Tutorial - load balancing syslog messages by using protocol extensions

Syslog protocol available on the Citrix ADC appliance works only for the messages generated on the Citrix ADC appliance. It does not load balance the messages coming from external nodes. To load balance such messages, you need to use the protocol extensions feature and write the syslog message parsing logic by using the Lua 5.2 programming language.

Code for parsing syslog message

The code only has the TCP client data callback function defined - client.on_data(). For server data, it does not add a callback function and the server to client takes the fast native path. The code identifies message boundary based on the trailing character. If the TCP packet contains more than one syslog messages, then we split the packet based on the trailing character and load balance each message.


  Syslog event handler for TCP client data

    ctxt - TCP client side App processing context.

    data - TCP Data stream received.


function client.on_data(ctxt, payload)

                  local message = nil

                  local data_len

                  local data = payload.data

                  local trailing_character = "n"


                                    -- Get the offset of trailing character

                                    local new_line_character_offset = data:find(trailing_character)

                                    -- If trailing character is not found, then wait for more data.

                                    if (not new_line_character_offset) then

                                                      goto need_more_data


                                    -- Get the length of the current message

                                    data_len = data:len()

                                    -- Check whether we have more than one message

                                    -- by comparing trailing character offset and

                                    -- current data length

                                    if (data_len > new_line_character_offset) then

                                                      -- If we have more than one message, then split

                                                      -- the data into two parts such that first part

                                                      -- will contain message upto trailing character

                                                      -- offset and second part will contain

                                                      -- remaining message.

                                                      message, data = data:split(new_line_character_offset)


                                                      message = data

                                                      data = nil


-- Send the data to the backend server.

                                    ns.send(ctxt.output, "EOM", {data = message})

                                    goto done


                                                      -- Wait for more data


                                                      data = nil

                                                      goto done


                                                      -- If we have more data to parse,

                                                      -- then do parsing again.

                                                      if (data) then

                                                                        goto split_message



Tutorial - load balancing syslog messages by using protocol extensions