diff --git a/exporter/otlp-metrics/lib/opentelemetry/exporter/otlp/metrics/metrics_exporter.rb b/exporter/otlp-metrics/lib/opentelemetry/exporter/otlp/metrics/metrics_exporter.rb
index d2beac6d53..d6d87921f6 100644
--- a/exporter/otlp-metrics/lib/opentelemetry/exporter/otlp/metrics/metrics_exporter.rb
+++ b/exporter/otlp-metrics/lib/opentelemetry/exporter/otlp/metrics/metrics_exporter.rb
@@ -26,7 +26,7 @@ module Exporter
     module OTLP
       module Metrics
         # An OpenTelemetry metrics exporter that sends metrics over HTTP as Protobuf encoded OTLP ExportMetricsServiceRequest.
-        class MetricsExporter < ::OpenTelemetry::SDK::Metrics::Export::MetricReader
+        class MetricsExporter < ::OpenTelemetry::SDK::Metrics::Export::MetricExporter
           include Util
 
           attr_reader :metric_snapshots
@@ -78,8 +78,8 @@ def initialize(endpoint: OpenTelemetry::Common::Utilities.config_opt('OTEL_EXPOR
           # consolidate the metrics data into the form of MetricData
           #
           # return MetricData
-          def pull
-            export(collect)
+          def pull(timeout: nil)
+            export(collect, timeout: timeout)
           end
 
           # metrics Array[MetricData]
diff --git a/exporter/otlp-metrics/test/opentelemetry/exporter/otlp/metrics/metrics_exporter_test.rb b/exporter/otlp-metrics/test/opentelemetry/exporter/otlp/metrics/metrics_exporter_test.rb
index 020d0e9a8d..ff192ac4be 100644
--- a/exporter/otlp-metrics/test/opentelemetry/exporter/otlp/metrics/metrics_exporter_test.rb
+++ b/exporter/otlp-metrics/test/opentelemetry/exporter/otlp/metrics/metrics_exporter_test.rb
@@ -336,6 +336,7 @@
 
   describe '#export' do
     let(:exporter) { OpenTelemetry::Exporter::OTLP::Metrics::MetricsExporter.new }
+    let(:metric_reader) { OpenTelemetry::SDK::Metrics::Export::MetricReader.new(exporter: exporter) }
     let(:meter_provider) { OpenTelemetry::SDK::Metrics::MeterProvider.new(resource: OpenTelemetry::SDK::Resources::Resource.telemetry_sdk) }
 
     it 'integrates with collector' do
@@ -530,11 +531,11 @@
 
     it 'exports a metric' do
       stub_post = stub_request(:post, 'http://localhost:4318/v1/metrics').to_return(status: 200)
-      meter_provider.add_metric_reader(exporter)
+      meter_provider.add_metric_reader(metric_reader)
       meter     = meter_provider.meter('test')
       counter   = meter.create_counter('test_counter', unit: 'smidgen', description: 'a small amount of something')
       counter.add(5, attributes: { 'foo' => 'bar' })
-      exporter.pull
+      metric_reader.pull
       meter_provider.shutdown
 
       assert_requested(stub_post)
@@ -574,7 +575,7 @@
 
     it 'translates all the things' do
       stub_request(:post, 'http://localhost:4318/v1/metrics').to_return(status: 200)
-      meter_provider.add_metric_reader(exporter)
+      meter_provider.add_metric_reader(metric_reader)
       meter   = meter_provider.meter('test')
 
       counter = meter.create_counter('test_counter', unit: 'smidgen', description: 'a small amount of something')
@@ -586,7 +587,7 @@
       gauge = meter.create_gauge('test_gauge', unit: 'smidgen', description: 'a small amount of something')
       gauge.record(15, attributes: { 'baz' => 'qux' })
 
