Exporting OpenTelemetry Metrics to Prometheus

What is Prometheus?

Prometheus is an open-source monitoring system with flexible query language and real-time alerting. It records metrics in a time series database using a HTTP pull model.

What is OpenTelemetry?

OpenTelemetry is an open source and vendor-neutral API for distributed tracing (including logs and errors) and metrics. With OpenTelemetry, you can instrument your application once and then add or change OpenTelemetry-compatible backends without changing the instrumentation.

OpenTelemetry Collector

What is OpenTelemetry Collector?

OpenTelemetry Collector is a proxy between your application and a backend that receives telemetry data, transforms it, and then exports to backends that can store the data permanently.

Collector can also act as an agent that pulls telemetry data from monitored systems, for example, Redis or filesystem metrics.

Exporting metrics to Prometheus

You can configure OpenTelemetry Collector to export data to Prometheus using Prometheus exporteropen in new window:

exporters:
  prometheus:
    endpoint: '1.2.3.4:1234'
    namespace: test-space
    const_labels:
      label1: value1
      'another label': spaced value
    send_timestamps: true
    metric_expiration: 180m
    resource_to_telemetry_conversion:
      enabled: true

OpenTelemetry Metrics

OpenTelemetry Go metrics

OpenTelemetry specifies how to collect, aggregate, and send metrics to backend platforms. Using OpenTelemetry instruments, you can create counter, gauge, and histogram metrics.

The simplest Counter instrument looks like this:

import "go.opentelemetry.io/otel/metric/instrument"

counter := Meter.SyncInt64().Counter(
	"test.my_counter",
    instrument.WithUnit("1"),
	instrument.WithDescription("Just a test counter"),
)

// Increment the counter.
counter.Add(ctx, 1, attribute.String("foo", "bar"))
counter.Add(ctx, 10, attribute.String("hello", "world"))

Sending Go metrics to Prometheus

To send OpenTelemetry Go metric to Prometheus, you need to provide a Prometheus target:

import (
	"go.opentelemetry.io/otel/exporters/prometheus"
	"go.opentelemetry.io/otel/metric/global"
	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
	"go.opentelemetry.io/otel/sdk/metric/aggregator/histogram"
	controller "go.opentelemetry.io/otel/sdk/metric/controller/basic"
	processor "go.opentelemetry.io/otel/sdk/metric/processor/basic"
	selector "go.opentelemetry.io/otel/sdk/metric/selector/simple"
)

func configureOpentelemetry() {
	exporter := configureMetrics()

	http.HandleFunc("/metrics", exporter.ServeHTTP)
	fmt.Println("listenening on http://localhost:8088/metrics")

	go func() {
		_ = http.ListenAndServe(":8088", nil)
	}()
}

func configureMetrics() *prometheus.Exporter {
	config := prometheus.Config{}

	ctrl := controller.New(
		processor.NewFactory(
			selector.NewWithHistogramDistribution(
				histogram.WithExplicitBoundaries(config.DefaultHistogramBoundaries),
			),
			export.CumulativeExportKindSelector(),
			processor.WithMemory(true),
		),
	)

	exporter, err := prometheus.New(config, ctrl)
	if err != nil {
		panic(err)
	}

	global.SetMeterProvider(exporter.MeterProvider())

	return exporter
}

And then configure Prometheus to scrape exposed metrics:

scrape_configs:
  - job_name: 'opentelemetry'
    static_configs:
      - targets: ['localhost:8088']

You can find a runnable example at GitHubopen in new window.

Exporting OpenTelemetry Metrics to Prometheus

# What is Prometheus?

# What is OpenTelemetry?

# OpenTelemetry Collector

# What is OpenTelemetry Collector?

# Exporting metrics to Prometheus

# OpenTelemetry Metrics

# OpenTelemetry Go metrics

# Sending Go metrics to Prometheus

# See also