Demo script for AWSAdvent 2014 blog post

awsha.rb

#!/usr/bin/ruby

require 'fog'
require 'json'
require 'open-uri'

module AWSAdvent
  class Demo
    attr_reader :instance, :compute, :server

    VIP = '172.31.36.57'.freeze
    VOLUME = 'vol-deadbeef'.freeze

    def initialize
      @compute = Fog::Compute.new(:provider => 'AWS',
                                  :use_iam_profile => true)
      @instance = load_instance
      @server = @compute.servers.get(@instance['instanceId'])
    end

    def action_master
      # Take the elastic network interface IP address
      puts "Binding ENI secondary to me"
      @compute.assign_private_ip_addresses(@server.network_interfaces.first['networkInterfaceId'],
                                           'PrivateIpAddresses' => [VIP],
                                           'AllowReassignment' => true)

      puts "Associating EBS device"
      # Associate device
      # Amazon's API names all devices /dev/sdXX, whereas newer Linuxes present them as device nodes /dev/xvdXX
      @compute.attach_volume(@instance['instanceId'], VOLUME, '/dev/sdf')
      # Wait for a while for it to get attached
      sleep 30
      # Mount disk if something's not already mounted
      unless `mount`.split("\n").select { |l| l.include?('/mnt') }.length > 0
        system('mount /dev/xvdf /mnt')
      end
      # Start httpd
      system('service httpd start')
    end

    def action_backup
       # Relinquish the elastic IP address -- nothing to do
       # Stop httpd
       system('service httpd stop')
       # Dismount disk
       system('umount /mnt')
       # Disassociate device
       @compute.detach_volume(VOLUME)
    end

    private
        
    def load_instance
      JSON.parse(open('http://169.254.169.254/latest/dynamic/instance-identity/document').read)
    end
  end
end

awsadvent = AWSAdvent::Demo.new
action = "action_#{ARGV[0]}".to_sym
if awsadvent.respond_to?(action)
  awsadvent.send(action)
else
  puts "Unknown action: #{ARGV[0]}"
  exit 1
end