-      exporter.pull
+      metric_reader.pull
       meter_provider.shutdown
 
       encoded_etsr = Opentelemetry::Proto::Collector::Metrics::V1::ExportMetricsServiceRequest.encode(
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/drop.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/drop.rb
index f638c649a5..a3290b6cce 100644
--- a/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/drop.rb
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/drop.rb
@@ -10,7 +10,7 @@ module Metrics
       module Aggregation
         # Contains the implementation of the Drop aggregation
         class Drop
-          attr_reader :aggregation_temporality
+          attr_accessor :aggregation_temporality
 
           def initialize(aggregation_temporality: :delta)
             @aggregation_temporality = aggregation_temporality
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/explicit_bucket_histogram.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/explicit_bucket_histogram.rb
index d379e0a9a4..2436c077ae 100644
--- a/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/explicit_bucket_histogram.rb
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/explicit_bucket_histogram.rb
@@ -14,7 +14,9 @@ class ExplicitBucketHistogram
           DEFAULT_BOUNDARIES = [0, 5, 10, 25, 50, 75, 100, 250, 500, 1000].freeze
           private_constant :DEFAULT_BOUNDARIES
 
-          attr_reader :aggregation_temporality
+          attr_accessor :aggregation_temporality
+
+          # attr_accessor :aggregation_temporality # approach 2
 
           # The default value for boundaries represents the following buckets:
           # (-inf, 0], (0, 5.0], (5.0, 10.0], (10.0, 25.0], (25.0, 50.0],
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/last_value.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/last_value.rb
index b2cffb74e2..dc48124f38 100644
--- a/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/last_value.rb
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/last_value.rb
@@ -10,7 +10,7 @@ module Metrics
       module Aggregation
         # Contains the implementation of the LastValue aggregation
         class LastValue
-          attr_reader :aggregation_temporality
+          attr_accessor :aggregation_temporality
 
           def initialize(aggregation_temporality: :delta)
             @aggregation_temporality = aggregation_temporality
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/sum.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/sum.rb
index c2771b38e3..fd41e044dd 100644
--- a/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/sum.rb
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/sum.rb
@@ -11,7 +11,7 @@ module Aggregation
         # Contains the implementation of the Sum aggregation
         # https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#sum-aggregation
         class Sum
-          attr_reader :aggregation_temporality
+          attr_accessor :aggregation_temporality
 
           def initialize(aggregation_temporality: ENV.fetch('OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE', :delta))
             # TODO: the default should be :cumulative, see issue #1555
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/configuration_patch.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/configuration_patch.rb
index f9ee2c07fa..cd1d74e670 100644
--- a/metrics_sdk/lib/opentelemetry/sdk/metrics/configuration_patch.rb
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/configuration_patch.rb
@@ -38,7 +38,7 @@ def wrapped_metric_exporters_from_env
             case exporter.strip
             when 'none' then nil
             when 'console' then OpenTelemetry.meter_provider.add_metric_reader(Metrics::Export::PeriodicMetricReader.new(exporter: Metrics::Export::ConsoleMetricPullExporter.new))
-            when 'in-memory' then OpenTelemetry.meter_provider.add_metric_reader(Metrics::Export::InMemoryMetricPullExporter.new)
+            when 'in-memory' then OpenTelemetry.meter_provider.add_metric_reader(Metrics::Export::MetricReader.new(exporter: Metrics::Export::InMemoryMetricPullExporter.new))
             when 'otlp'
               begin
                 OpenTelemetry.meter_provider.add_metric_reader(Metrics::Export::PeriodicMetricReader.new(exporter: OpenTelemetry::Exporter::OTLP::Metrics::MetricsExporter.new))
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/export.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/export.rb
index 782a75aae4..cd5ee075bf 100644
--- a/metrics_sdk/lib/opentelemetry/sdk/metrics/export.rb
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/export.rb
@@ -23,6 +23,7 @@ module Export
   end
 end
 
