feat: Add configuration patch to set metrics exporter by environment …

…variable

The environment variable has options for:
* console (default)
* otlp
* in-memory
* none

Like the Traces exporter, more than one exporter can be configured

metrics_sdk/lib/opentelemetry/sdk/metrics/configuration_patch.rb

@@ -10,12 +10,53 @@ module Metrics
       # The ConfiguratorPatch implements a hook to configure the metrics
       # portion of the SDK.
       module ConfiguratorPatch
+        def add_metric_reader(metric_reader)
+          @metric_readers << metric_reader
+        end
+
         private
 
+        def initialize
+          super
+          @metric_readers = []
+        end
+
         # The metrics_configuration_hook method is where we define the setup process
         # for metrics SDK.
         def metrics_configuration_hook
           OpenTelemetry.meter_provider = Metrics::MeterProvider.new(resource: @resource)
+          configure_metric_readers
+        end
+
+        def configure_metric_readers
+          readers = @metric_readers.empty? ? wrapped_metric_exporters_from_env.compact : @metric_readers
+          readers.each { |r| OpenTelemetry.meter_provider.add_metric_reader(r) }
+        end
+
+        def wrapped_metric_exporters_from_env
+          exporters = ENV.fetch('OTEL_METRICS_EXPORTER', 'console')
+
+          exporters.split(',').map do |exporter|
+            case exporter.strip
+            when 'none' then nil
+            when 'console'
+              OpenTelemetry.meter_provider.add_metric_reader(Metrics::Export::ConsoleMetricPullExporter.new)
+            when 'in-memory'
+              OpenTelemetry.meter_provider.add_metric_reader(Metrics::Export::InMemoryMetricPullExporter.new)
+            when 'otlp'
+              begin
+                OpenTelemetry.meter_provider.add_metric_reader(OpenTelemetry::Exporter::OTLP::MetricsExporter.new)
+              rescue NameError
+                OpenTelemetry.logger.warn 'The otlp metrics exporter cannot be configured - please add ' \
+                  'opentelemetry-exporter-otlp-metrics to your Gemfile, metrics will not be exported'
+                nil
+              end
+            else
+              OpenTelemetry.logger.warn "The #{exporter} exporter is unknown and cannot be configured, " \
+                'metrics will not be exported'
+              nil
+            end
+          end
         end
       end
     end

