Automatic rotating snapshots of AWS EC2 Linux instances

autosnap.rb

#!/usr/bin/ruby
#
# Take automatic rotating snapshots of your AWS EC2 linux instance(s).
#
# Slap this file into /etc/cron.hourly/ on your EC2 instance,
#   edit the constants at the top of the class to your liking,
#   and give it the execute bit.
#
# Known to work on Ubuntu 14.04 64bit. Presumed to work on most other flavors.
#
# Requirements:
# - ruby
# - gem 'aws-sdk', '~> 2.0' #known to work with 2.0.6.pre 

require 'net/http'
require 'aws-sdk'

class Snapshot
  ACCESS_KEY_ID = someaccesskeyid
  SECRET_ACCESS_KEY = somesecretaccesskey
  AWS_REGION = 'us-west-2' #or whatever you prefer
  ITERATION_MAP = { # Keys must be in order of less frequent to more frequent.
    :monthly => { timestamp_format: '%m/%y', :keep => 2 },
    :weekly => { timestamp_format: '%m/%y-%U', :keep => 4 },
    :daily => { timestamp_format: '%m/%d/%y', :keep => 5 },
    :hourly => { timestamp_format: '%m/%d/%y-%H', :keep => 8 }
  }

  def self.create
    new.save
  end

  def save
    instance.volumes.each do |volume|
      if iteration_for(volume)
        volume.create_snapshot(description: iteration_description_for(volume))
      end
      purge_old_snapshots_for(volume)
    end
  end

  private

  def instance
    @instance ||= Aws::EC2::Instance.new(instance_id, :client => client)
  end

  def instance_id
    @instance_id ||= Net::HTTP.get_response(
      URI.parse('http://169.254.169.254/latest/meta-data/instance-id')
    ).body
  end

  def client
    @client ||= Aws::EC2::Client.new(
      :region => AWS_REGION,
      :access_key_id => ACCESS_KEY_ID,
      :secret_access_key => SECRET_ACCESS_KEY)
  end

  def iteration_description_for(volume)
    description_for(iteration_for(volume))
  end

  def iteration_for(volume)
    @volume_iterations ||= Hash.new do |h, key|
      h[key] = detect_iteration_for(key)
    end
    @volume_iterations[volume]
  end

  def detect_iteration_for(volume)
    ITERATION_MAP.keys.detect do |iteration|
      volume.snapshots.none? {|s| s.description == description_for(iteration) }
    end
  end

  def description_for(iteration)
    "Autosnap #{iteration.capitalize} [#{timestamp_for(iteration)}]"
  end

  def timestamp_for(iteration)
    Time.now.strftime(ITERATION_MAP[iteration][:timestamp_format])
  end

  def purge_old_snapshots_for(volume)
    old_snapshots_for(volume).each do |old_snapshot|
      old_snapshot.delete
    end
  end

  def old_snapshots_for(volume)
    Array.new.tap do |old_snapshots|
      ITERATION_MAP.keys.each do |key|
        old_snapshots << volume.snapshots.
          select {|s| s.description.match(/Autosnap #{key.capitalize}/) }.
          sort {|a,b| b.start_time <=> a.start_time }[ITERATION_MAP[key][:keep],99].
          to_a
      end
    end.flatten
  end

end

Snapshot.create