+require 'opentelemetry/sdk/metrics/export/metric_exporter'
 require 'opentelemetry/sdk/metrics/export/metric_reader'
 require 'opentelemetry/sdk/metrics/export/in_memory_metric_pull_exporter'
 require 'opentelemetry/sdk/metrics/export/console_metric_pull_exporter'
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/export/console_metric_pull_exporter.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/export/console_metric_pull_exporter.rb
index 8264c8e2e0..b23471a949 100644
--- a/metrics_sdk/lib/opentelemetry/sdk/metrics/export/console_metric_pull_exporter.rb
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/export/console_metric_pull_exporter.rb
@@ -11,16 +11,12 @@ module Export
         # Outputs {MetricData} to the console
         #
         # Potentially useful for exploratory purposes.
-        class ConsoleMetricPullExporter < MetricReader
+        class ConsoleMetricPullExporter < MetricExporter
           def initialize
             super
             @stopped = false
           end
 
-          def pull
-            export(collect)
-          end
-
           def export(metrics, timeout: nil)
             return FAILURE if @stopped
 
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/export/in_memory_metric_pull_exporter.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/export/in_memory_metric_pull_exporter.rb
index d0d8ccb902..6b6d529598 100644
--- a/metrics_sdk/lib/opentelemetry/sdk/metrics/export/in_memory_metric_pull_exporter.rb
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/export/in_memory_metric_pull_exporter.rb
@@ -10,7 +10,7 @@ module Metrics
       module Export
         # The InMemoryMetricPullExporter behaves as a Metric Reader and Exporter.
         # To be used for testing purposes, not production.
-        class InMemoryMetricPullExporter < MetricReader
+        class InMemoryMetricPullExporter < MetricExporter
           attr_reader :metric_snapshots
 
           def initialize
@@ -19,10 +19,6 @@ def initialize
             @mutex = Mutex.new
           end
 
-          def pull
-            export(collect)
-          end
-
           def export(metrics, timeout: nil)
             @mutex.synchronize do
               @metric_snapshots.concat(Array(metrics))
@@ -35,10 +31,6 @@ def reset
               @metric_snapshots.clear
             end
           end
-
-          def shutdown
-            SUCCESS
-          end
         end
       end
     end
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/export/metric_exporter.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/export/metric_exporter.rb
new file mode 100644
index 0000000000..e384ee49b6
--- /dev/null
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/export/metric_exporter.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+module OpenTelemetry
+  module SDK
+    module Metrics
+      module Export
+        # Exporter provides a minimal example implementation.
+        # It is not required to subclass this class to provide an implementation
+        # of MetricReader, provided the interface is satisfied.
+        class MetricExporter
+          attr_reader :metric_store
+
+          def initialize
+            @metric_store = OpenTelemetry::SDK::Metrics::State::MetricStore.new
+          end
+
+          def collect
+            @metric_store.collect
+          end
+
+          def pull(timeout: nil)
+            export(collect, timeout: timeout)
+          end
+
+          def export(metrics, timeout: nil)
+            Export::SUCCESS
+          end
+
+          def shutdown(timeout: nil)
+            Export::SUCCESS
+          end
+
+          def force_flush(timeout: nil)
+            Export::SUCCESS
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/export/metric_reader.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/export/metric_reader.rb
index c261f4f10a..4f85fa250b 100644
--- a/metrics_sdk/lib/opentelemetry/sdk/metrics/export/metric_reader.rb
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/export/metric_reader.rb
@@ -8,26 +8,69 @@ module OpenTelemetry
   module SDK
     module Metrics
       module Export
-        # MetricReader provides a minimal example implementation.
-        # It is not required to subclass this class to provide an implementation
-        # of MetricReader, provided the interface is satisfied.
+        # MetricReader
         class MetricReader
-          attr_reader :metric_store
+          attr_reader :exporters
 
-          def initialize
-            @metric_store = OpenTelemetry::SDK::Metrics::State::MetricStore.new
+          def initialize(exporter: nil)
+            @mutex = Mutex.new
+            @exporters = []
+            register_exporter(exporter: exporter)
           end
 