metrics_sdk/test/opentelemetry/sdk/metrics/configuration_patch_test.rb

@@ -0,0 +1,108 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+require 'test_helper'
+
+describe OpenTelemetry::SDK::Metrics::ConfiguratorPatch do
+  let(:configurator) { OpenTelemetry::SDK::Configurator.new }
+  let(:default_resource_attributes) do
+    {
+      'telemetry.sdk.name' => 'opentelemetry',
+      'telemetry.sdk.language' => 'ruby',
+      'telemetry.sdk.version' => OpenTelemetry::SDK::VERSION,
+      'process.pid' => Process.pid,
+      'process.command' => $PROGRAM_NAME,
+      'process.runtime.name' => RUBY_ENGINE,
+      'process.runtime.version' => RUBY_VERSION,
+      'process.runtime.description' => RUBY_DESCRIPTION,
+      'service.name' => 'unknown_service'
+    }
+  end
+
+  def setup
+    # Suppress log warnings about trace exporter absence
+    ENV['OTEL_TRACES_EXPORTER'] = 'none'
+  end
+
+  def teardown
+    # Let the settings go back to their default
+    ENV['OTEL_TRACES_EXPORTER'] = nil
+  end
+
+  describe '#configure' do
+    describe 'meter_provider' do
+      it 'is an instance of SDK::Metrics::MeterProvider' do
+        configurator.configure
+
+        _(OpenTelemetry.meter_provider).must_be_instance_of(
+          OpenTelemetry::SDK::Metrics::MeterProvider
+        )
+      end
+    end
+
+    describe 'metric readers' do
+      it 'defaults to the console reader' do
+        configurator.configure
+
+        assert_equal 1, OpenTelemetry.meter_provider.metric_readers.size
+        assert_instance_of OpenTelemetry::SDK::Metrics::Export::ConsoleMetricPullExporter, OpenTelemetry.meter_provider.metric_readers[0]
+      end
+
+      it 'can be set by environment variable' do
+        OpenTelemetry::TestHelpers.with_env('OTEL_METRICS_EXPORTER' => 'in-memory') do
+          configurator.configure
+        end
+
+        assert_equal 1, OpenTelemetry.meter_provider.metric_readers.size
+        assert_instance_of OpenTelemetry::SDK::Metrics::Export::InMemoryMetricPullExporter, OpenTelemetry.meter_provider.metric_readers[0]
+      end
+
+      it 'supports "none" as an environment variable' do
+        OpenTelemetry::TestHelpers.with_test_logger do |log_stream|
+          OpenTelemetry::TestHelpers.with_env('OTEL_METRICS_EXPORTER' => 'none') do
+            configurator.configure
+          end
+
+          assert_empty OpenTelemetry.meter_provider.metric_readers
+
+          refute_match(/The none exporter is unknown and cannot be configured/, log_stream.string)
+        end
+      end
+
+      it 'supports multiple exporters passed by environment variable' do
+        OpenTelemetry::TestHelpers.with_env('OTEL_METRICS_EXPORTER' => 'in-memory,console') do
+          configurator.configure
+        end
+
+        assert_equal 2, OpenTelemetry.meter_provider.metric_readers.size
+        assert_instance_of OpenTelemetry::SDK::Metrics::Export::InMemoryMetricPullExporter, OpenTelemetry.meter_provider.metric_readers[0]
+        assert_instance_of OpenTelemetry::SDK::Metrics::Export::ConsoleMetricPullExporter, OpenTelemetry.meter_provider.metric_readers[1]
+      end
+
+      it 'defaults to noop with invalid env var' do
+        OpenTelemetry::TestHelpers.with_test_logger do |log_stream|
+          OpenTelemetry::TestHelpers.with_env('OTEL_METRICS_EXPORTER' => 'unladen_swallow') do
+            configurator.configure
+          end
+
+          assert_empty OpenTelemetry.meter_provider.metric_readers
+          assert_match(/The unladen_swallow exporter is unknown and cannot be configured/, log_stream.string)
+        end
+      end
+
+      it 'rescues NameErrors when otlp set to env var and the library is not installed' do
+        OpenTelemetry::TestHelpers.with_test_logger do |log_stream|
+          OpenTelemetry::TestHelpers.with_env('OTEL_METRICS_EXPORTER' => 'otlp') do
+            configurator.configure
+          end
+
+          assert_empty OpenTelemetry.meter_provider.metric_readers
+          assert_match(/The otlp exporter cannot be configured - please add opentelemetry-exporter-otlp-metrics to your Gemfile, metrics will not be exported/, log_stream.string)
+        end
+      end
+    end
+  end
+end

metrics_sdk/test/opentelemetry/sdk/metrics/meter_provider_test.rb

@@ -9,7 +9,11 @@
 describe OpenTelemetry::SDK::Metrics::MeterProvider do
   before do
     reset_metrics_sdk
-    OpenTelemetry::SDK.configure
+    # The MeterProvider tests deal with mock MetricReaders that are manually added
+    # Run the tests without the configuration patch interfering with the setup
+    OpenTelemetry::TestHelpers.with_env('OTEL_METRICS_EXPORTER' => 'none') do
+      OpenTelemetry::SDK.configure
+    end
   end
 
   describe '#meter' do

metrics_sdk/test/test_helper.rb

@@ -33,3 +33,6 @@ def with_test_logger
 ensure
   OpenTelemetry.logger = original_logger
 end
+
+# Suppress warn-level logs about a missing OTLP exporter for traces
+ENV['OTEL_TRACES_EXPORTER'] = 'none'