aws_autoscaling_cron.rb

#!/usr/bin/env ruby
require 'syslog'
require 'net/http'
require 'aws-sdk'

Syslog.open

AWS.config({
:access_key_id => '<iam user key>',
:secret_access_key => '<iam user secret>'
})

metadata_endpoint = 'http://169.254.169.254/latest/meta-data/'
instance_id = Net::HTTP.get( URI.parse( metadata_endpoint + 'instance-id' ) )

auto_scaling = AWS::AutoScaling.new
auto_scaling.groups.each { |group|
  instance = group.ec2_instances.filter('instance-state-name', 'running').first
	if( instance.instance_id == instance_id )
		command = ARGV * ' '
		Syslog.alert( 'running cron on ' + instance_id + ': ' + command )
		`#{command}`
	end
}

aws_autoscaling_cron.sh

#!/bin/bash
source "/usr/local/rvm/scripts/rvm"
cd "$(dirname "$0")"
./aws_autoscaling_cron.rb "$@"

aws_iam_policy.json

{
  "Statement": [
    {
      "Action": [
        "autoscaling:DescribeAutoScalingGroups",
        "autoscaling:DescribeAutoScalingInstances",
        "ec2:DescribeInstanceAttribute",
        "ec2:DescribeInstanceStatus",
        "ec2:DescribeInstances"
      ],
      "Effect": "Allow",
      "Resource": [
        "*"
      ]
    }
  ]
}

crontab

#run a command every day at midnight
0 0     * * *   ubuntu  /aws_autoscaling_cron.sh <command> <parameters> > /dev/null 2> /dev/null