otlp-demo

September 2025

This demo project shows how to use the Crystal language and Open Telemetry (OTLP) to send metrics and logs to both a local collector (Jaeger) and while running on Google Cloud Run. This repo is used to test out various ideas for a series of blog posts:

• https://medium.com/@nbrand01/instrumenting-a-crystal-program-with-otlp-571d5ae9348b

A Cloud Run service can only report custom OTLP metrics to Google Cloud Managed Service for Prometheus by using the Google-Built OpenTelemetry Collector as a sidecar. Logs and Traces are forwarded to Cloud Logging and Cloud Trace as expected.

There is a private preview of OTLP metrics on Google Cloud Monitoring. This preview only supports metrics, and not logs. I will experiment with it, and perhaps publish an updated blog regarding its features.

The crystal OTLP library was created by an engineer at New Relic, and wrote up a blog which is the basis of this repo. Based upon blog: https://medium.com/notes-and-tips-in-full-stack-development/how-to-begin-with-traces-in-crystal-2fd6a0255447

Installation

TODO: Write installation instructions here

Usage

TODO: Write usage instructions here

Development

Test

curl "http://127.0.0.1:8080/?n=37" curl -H "Authorization: Bearer $(gcloud auth print-identity-token)" https://otel-cloud-run-demo-161156519703.us-central1.run.app/?n=37

gcloud run services proxy otel-cloud-run-demo
--project testing-355714
--port 5000

crystal run src/load_generator.cr

Appendix and sources

Open Telemetry

• https://opentelemetry.io/
• https://opentelemetry.io/docs/languages/ruby/exporters/

New Relic blog and sources

• https://github.com/newrelic-experimental/mcv3-apps/blob/kh.add-crystal-example-20220412/Instrumented/crystal/src/fibonacci.cr
• https://github.com/wyhaines/opentelemetry-instrumentation.cr
• https://github.com/wyhaines/opentelemetry-sdk.cr
• https://github.com/wyhaines/opentelemetry-api.cr

Honeycomb OTLP library

• https://github.com/jgaskins/opentelemetry
• https://dev.to/fdocr/deploy-a-crystal-app-with-docker-and-opentelemetry-24cp

Jaeger

• https://www.jaegertracing.io/docs/next-release/deployment/

Contributing

1. Fork it (https://github.com/your-github-user/otlp-demo/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• Nick Brandaleone - creator and maintainer