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 either Sensu::Plugin::Metric::CLI::JSON or Sensu::Plugin::Metric::CLI::Graphite. Instead of outputting a Nagios-style line of text, these classes will output JSON-serialized objects or Graphite messages.

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

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.

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

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

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

jkugler / sensu-plugin