-          def collect
-            @metric_store.collect
+          # The metrics Reader implementation supports registering metric Exporters
+          def register_exporter(exporter: nil)
+            return unless exporter.respond_to?(:pull)
+
+            @mutex.synchronize do
+              @exporters << exporter
+            end
+          end
+
+          # exporter pull should trigger exporter to send out the metrics
+          def collect(timeout: nil)
+            @exporters.each { |exporter| exporter.pull(timeout: timeout) if exporter.respond_to?(:pull) }
+          end
+          alias pull collect
+
+          # The metrics Reader implementation supports configuring the
+          # default aggregation on the basis of instrument kind.
+          def aggregator(aggregator: nil, instrument_kind: nil)
+            return if aggregator.nil?
+
+            @exporters.each do |exporter|
+              exporter.metric_store.metric_streams.each do |ms|
+                ms.default_aggregation = aggregator if instrument_kind.nil? || ms.instrument_kind == instrument_kind
+              end
+            end
+          end
+
+          # The metrics Reader implementation supports configuring the
+          # default temporality on the basis of instrument kind.
+          def temporality(temporality: nil, instrument_kind: nil)
+            return if temporality.nil?
+
+            @exporters.each do |exporter|
+              exporter.metric_store.metric_streams.each do |ms|
+                ms.default_aggregation.aggregation_temporality = temporality if instrument_kind.nil? || ms.instrument_kind == instrument_kind
+              end
+            end
           end
 
+          # shutdown all exporters
           def shutdown(timeout: nil)
+            @exporters.each { |exporter| exporter.shutdown(timeout: timeout) if exporter.respond_to?(:shutdown) }
             Export::SUCCESS
+          rescue StandardError
+            Export::FAILURE
           end
 
+          # force flush all exporters
           def force_flush(timeout: nil)
+            @exporters.each { |exporter| exporter.force_flush(timeout: timeout) if exporter.respond_to?(:force_flush) }
             Export::SUCCESS
+          rescue StandardError
+            Export::FAILURE
           end
         end
       end
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/export/periodic_metric_reader.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/export/periodic_metric_reader.rb
index 948f98976c..97ccdd84b5 100644
--- a/metrics_sdk/lib/opentelemetry/sdk/metrics/export/periodic_metric_reader.rb
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/export/periodic_metric_reader.rb
@@ -25,14 +25,12 @@ class PeriodicMetricReader < MetricReader
           def initialize(export_interval_millis: Float(ENV.fetch('OTEL_METRIC_EXPORT_INTERVAL', 60_000)),
                          export_timeout_millis: Float(ENV.fetch('OTEL_METRIC_EXPORT_TIMEOUT', 30_000)),
                          exporter: nil)
-            super()
+            super(exporter: exporter)
 
             @export_interval = export_interval_millis / 1000.0
             @export_timeout = export_timeout_millis / 1000.0
-            @exporter = exporter
             @thread   = nil
             @continue = false
-            @mutex = Mutex.new
             @export_mutex = Mutex.new
 
             start
@@ -44,26 +42,21 @@ def shutdown(timeout: nil)
               @thread
             end
             thread&.join(@export_interval)
-            @exporter.force_flush if @exporter.respond_to?(:force_flush)
-            @exporter.shutdown
-            Export::SUCCESS
+            super(timeout: timeout)
           rescue StandardError => e
             OpenTelemetry.handle_error(exception: e, message: 'Fail to shutdown PeriodicMetricReader.')
             Export::FAILURE
           end
 
           def force_flush(timeout: nil)
-            export(timeout: timeout)
-            Export::SUCCESS
-          rescue StandardError
-            Export::FAILURE
+            super(timeout: timeout)
           end
 
           private
 
           def start
             @continue = true
-            if @exporter.nil?
+            if @exporters.empty?
               OpenTelemetry.logger.warn 'Missing exporter in PeriodicMetricReader.'
             elsif @thread&.alive?
               OpenTelemetry.logger.warn 'PeriodicMetricReader is still running. Please shutdown it if it needs to restart.'
@@ -85,8 +78,7 @@ def start
 
           def export(timeout: nil)
             @export_mutex.synchronize do
-              collected_metrics = collect
-              @exporter.export(collected_metrics, timeout: timeout || @export_timeout) unless collected_metrics.empty?
+              @exporters.each { |exporter| exporter.pull(timeout: timeout || @export_timeout) if exporter.respond_to?(:pull) }
             end
           end
 
