# Money Trace Plugin¶

This is a remap plugin that allows ATS to participate in a distrbuted tracing system based upon the Comcast “Money” distributed tracing and monitoring library. The Comcast “Money” library has its roots in Google’s Dapper and Twitters Zipkin systems. A money trace header or session id, is attached to transaction and allows an operator with the appropriate logging systems in place, to determine where errors and/or latency may exit.

Use of the library enables the tracing of a transaction through all systems that participate in handling the request. See the documentation on this open source library at https://github.com/Comcast/money.

## How it Works¶

This plugin checks incoming requests for the “X-MoneyTrace” header. If the header is not present no further processing takes place. However if the header is present, the plugin will check to to see if the request has been cached. If so, the plugin will add the “X-Moneytrace” header from the incoming request to the cached response returned to the client as required by the money_trace protocol. If the request has not been cached, the plugin will extends the trace context by creating a new “X-MoneyTrace” header for inclusion in the outgoing request to a parent cache or origin server. The extended header includes the ‘trace-id’ from the incoming request, the incoming span-id becomes the outgoing parent-id and the plugin generates a new random long span id for the outgoing request. See the documentation at the link above for a complete description on the “X-MoneyTrace” header and how to use and extend it in a distributed tracing system.

## Installation¶

The Money Trace plugin is a remap plugin. Enable it by adding money_trace.so to your remap.config file. There are no options.

Here is an example remap.config entry:

map http://vod.foobar.com http://origin.vod.foobar.com @plugin=money_trace.so