Add metric for count of instances in AWS AutoScaling group
user
```ruby
#!/usr/bin/env ruby
#
# AutoScaling Group Instance Metrics
# ===
#
# Get a count of instances in a given AutoScaling group
#
# Copyright 2013 Bashton Ltd http://www.bashton.com/
#
# Released under the same terms as Sensu (the MIT license); see LICENSE
# for details.
#
# Needs fog gem

require 'rubygems' if RUBY_VERSION < '1.9.0'
require 'sensu-plugin/metric/cli'
require 'fog'

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

  option :groupname,
    :description => "Name of the AutoScaling group",
    :short => "-g GROUP_NAME",
    :long => "--autoscaling-group GROUP_NAME"

  option :scheme,
    :description => "Metric naming scheme, text to prepend to metric",
    :short => "-s SCHEME",
    :long => "--scheme SCHEME",
    :default => ""

  option :aws_access_key,
    :short => '-a AWS_ACCESS_KEY',
    :long => '--aws-access-key AWS_ACCESS_KEY',
    :description => "AWS Access Key. Either set ENV['AWS_ACCESS_KEY_ID'] or provide it as an option",
    :required => true

  option :aws_secret_access_key,
    :short => '-k AWS_SECRET_ACCESS_KEY',
    :long => '--aws-secret-access-key AWS_SECRET_ACCESS_KEY',
    :description => "AWS Secret Access Key. Either set ENV['AWS_SECRET_ACCESS_KEY'] or provide it as an option",
    :required => true

  option :aws_region,
    :short => '-r AWS_REGION',
    :long => '--aws-region REGION',
    :description => "AWS Region (such as eu-west-1).",
    :default => 'us-east-1'

  def run
    if config[:scheme] == ""
      graphitepath = "#{config[:groupname]}.autoscaling.instance_count"
    else
      graphitepath = config[:scheme]
    end
    begin
      as = Fog::AWS::AutoScaling.new(
        :aws_access_key_id      => config[:aws_access_key],
        :aws_secret_access_key  => config[:aws_secret_access_key],
        :region             => config[:aws_region])

      count = as.groups.get(config[:groupname]).instances.map{|i| i.life_cycle_state}.count('InService')
      output graphitepath, count

    rescue Exception => e
      puts "Error: exception: #{e}"
      critical
    end
    ok
  end

end
```
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