How global a MeterProvider really is?

[ramonrrp]

Hi all!
searching for some help here! Sorry if this is not the best channel for this :)

According to docs, a meterProvider is essential to build instruments, and that's clear to me. Right after the initializing example of metric initialization, we have the topic aquiring a meter with this object.

Following this implementation in my tests i was note able to properly use meterProvider outside of the package where it's implemented (a package created to hold otel build and initialization code): I can acquire a meter with var meter = otel.Meter("example.io/package/name")(for example in a package main), build an instrument and call .Add method. But this metric were not been sent to my exporter (stdout)

My goal is to keep build and initialization codes in their own package of the application, so that i cann call this and acquire a meter in my package main. I guess that's a common situation

Is there a way to receive in a package a meter builded in another package or something in this line? Is this a nice practice? The doc brings that usually a MeterProvider is builded once and lives the time the app lives too. this has to be builded in the same package allways?

[dmathieu]

The global meter provider is not specific to one package. It is shared among the entire runtime of your application.
So yes, you can set a global meter provider in one package and reuse it in all the other ones.

If metrics are not exported properly, there must be another issue within your application. Are you able to setup a small reproduction example?

[ramonrrp]

Hi and Thanks @dmathieu!

Follow an example showing. Here is a main package trying to acquire and use a meter. Otel is initializated in the other package and this func is called in beggining of the execution

package main

import (
	"context"
	"localtest/other"

	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	otm "go.opentelemetry.io/otel/metric"
)

func main() {
	other.Test()

	mainMeter := otel.GetMeterProvider().Meter("localtest/other/myTestMeter")

	mainCounter, _ := mainMeter.Int64Counter(
		"temporary.call",
		otm.WithUnit("{call}"),
		otm.WithDescription("car counter"),
	)
	mainCounter.Add(context.Background(), 1, otm.WithAttributes(
		attribute.String("model", "Camaro"),
		attribute.Bool("IsCar", true),
	))

}

package other

import (
	"context"

	"log"
	"time"

	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/exporters/stdout/stdoutmetric"
	otm "go.opentelemetry.io/otel/metric"
	"go.opentelemetry.io/otel/sdk/metric"
	"go.opentelemetry.io/otel/sdk/resource"
	semconv "go.opentelemetry.io/otel/semconv/v1.26.0"
)

func Test() {
	res, err := newResource()
	if err != nil {
		panic(err)
	}
	meterProvider, err := newMeterProvider(res)
	if err != nil {
		panic(err)
	}

	defer func() {
		if err := meterProvider.Shutdown(context.Background()); err != nil {
			log.Println(err)
		}
	}()

	otel.SetMeterProvider(meterProvider)

	Meter := otel.Meter("myTestMeter")

	otherCounter, err := Meter.Int64Counter(
		"temporary.call",
		otm.WithUnit("{call}"),
		otm.WithDescription("car counter"),
	)
	otherCounter.Add(context.Background(), 1, otm.WithAttributes(
		attribute.String("model", "Monza"),
		attribute.Bool("IsCar", true),
	))

}

func newResource() (*resource.Resource, error) {
	return resource.Merge(resource.Default(),
		resource.NewWithAttributes(semconv.SchemaURL,
			semconv.ServiceName("my-service"),
			semconv.ServiceVersion("0.1.0"),
		))
}

func newMeterProvider(res *resource.Resource) (*metric.MeterProvider, error) {
	metricExporter, err := stdoutmetric.New()
	if err != nil {
		return nil, err
	}

	meterProvider := metric.NewMeterProvider(
		metric.WithResource(res),
		metric.WithReader(metric.NewPeriodicReader(metricExporter,
			// Default is 1m. Set to 3s for demonstrative purposes.
			metric.WithInterval(3*time.Second))),
	)
	return meterProvider, nil
}

Here the output that show only the counter generated in the same package where otel is initializated:

{"Resource":[{"Key":"service.name","Value":{"Type":"STRING","Value":"my-service"}},{"Key":"service.version","Value":{"Type":"STRING","Value":"0.1.0"}},{"Key":"telemetry.sdk.language","Value":{"Type":"STRING","Value":"go"}},{"Key":"telemetry.sdk.name","Value":{"Type":"STRING","Value":"opentelemetry"}},{"Key":"telemetry.sdk.version","Value":{"Type":"STRING","Value":"1.32.0"}}],"ScopeMetrics":[{"Scope":{"Name":"myTestMeter","Version":"","SchemaURL":"","Attributes":null},"Metrics":[{"Name":"temporary.call","Description":"car counter","Unit":"{call}","Data":{"DataPoints":[{"Attributes":[{"Key":"IsCar","Value":{"Type":"BOOL","Value":true}},{"Key":"model","Value":{"Type":"STRING","Value":"Monza"}}],"StartTime":"2024-11-20T07:40:23.831377979-03:00","Time":"2024-11-20T07:40:23.831517987-03:00","Value":1}],"Temporality":"CumulativeTemporality","IsMonotonic":true}}]}]}

[dmathieu]

defer func() {
		if err := meterProvider.Shutdown(context.Background()); err != nil {
			log.Println(err)
		}
	}()

You're shutting down this meter provider at the end of other.Test(), so in your main method, the meter provider won't log anything because it has been shut down already.
You need to shutdown only at the end of your entire program.

See this example for a way to do this: https://github.com/open-telemetry/opentelemetry-go-contrib/blob/main/examples/otel-collector/main.go#L89

[ramonrrp]

Hey @dmathieu i was able to reproduce this example and everything worked well!
Thanks a lot for this help! ❤️