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/meter.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/meter.rb
index dee8fea8d2..a85e7154d7 100644
--- a/metrics_sdk/lib/opentelemetry/sdk/metrics/meter.rb
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/meter.rb
@@ -31,7 +31,9 @@ def initialize(name, version, meter_provider)
         # @api private
         def add_metric_reader(metric_reader)
           @instrument_registry.each_value do |instrument|
-            instrument.register_with_new_metric_store(metric_reader.metric_store)
+            metric_reader.exporters.each do |exporter|
+              instrument.register_with_new_metric_store(exporter.metric_store)
+            end
           end
         end
 
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/meter_provider.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/meter_provider.rb
index 4538a88db4..2ced47279f 100644
--- a/metrics_sdk/lib/opentelemetry/sdk/metrics/meter_provider.rb
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/meter_provider.rb
@@ -122,7 +122,9 @@ def add_metric_reader(metric_reader)
         def register_synchronous_instrument(instrument)
           @mutex.synchronize do
             @metric_readers.each do |mr|
-              instrument.register_with_new_metric_store(mr.metric_store)
+              mr.exporters.each do |exporter|
+                instrument.register_with_new_metric_store(exporter.metric_store)
+              end
             end
           end
         end
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/state/metric_store.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/state/metric_store.rb
index b89eb09161..6d7ac5bb5b 100644
--- a/metrics_sdk/lib/opentelemetry/sdk/metrics/state/metric_store.rb
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/state/metric_store.rb
@@ -13,6 +13,8 @@ module State
         # The MetricStore module provides SDK internal functionality that is not a part of the
         # public API.
         class MetricStore
+          attr_reader :metric_streams
+
           def initialize
             @mutex = Mutex.new
             @epoch_start_time = now_in_nano
@@ -23,7 +25,6 @@ def initialize
           def collect
             @mutex.synchronize do
               @epoch_end_time = now_in_nano
-              # snapshot = @metric_streams.map { |ms| ms.collect(@epoch_start_time, @epoch_end_time) }
               snapshot = @metric_streams.flat_map { |ms| ms.collect(@epoch_start_time, @epoch_end_time) }
               @epoch_start_time = @epoch_end_time
               snapshot
diff --git a/metrics_sdk/lib/opentelemetry/sdk/metrics/state/metric_stream.rb b/metrics_sdk/lib/opentelemetry/sdk/metrics/state/metric_stream.rb
index 05033f522c..d5aaf47416 100644
--- a/metrics_sdk/lib/opentelemetry/sdk/metrics/state/metric_stream.rb
+++ b/metrics_sdk/lib/opentelemetry/sdk/metrics/state/metric_stream.rb
@@ -14,6 +14,7 @@ module State
         # public API.
         class MetricStream
           attr_reader :name, :description, :unit, :instrument_kind, :instrumentation_scope, :data_points
+          attr_accessor :default_aggregation
 
           def initialize(
             name,
diff --git a/metrics_sdk/test/integration/in_memory_metric_pull_exporter_test.rb b/metrics_sdk/test/integration/in_memory_metric_pull_exporter_test.rb
index 3e060e79dc..18f26b55f5 100644
--- a/metrics_sdk/test/integration/in_memory_metric_pull_exporter_test.rb
+++ b/metrics_sdk/test/integration/in_memory_metric_pull_exporter_test.rb
@@ -14,7 +14,8 @@
       OpenTelemetry::SDK.configure
 
