update_userdata.rb

# gem install aws-sdk-v1

require 'aws-sdk-v1'
require 'tempfile'
require 'time'
require 'json'

AWS.config(:ec2_region => 'eu-west-1', :auto_scaling_region => 'eu-west-1')

as_group_name = ENV['AS_GROUP']
as_client     = AWS::AutoScaling.new

if !as_group_name or as_group_name.empty?
  abort 'Specify an autoscaling group in AS_GROUP'
end

group     = as_client.groups[as_group_name]
old_conf  = group.launch_configuration

tempfile = Tempfile.new(['userdata', '.json'])

tempfile.write(JSON.pretty_generate(
  JSON.load(old_conf.user_data),
  :indent => '    '
))

tempfile.rewind

system("#{ENV['EDITOR']} #{tempfile.path}")

user_data = tempfile.read

puts 'Creating launch configuration...'

ami_id  = ENV['AMI_ID'] || old_conf.image_id
iam_id  = ENV['IAM_ID'] || old_conf.iam_instance_profile
options = {
  :detailed_instance_monitoring => old_conf.detailed_instance_monitoring,
  :key_pair                     => old_conf.key_pair,
  :security_groups              => old_conf.security_groups.to_a,
  :user_data                    => user_data,
  :iam_instance_profile         => iam_id,
  :block_device_mappings        => old_conf.block_device_mappings.to_a
}

if old_conf.spot_price
  options[:spot_price] = old_conf.spot_price
elsif ENV['SPOT_PRICE']
  options[:spot_price] = ENV['SPOT_PRICE']
end

new_conf = as_client.launch_configurations.create(
  Time.now.strftime("#{as_group_name}-%Y%m%d-%H%M%S"),
  ami_id,
  ENV['INSTANCE_TYPE'] || old_conf.instance_type,
  options
)

puts 'Updating autoscaling group...'

group.update(:launch_configuration => new_conf)