def app_servers
      ret = @servers.select { |s| s.nickname =~ /App Server/ }
      raise "No app servers in deployment" unless ret.length > 0
      ret
    end
def app_servers
      ret = @servers.select { |s| s.nickname =~ /App Server/ }
      raise "No app servers in deployment" unless ret.length > 0
      ret
    end
returns an Array of the App Servers in the deployment