       metric_exporter = OpenTelemetry::SDK::Metrics::Export::InMemoryMetricPullExporter.new
-      OpenTelemetry.meter_provider.add_metric_reader(metric_exporter)
+      metric_reader = OpenTelemetry::SDK::Metrics::Export::MetricReader.new(exporter: metric_exporter)
+      OpenTelemetry.meter_provider.add_metric_reader(metric_reader)
 
       meter = OpenTelemetry.meter_provider.meter('test')
       counter = meter.create_counter('counter', unit: 'smidgen', description: 'a small amount of something')
@@ -25,7 +26,7 @@
       counter.add(3, attributes: { 'b' => 'c' })
       counter.add(4, attributes: { 'd' => 'e' })
 
-      metric_exporter.pull
+      metric_reader.pull
       last_snapshot = metric_exporter.metric_snapshots
 
       _(last_snapshot).wont_be_empty
diff --git a/metrics_sdk/test/integration/metric_exporter_test.rb b/metrics_sdk/test/integration/metric_exporter_test.rb
new file mode 100644
index 0000000000..f93036da3b
--- /dev/null
+++ b/metrics_sdk/test/integration/metric_exporter_test.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+require_relative '../test_helper'
+
+describe OpenTelemetry::SDK do
+  describe '#metric_exporter' do
+    export = OpenTelemetry::SDK::Metrics::Export
+    let(:exporter) { export::MetricExporter.new }
+
+    it 'verify basic exporter function' do
+      _(exporter.export(nil)).must_equal export::SUCCESS
+      _(exporter.shutdown).must_equal export::SUCCESS
+      _(exporter.force_flush).must_equal export::SUCCESS
+      _(exporter.collect).must_equal []
+    end
+  end
+end
diff --git a/metrics_sdk/test/integration/metric_reader_test.rb b/metrics_sdk/test/integration/metric_reader_test.rb
new file mode 100644
index 0000000000..db506dbc07
--- /dev/null
+++ b/metrics_sdk/test/integration/metric_reader_test.rb
@@ -0,0 +1,92 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+require_relative '../test_helper'
+
+describe OpenTelemetry::SDK do
+  describe '#metric_reader' do
+    export = OpenTelemetry::SDK::Metrics::Export
+    let(:exporter) { export::ConsoleMetricPullExporter.new }
+
+    before do
+      reset_metrics_sdk
+      ENV['OTEL_METRICS_EXPORTER'] = 'none'
+
+      @metric_reader = export::MetricReader.new(exporter: exporter)
+
+      OpenTelemetry::SDK.configure
+      OpenTelemetry.meter_provider.add_metric_reader(@metric_reader)
+
+      meter = OpenTelemetry.meter_provider.meter('test_1')
+      @counter = meter.create_counter('counter_1', unit: 'smidgen', description: 'a small amount of something')
+    end
+
+    after do
+      ENV.delete('OTEL_METRICS_EXPORTER')
+    end
+
+    it 'initialize metric_reader' do
+      metric_reader = export::MetricReader.new(exporter: exporter)
+      _(metric_reader.exporters.first.class).must_equal export::ConsoleMetricPullExporter
+    end
+
+    it 'register additional metric_exporter' do
+      metric_reader = export::MetricReader.new(exporter: exporter)
+      in_memory_exporter = export::InMemoryMetricPullExporter.new
+      metric_reader.register_exporter(exporter: in_memory_exporter)
+      _(metric_reader.exporters[0].class).must_equal export::ConsoleMetricPullExporter
+      _(metric_reader.exporters[1].class).must_equal export::InMemoryMetricPullExporter
+    end
+
+    it 'change default aggregator' do
+      default_aggregation = @counter.instance_variable_get(:@metric_streams).first.default_aggregation
+
+      _(default_aggregation.class).must_equal OpenTelemetry::SDK::Metrics::Aggregation::Sum
