mailer.json

{
  "mailer": {
    "admin_gui": "http://monitor.domain.com/",
    "mail_from": "sensu@domain.com",
    "mail_to": "tech@domain.com",
    "smtp_domain": "domain.com"
  }
}

mailer.rb

#!/opt/sensu/embedded/bin/ruby
#
# Sensu Extension: mailer
#
# This mailer extension was pretty much copy/pasted from the following authors work
# It got moved to an extension so the sensu doesn't fork bomb itself if you have a lot
# of alerts
#
# Author (sort of) Mike Zupan (http://zcentric.com) @mikezupan
# Taken from Pal-Kristian Hamre (https://github.com/pkhamre | http://twitter.com/pkhamre)
#
# Released under the same terms as Sensu (the MIT license); see LICENSE
# for details.

gem 'mail', '~> 2.5.4'
require 'mail'
require 'timeout'

# patch to fix Exim delivery_method: https://github.com/mikel/mail/pull/546
module ::Mail
  class Exim < Sendmail
    def self.call(path, arguments, destinations, encoded_message)
      popen "#{path} #{arguments}" do |io|
        io.puts encoded_message.to_lf
        io.flush
      end
    end
  end
end

module Sensu::Extension

  class Mailer < Handler

    def post_init
    end

    def definition
      {
        type: 'extension',
        name: 'mailer',
        mutator: 'ruby_hash'
      }
    end

    def name
      definition[:name]
    end

    def description
      'A Mailer handler that will not fork'
    end

    # convert the status to a string
    def status_to_string
      case @event['check']['status']
      when 0
        'OK'
      when 1
        'WARNING'
      when 2
        'CRITICAL'
      else
        'UNKNOWN'
      end
    end

    def short_name
      @event['client']['name'] + '/' + @event['check']['name']
    end

    def action_to_string
     @event['action'].eql?('resolve') ? "RESOLVED" : "ALERT"
    end

    def run(event)
      # Is this event a resolution?
      resolved = event[:action].eql?(:resolve)

      if (resolved || [1, 2, 3].include?(event[:check][:status]))
        check = event[:check]

        admin_gui = @settings["mailer"]["gui"] || 'http://localhost:8080/'
        mail_to = @settings["mailer"]["mail_to"]
        mail_from =  @settings["mailer"]["mail_from"]


        playbook = "Playbook:  #{@event['check']['playbook']}" if @event['check']['playbook']
        body = <<-BODY.gsub(/^\s+/, '')
                #{@event['check']['output']}
                Admin GUI: #{admin_gui}/#/client/Manage/#{@event['client']['name']}
                Host: #{@event['client']['name']}
                Timestamp: #{Time.at(@event['check']['issued'])}
                Address:  #{@event['client']['address']}
                Check Name:  #{@event['check']['name']}
                Command:  #{@event['check']['command']}
                Status:  #{status_to_string}
                Occurrences:  #{@event['occurrences']}
                #{playbook}
              BODY
        subject = "#{action_to_string} - #{short_name}: #{status_to_string}"

        begin
          timeout 10 do
            Mail.deliver do
              to      mail_to
              from    mail_from
              subject subject
              body    body
            end

            yield('mail -- sent alert for ' + short_name + ' to ' + mail_to.to_s, 0)
          end
        rescue Timeout::Error
          yield('mail -- timed out while attempting to ' + @event['action'] + ' an incident -- ' + short_name, 2)
        end
      else
        yield("Mailer not handling", 2)
      end
    end

    def stop
      yield
    end

  end
end