Demos for IOLocal-based tracing with trace4cats

A small sample web service that calculates Fibonacci numbers using an inefficient, but parallel algorithm while producing spans. Demonstrates how tracing can be implemented using cats.effect.IOLocal and how the problem of root span creation could be handled (approach not tested yet).

Also included is a second example of a service that determines whether a number is even or odd by performing a mutual recursion with a twin service instance, decreasing the number by 1 each time. This demonstrates how tracing information can be passed and received via HTTP (using the W3C traceparent header).

Usage

Run the Fibonacci service

To run the service, use sbt:

sbt run

As this will not trigger any action other than starting the service and binding it to port 8080, request it via curl:

curl http://localhost:8080/6

The last path segment is the index of the Fibonacci number to calculate. Careful, higher numbers will create a huge amount of spans and take a while to complete (the computation is slowed down by sleeping in between to provide a real-world trace graph).

Run the even/odd services

To run the two services, open two shells and run

sbt runMain demo.even.Main one 8081 8082

and

sbt runMain demo.even.Main one 8082 8081

Then you can curl the first service like this

curl http://localhost:8080/even/6

It will check whether 6 is a recursion anchor (0 or 1) and if not, decrease by 1 one call the other service instance, that will perform the same and so on until an anchor is reached.

See the results

The service uses the Jaeger integration, so spin up a local instance to see the traces produced. See https://www.jaegertracing.io/docs/1.33/getting-started/ on how to do that, then open http://localhost:16686 in your browser.

Traces produced by the Fibonacci service will then look like this: