Cloudformation metadata API Ruby code

gistfile1.rb

require 'net/http'
require 'base64'
require 'json'

module Cfn
  class << self
    def instance_identity_document()
      Net::HTTP.get(URI('http://169.254.169.254/latest/dynamic/instance-identity/document'))
    end

    def instance_identity_signature()
      Net::HTTP.get(URI('http://169.254.169.254/latest/dynamic/instance-identity/signature'))
    end

    def cfn_authorization_header()
      document = Base64.strict_encode64(instance_identity_document)
      signature = instance_identity_signature.gsub("\n", '')
      "CFN_V1 #{document}:#{signature}"
    end

    def cfn_metadata(stack_name, logical_resource_id, region='us-east-1')
      http = Net::HTTP.start("cloudformation.#{region}.amazonaws.com", 443, use_ssl: true)
      resp = http.get(
        '/?' + URI.encode_www_form(
          {
            'Action' => 'DescribeStackResource',
            'Version' => '2010-05-15',
            'ContentType' => 'JSON',
            'StackName' => stack_name,
            'LogicalResourceId' => logical_resource_id
          }
        ),
        {
          'Authorization' => cfn_authorization_header
        }
      )
      body = JSON.parse(resp.body)
      metadata = body['DescribeStackResourceResponse']['DescribeStackResourceResult']['StackResourceDetail']['Metadata']

      if metadata.nil?
        {}
      else
        JSON.parse(metadata)
      end
    end
  end
end