Fetch latest Canonical Ubuntu AMI ID for a given region

latest_ubuntu_ami.rb

require 'aws-sdk-resources'
require 'diskcached'

# ...
 
  CANONICAL_AWS_ID      = '099720109477'  # AWS ID for Ubuntu's publisher
  DATE_MATCHER          = /(\d\d\d\d)(\d\d)(\d\d)(\.\d+)?\Z/

  # Returns the latest Canonical Ubuntu AMI for a given
  # Ubuntu version, AWS region, architecture, and root device type.
  def latest_ubuntu_ami(ubuntu_version, region = 'us-east-1',
    arch = 'x86_64', root_type = 'ebs', vm_type = "hvm")
    ec2 = Aws::EC2::Resource.new(region: region)
    cache_key = [ubuntu_version, region, arch, root_type, vm_type].join('-')
    diskcache = Diskcached.new(File.join(PROJECT_DIR, 'tmp', 'AMIcache'))
    diskcache.cache(cache_key) do
      candidates = ec2.images(owners: [CANONICAL_AWS_ID]).select do |image|
        # (image.type                 == :machine)      &&
        (image.root_device_type     == root_type)     &&
        (image.architecture         == arch)          &&
        (image.virtualization_type  == vm_type)       &&
        ((image.name || '')         =~ DATE_MATCHER)  &&
        ((image.name || '')         =~ /#{ubuntu_version}/)
      end
      candidates.sort{|a,b| a.name <=> b.name}.last.id
    end
  end