Simple script to audit AWS EC2 Reserved Instances vs Instances running.

riaudit.rb

#!/usr/bin/env ruby

# Audits your reserved instances vs your running instances, and reports back. 
# If you want to run this from an AWS instance, its IAM Role must be granted at least the following:
#
#{
# "Statement": [
# {
# "Action": [
# "ec2:DescribeInstances",
# "ec2:DescribeReservedInstances",
# ],
# "Effect": "Allow",
# "Resource": "*"
# }
# ]
# }

require 'rubygems'
require 'trollop' # Option parsing made stupid easy
require 'aws-sdk'

class Hash
  
  # Compares another Hash to this one, and returns a Hash of the differences
  def deep_diff(b)
    a = self
    (a.keys | b.keys).inject({}) do |diff, k|
      if a[k] != b[k]
        if a[k].respond_to?(:deep_diff) && b[k].respond_to?(:deep_diff)
          diff[k] = a[k].deep_diff(b[k])
        else
          diff[k] = [a[k], b[k]]
        end
      end
      diff
    end
  end
end

class AZ
  attr_accessor :name, :instances, :ris

  def initialize(name)
    @name = name
    @instances = Hash.new
    @ris = Hash.new
  end

  # Add a running instance (I)
  def add_instance(entry)
    @instances[entry] = @instances.has_key?(entry) ? @instances[entry] + 1 : 1
  end
  
  # Add a reserved instance (RI), and an optional number of them
  def add_ris(entry, ricount = 1)
    @ris[entry] = @ris.has_key?(entry) ? @ris[entry] + ricount : ricount
  end
  
  # Analyze the current AZ object, outputting relevant differences
  def analyze(prefix = '', verbose = false)
    @ris.deep_diff(@instances).each_pair {|key, value|
     (ri,i) = value
     ri = 0 if ri.nil?
     d = i - ri
     if verbose
      puts "#{prefix}#{key} Reserved Instances: #{ri} Instances Running: #{i} Difference: #{d}"
     else
      puts "#{prefix}#{key} RI: #{ri} I: #{i} D: #{d}"
     end
    }
  end
end

# Option parsing via Trollop
opts = Trollop::options do
  opt :region, "AWS Region",
    :type => String,
    :default => 'us-east-1'
  opt :verbose, "Spell out the variables"
  opt :debug, "Be noisy"
end

# If you need to deal with keys/credentials, do that here.
ec2 = AWS::EC2.new(:region => opts[:region])
AZs = Hash.new

# Collect active RIs, add them to the appropriate AZ object
ec2.reserved_instances.each {|ri|
  next unless ri.state == 'active'
  puts "[d] RI id: #{ri.id} #{ri.availability_zone} #{ri.instance_type} #{ri.instance_count}" if opts[:debug]
    
  unless AZs.has_key?(ri.availability_zone)
    AZs[ri.availability_zone] = AZ.new(ri.availability_zone)
  end
  
  AZs[ri.availability_zone].add_ris(ri.instance_type, ri.instance_count)
    
}

# Collect running instances, add them to the appropriate AZ object
ec2.instances.each {|i|
  next unless i.status.to_s == 'running'
  puts "[d] I id: #{i.id} #{i.availability_zone} #{i.instance_type}" if opts[:debug]
    
  unless AZs.has_key?(i.availability_zone)
    AZs[i.availability_zone] = AZ.new(i.availability_zone)
  end
    
  AZs[i.availability_zone].add_instance(i.instance_type)
    
}

# Analyze each AZ
AZs.each_pair {|name, az|
  puts "\nAZ: #{name}"
  
  az.analyze("\t", opts[:verbose]) # we prefix a tab, for show
}