Sensu Plugin

This is a framework for writing your own Sensu plugins and handlers. It's not required to write a plugin (most Nagios plugins will work without modification); it just makes it easier.

Examples of plugins written with and without it can be found in the sensu-plugins organization.

Checks and Metrics

To implement your own check, subclass Sensu::Plugin::Check::CLI, like this:

require 'sensu-plugin/check/cli'

class MyCheck < Sensu::Plugin::Check::CLI

  check_name 'my_awesome_check' # defaults to class name
  option :foo, :short => '-f' # Mixlib::CLI is included

  def run
    ok "All is well"
  end

end

This will output the string "my_awesome_check OK: All is well" (like a Nagios plugin), and exit with a code of 0. The available exit methods, which will immediately end the process, are:

• ok
• warning
• critical
• unknown

You can also call message first to set the message, then call an exit method without any arguments (for example, if you want to choose between WARNING and CRITICAL based on a threshold, but use the same message in both cases).

For a metric, you can subclass one of the following:

• Sensu::Plugin::Metric::CLI::JSON
• Sensu::Plugin::Metric::CLI::Graphite
• Sensu::Plugin::Metric::CLI::Statsd
• Sensu::Plugin::Metric::CLI::Dogstatsd
• Sensu::Plugin::Metric::CLI::Influxdb
• Sensu::Plugin::Metric::CLI::Generic

Instead of outputting a Nagios-style line of text, these classes will output differently formated messages depending on the class you chose.

require 'sensu-plugin/metric/cli'

class MyJSONMetric < Sensu::Plugin::Metric::CLI::JSON

  def run
    ok 'foo' => 1, 'bar' => 'anything'
  end

end

require 'sensu-plugin/metric/cli'

class MyGraphiteMetric < Sensu::Plugin::Metric::CLI::Graphite

  def run
    ok 'sensu.baz', 42
  end

end

require 'sensu-plugin/metric/cli'

class MyStatsdMetric < Sensu::Plugin::Metric::CLI::Statsd

  def run
    ok 'sensu.baz', 42, 'g'
  end

end

require 'sensu-plugin/metric/cli'

class MyDogstatsdMetric < Sensu::Plugin::Metric::CLI::Dogstatsd

  def run
    ok 'sensu.baz', 42, 'g', 'env:prod,myservice,location:us-midwest'
  end

end

require 'sensu-plugin/metric/cli'

class MyInfluxdbMetric < Sensu::Plugin::Metric::CLI::Influxdb

  def run
    ok 'sensu', 'baz=42', 'env=prod,location=us-midwest'
  end

end

require 'sensu-plugin/metric/cli'

class MyInfluxdbMetric < Sensu::Plugin::Metric::CLI::Generic

  def run
    ok metric_name: 'metric.name', value: 0
  end

end

JSON output takes one argument (the object), and adds a 'timestamp' key if missing. Graphite output takes two arguments, the metric path and the value, and optionally the timestamp as a third argument. Time.now.to_i is used for the timestamp if it is not specified. Statsd output takes three arguments, the metric path, the value and the type. Dogstatsd output takes three arguments, the metric path, the value, the type and optionally a comma separated list of tags, use colons for key/value tags, i.e. env:prod. Influxdb output takes two arguments, the measurement name and the value or a comma separated list of values, use = for field/value, i.e. value=42, optionally you can also pass a comma separated list of tags and a timestamp Time.now.to_i is used for the timestamp if it is not specified. Generic output takes a dictionary and can provide requested output format with same logic. And inherited class will have a --metric_format option to switch between different output formats.

Exit codes do not affect metric output, but they can still be used by your handlers.

Some metrics may want to output multiple values in a run. To do this, use the output method, with the same arguments as the exit methods, as many times as you want, then call an exit method without any arguments.

For either checks or metrics, you can override output if you want something other than these formats.

Options

For help on setting up options, see the mixlib-cli documentation. Command line arguments that are not parsed as options are available via the argv method.

Utilities

Various utility methods will be collected under Sensu::Plugin::Util. These won't depend on any extra gems or include actual CLI checks; it's just for common things that many checks might want to do.

Handlers

For your own handler, subclass Sensu::Handler. It looks much like checks and metrics; see the handlers directory for examples. Your class should implement handle. The instance variable @event will be set for you if a JSON event can be read from stdin; otherwise, the handler will abort. Output to stdout will go to the log.

You can decide if you want to handle the event by overriding the filter method; but this also isn't documented yet (see the source; the built in method does some important filtering, so you probably want to call it with super).

Important!

Filtering of events is now deprecated in Sensu::Handler and disabled by default as of version 2.0.

Event filtering in this library may be enabled on a per-check basis by setting the value of the check's enable_deprecated_filtering attribute to true.

These built-in filters will be removed in a future release. See this blog post for more detail.

Mutator

For your own mutator, subclass Sensu::Mutator. It looks much like checks and metrics; Your class should implement mutate. The instance variable @event will be set for you if a JSON event can be read from stdin; otherwise, the mutator will abort. Output to stdout will then be piped through to the handler. As described in the docs if a mutator fails to run the event will not be handled.

The example mutator found here will look like so:

require 'sensu-mutator'

class MyMutator < Sensu::Mutator

  def mutate
    @event.merge!(:mutated => true)
  end

end

Plugin settings

Whether you are writing a check, handler or mutator, Sensu's configuration settings are available with the settings method (loaded automatically when the plugin runs). We recommend you put your custom plugin settings in a JSON file in /etc/sensu/conf.d, with a unique top-level key, e.g. my_custom_plugin:

{
  "my_custom_plugin": {
    "foo": true,
    "bar": false
  }
}

And access them in your plugin like so:

def foo_enabled?
  settings['my_custom_plugin']['foo']
end

Sensu Go enablement

This plugin provides basic Sensu Go enablement support to make it possible to continue to use existing Sensu plugin handlers and mutators for Sensu Core 1.x event model in a backwards compatible fashion.

Sensu Go event mapping

The provided mutator command mutator-sensu-go-into-ruby.rb will mutate the Sensu Go event into a form compatible for handlers written to consume Sensu Core 1.x events. Users may find this mutator useful until such time that community plugin handler are updated to support Sensu Go event model directly.

Sensu plugins which provide either mutators or handlers can benefit from provided Sensu Go enablement support in the form of mixin commandline option support. Once plugins update to the latest sensu-plugin version, all mutator and handler commands will automatically grow an additional commandline argument --map_go_event_into_ruby

Custom attributes

For backwards compatibility, you can store custom entity and check attributes as a json string in a specially named annotation. By default the annotation key is sensu.io.json_attributes, but can be overridden using the environment variable MAP_ANNOTATION. The json string stored in the MAP_ANNOTATION key will be converted into a ruby hash and merged into the ruby event hash object as part of the event mapping.

Contributing

• Fork repository
• Add functionality and any applicable tests
• Ensure all tests pass by executing bundle exec rake test
• Open a pull request

You may run individual tests by executing bundle exec rake test TEST=test/external_handler_test.rb

License

Copyright 2011 Decklin Foster

Released under the same terms as Sensu (the MIT license); see LICENSE for details.