ruby-telemetry

This is a minimal Ruby gem that provides a Telemetry::Method helper inspired by the Go package go-telemetry.

It supports three emitters chosen via environment variables:

• console — prints metric operations to stdout
• noop — no-op emitter
• prometheus — uses the prometheus-client gem and exposes metrics

Environment configuration (optional):

export METRICS_EMITTER=prometheus  # console | noop | prometheus
export METRICS_PREFIX=my_app_telemetry
export PROMETHEUS_ADDRESS=:8081

Quick example (script)

This example mirrors how the Go pkg/telemetry package is used: create a Method helper, record requests, latency and success/error counts.

require 'telemetry'

# initialize from ENV (auto-called on require; you can call explicitly)
Telemetry.init_from_env

# create a method helper (method name, service name)
m = Telemetry::Method.new('GetUser', 'UserService')

# count a request
m.count_request('path:/users')

# measure latency
start = Time.now
# ... do work ...
sleep 0.02
m.record_latency(start, 'path:/users')

# log error or success and increment counters accordingly
err = nil
m.log_and_count_error_or_success(err, 'path:/users')

# set a gauge
m.set_gauge(42.0, 'connections')

Rack exporter example

For web apps, the project includes a complete Rack demo in the examples/ folder.

Files added:

• examples/app.rb — a tiny Rack app that uses Telemetry::Method to emit counters, latency and gauges.
• examples/config.ru — mounts Telemetry::Emitter::ExporterMiddleware and runs the demo app.

Run the demo with the console emitter (default):

bundle exec rackup examples/config.ru -p 5123

Then exercise the app (in another terminal):

curl http://localhost:5123/      # app endpoint
curl http://localhost:5123/metrics # metrics endpoint (served by middleware)

Run the demo with the Prometheus emitter (starts a small server for metrics):

export METRICS_EMITTER=prometheus
export PROMETHEUS_ADDRESS=:8082  # optional
bundle exec rackup examples/config.ru -p 5123

Visit http://localhost:8082/metrics (or whichever address you set) to view prometheus-formatted metrics. You can still access the app at http://localhost:5123/.

Notes

• The prometheus-client gem is optional. If it's not installed the middleware and Prometheus emitter tests are skipped and the middleware will raise a NameError if invoked; install via bundle add prometheus-client or add it to your Gemfile if you plan to use Prometheus.
• Metric naming follows snake_case for service/method and uses dot-separated suffixes (e.g. my_app.my_service.my_method.latency).
• Latency is recorded in milliseconds to match the Go package; when using Prometheus histograms the emitter converts ms to seconds before observing.