end

outpost.run

This is good when you want to have some sort of template (by inheriting from Outpost::Application) and then configure things as you go.

TODO

See TODO.

License

MIT License.

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