A simple Ruby script for creating or updating a Linode DNS A record for the current host (i.e. - Dynamic DNS)

linode_ddns.rb

#!/usr/bin/env ruby

require 'linode'
require 'open-uri'

$api_key = "MY LINODE API KEY"
$subdomain = "my.subdomain.example.com"

# Updates a Linode DNS record. Can be used to create a dynamic DNS within a
# domain of your own. Just set the subdomain to whatever.
# Requires Ruby, linode (`gem install linode`), and an account with Linode
# (linode.com).
class DNSUp
  attr_accessor :linode, :subdomain, :domain, :name, :target, :type

  def initialize(options = {})
    options = {
      :api_key => $api_key,
      :subdomain => $subdomain,
      :type => 'A'
    }.merge(options)

    @linode = Linode.new(:api_key => options[:api_key])
    @subdomain = options[:subdomain]
    @name = @subdomain.split('.').first
    @domain = @subdomain.sub(/\A#{@name}\./, '')
    @type = options[:type] || 'A'
    @target = options[:target] || self.class.remote_ip
  end

  def self.remote_ip
    @remote_ip ||= open('http://icanhazip.com').read.chomp
  end

  def domain_id
    @domain_id ||= @linode.domain.list.find do |d|
      d.domain == @domain
    end.domainid
  end

  def resource_list
    raise(InvalidDomain, @domain) if domain_id.nil?
    @resource_list ||= @linode.domain.resource.list(:DomainID => domain_id)
  end

  def resource
    @resource ||= resource_list.find { |r| r.name == @name }
  end

  def resource_options
    {
      :DomainID => domain_id,
      :Target => target,
      :Name => name
    }
  end

  def update
    if resource.nil?
      create
    else
      options = resource_options.merge(:ResourceID => resource.resourceid)
      puts "Updating... #{options.inspect}"
      @linode.domain.resource.update(options)
    end
  end

  def create
    options = resource_options.merge(:Type => type)
    puts "Creating... #{options.inspect}"
    @linode.domain.resource.create(options)
  end

  class InvalidDomain < Exception; end
end

if __FILE__ == $0
  DNSUp.new.update
end