dns_record.rb

class DnsRecord < ActiveRecord::Base
  # This is a model using the default database
  
  belongs_to :powerdns_record #...
  
  before_create :create_in_powerdns
  
private

  def create_in_powerdns
    unless create_powerdns_record(attrs)
      self.powerdns_error = "foo" # errors are returned from powerdns itself
      false
    end
  end
end

dns_template.rb

class DnsTemplate < ActiveRecord::Base
  # Another regular class
  
  has_many :dns_template_records
  
  def apply_to_domain(domain)
    DnsTemplate.transaction do
      dns_template_records.each { |rec| domain.dns_records.create!(rec.attributes) }
    end
  end
end

powerdns_record.rb

class PowerDNS::Record < PowerDNS::Base
  # this uses a database on an entirely different server
  # Nothing too fancy going on here
  
  has_one :dns_record #...
end