serve.rb

require 'rubydns'

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

IN = Resolv::DNS::Resource::IN

UPSTREAM = RubyDNS::Resolver.new([[:udp, "8.8.8.8", 53], [:tcp, "8.8.8.8", 53]])

# name => [
#   [ "label", TYPE, [args to create type]... ]
# ]
# args can include options which are stripped. 
# the only supported option is alias, which acts like an AWS ALIAS type

CONFIG = {
  :subspace => [
    ["@",   IN::SOA,
      ["subspace.bugsplat.info", "domains.bugsplat.info", Time.now.to_i, 0, 0, 0, 30]
    ],
    ["@",   IN::NS,
      ["dns1.bugsplat.info"],
      ["dns2.bugsplat.info"]
    ],
    ["@",   IN::A,
      ['subspace.bugsplat.info', alias: true],
    ],
    ["www", IN::A,
      ['subspace.bugsplat.info', alias: true],
    ],
  ],
  "whatever.com"  => :subspace,
  "whatever2.net"  => :subspace,
}

def alias_for(name, resource_class)
  begin
    UPSTREAM.addresses_for(name, resource_class)
  rescue RubyDNS::ResolutionFailure
    nil
  end
end

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

  CONFIG.each do |domain, config|
    next if domain.is_a? Symbol

    config = CONFIG[config] if config.is_a? Symbol

    config.each do |nameconfig|
      nameconfig = nameconfig.dup
      name = nameconfig.shift
      type = nameconfig.shift

      values = nameconfig

      fqdn = name == '@' ? domain : "#{name}.#{domain}"

      match(fqdn, type) do |transaction|
        rrs = []

        if values.length == 1 && values.last.last.kind_of?(Hash) && values.last.last[:alias]
          rrs = alias_for(values.last.first, type).map { |v| type.new(v) }
        else
          values.each do |value|
            value = value.dup
  
            options = value.pop if value.last.kind_of?(Hash)
  
            value = value.map { |v| v.kind_of?(String) && v =~ /[a-zA-Z]/ ? Resolv::DNS::Name.create(v) : v }
  
            rrs << type.new(*Array(value))
          end
        end

        transaction.send(:append_question!)
        transaction.add(rrs, ttl: 30)
      end
    end
  end

    # Default DNS handler
  otherwise do |transaction|
    transaction.fail!(:NXDomain)
  end
end