Metrics feedback

[kaylareopelle]

We want your feedback on the opentelemetry-metrics-sdk and opentelemetry-metrics-api gems! Understanding how these libraries are used by the community will help us prioritize future work on Metrics.

[github-actions]

👋 This issue has been marked as stale because it has been open with no activity. You can: comment on the issue or remove the stale label to hold stale off for a while, add the keep label to hold stale off permanently, or do nothing. If you do nothing this issue will be closed eventually by the stale bot.

[chloe-meister]

Hi there 👋

I've started some prototype implementation of metrics in a Rails app, and I could get some metrics exported from the SDK example.

However, From the README it is not clear where and when I should pull the metrics and shutdown the provider?
These 2 lines:

OpenTelemetry.meter_provider.metric_readers.each(&:pull)
OpenTelemetry.meter_provider.shutdown

What we'd want to do is adding a counter metric each time a specific controller action is called. I can do this with a standard before_action filter, but from there I don't understand well when to pull the metrics from the reader? Any advice?

[kaylareopelle]

Hi @chloe-meister! Thanks for reaching out!

The README provides an example for a script that would run once, pull the metric, and exit the program.

If you're open to it, I think a periodic metric reader is a better fit for a Rails application. It'll collect the metrics and pass them to the exporter on a set interval. The process will live as long as the Rails application does, or until OpenTelemetry.meter_provider.shutdown is manually called.

Assuming you're using the OTLP exporter, rather than calling:

opentelemetry-ruby/examples/metrics_sdk/metrics_collect_otlp.rb

Lines 23 to 25 in 2f87a1d

	otlp_metric_exporter = OpenTelemetry::Exporter::OTLP::Metrics::MetricsExporter.new
	OpenTelemetry.meter_provider.add_metric_reader(otlp_metric_exporter)

You would call something like:

# config/initializers/opentelemetry.rb
reader = OpenTelemetry::SDK::Metrics::Export::PeriodicMetricReader.new(
          exporter: OpenTelemetry::Exporter::OTLP::Metrics::MetricsExporter.new,
          export_interval_millis: 3000,
          export_timeout_millis: 10000)

OpenTelemetry.meter_provider.add_metric_reader(reader)

You can create the meter and the counter the same way as in the example.
If you prefer the console exporter, just swap OpenTelemetry::Exporter::OTLP::Metrics::MetricsExporter with OpenTelemetry::SDK::Metrics::Export::ConsoleMetricPullExporter.

Using arguments above, your metrics would be exported every three seconds and would have a 10-second timeout.

Keep in mind that if you're using the OTLP exporter, you also need to install the opentelemetry-exporter-otlp-metrics gem.

[chloe-meister]

Hi @kaylareopelle! Thank you very much for the detailed answer. This helps a lot 🙏