ztdns.rb

require 'rubydns'
require 'httparty'
require 'lru_redux'

class ZeroTierAPI
  include HTTParty

  base_uri "https://my.zerotier.com/api"
  headers 'Authorization' => "Bearer #{ENV['ZT_API_TOKEN']}"

  def initialize
    @cache = LruRedux::TTL::ThreadSafeCache.new(100, 300)
  end

  def members
    @cache.getset('members') do
      network_members = self.class.get("/network/#{ENV['ZT_NETWORK_ADDRESS']}/member").keys
      network_members.map do |member|
        self.class.get("/network/#{ENV['ZT_NETWORK_ADDRESS']}/member/#{member}")
      end
    end
  end

  def member(name)
    members.detect { |m| m['nodeId'] == host || m['name'] == host }      
  end
end


INTERFACES = [
    [:udp, "0.0.0.0", 5300],
    [:tcp, "0.0.0.0", 5300]
]

ZT = ZeroTierAPI.new

RubyDNS::run_server(:listen => INTERFACES) do

  match(/\w+\.#{ENV['ZT_NETWORK_NAME']/) do |transaction|    
    host, _ = transaction.name.split('.', 2)
    
    member = ZT.member(host)

    # inactive members sometimes have subnets as their ipAssignment
    if member && member['config']['ipAssignments'].first !~ /\//
      transaction.respond!(member['config']['ipAssignments'].first, ttl: 300)
    else
      transaction.fail!(:NXDomain)
    end
  end

  otherwise do |transaction|
    transaction.fail!(:NXDomain)
  end
end