+      _(default_aggregation.aggregation_temporality).must_equal :delta
+
+      @metric_reader.aggregator(aggregator: OpenTelemetry::SDK::Metrics::Aggregation::Drop.new)
+
+      default_aggregation = @counter.instance_variable_get(:@metric_streams).first.default_aggregation
+      _(default_aggregation.class).must_equal OpenTelemetry::SDK::Metrics::Aggregation::Drop
+    end
+
+    it 'do not change default aggregator if different instrument kind' do
+      default_aggregation = @counter.instance_variable_get(:@metric_streams).first.default_aggregation
+
+      _(default_aggregation.class).must_equal OpenTelemetry::SDK::Metrics::Aggregation::Sum
+      _(default_aggregation.aggregation_temporality).must_equal :delta
+
+      @metric_reader.aggregator(aggregator: OpenTelemetry::SDK::Metrics::Aggregation::Drop.new, instrument_kind: :gauge)
+
+      default_aggregation = @counter.instance_variable_get(:@metric_streams).first.default_aggregation
+      _(default_aggregation.class).must_equal OpenTelemetry::SDK::Metrics::Aggregation::Sum
+    end
+
+    it 'change default aggregation_temporality' do
+      default_aggregation = @counter.instance_variable_get(:@metric_streams).first.default_aggregation
+
+      _(default_aggregation.class).must_equal OpenTelemetry::SDK::Metrics::Aggregation::Sum
+      _(default_aggregation.aggregation_temporality).must_equal :delta
+
+      @metric_reader.temporality(temporality: :cumulative)
+
+      default_aggregation = @counter.instance_variable_get(:@metric_streams).first.default_aggregation
+      _(default_aggregation.aggregation_temporality).must_equal :cumulative
+    end
+
+    it 'do not change default aggregation_temporality if different instrument kind' do
+      default_aggregation = @counter.instance_variable_get(:@metric_streams).first.default_aggregation
+
+      _(default_aggregation.class).must_equal OpenTelemetry::SDK::Metrics::Aggregation::Sum
+      _(default_aggregation.aggregation_temporality).must_equal :delta
+
+      @metric_reader.temporality(temporality: :cumulative, instrument_kind: :gauge)
+
+      default_aggregation = @counter.instance_variable_get(:@metric_streams).first.default_aggregation
+      _(default_aggregation.aggregation_temporality).must_equal :delta
+    end
+  end
+end
diff --git a/metrics_sdk/test/opentelemetry/sdk/metrics/configuration_patch_test.rb b/metrics_sdk/test/opentelemetry/sdk/metrics/configuration_patch_test.rb
index 88cd4bdaa0..437db2eeb1 100644
--- a/metrics_sdk/test/opentelemetry/sdk/metrics/configuration_patch_test.rb
+++ b/metrics_sdk/test/opentelemetry/sdk/metrics/configuration_patch_test.rb
@@ -44,7 +44,7 @@
         reader = OpenTelemetry.meter_provider.metric_readers[0]
 
         assert_instance_of OpenTelemetry::SDK::Metrics::Export::PeriodicMetricReader, reader
-        assert_instance_of OpenTelemetry::Exporter::OTLP::Metrics::MetricsExporter, reader.instance_variable_get(:@exporter)
+        assert_instance_of OpenTelemetry::Exporter::OTLP::Metrics::MetricsExporter, reader.exporters.first
       end
 
       it 'can be set by environment variable' do
@@ -57,7 +57,7 @@
         reader = OpenTelemetry.meter_provider.metric_readers[0]
 
         assert_instance_of OpenTelemetry::SDK::Metrics::Export::PeriodicMetricReader, reader
-        assert_instance_of OpenTelemetry::SDK::Metrics::Export::ConsoleMetricPullExporter, reader.instance_variable_get(:@exporter)
+        assert_instance_of OpenTelemetry::SDK::Metrics::Export::ConsoleMetricPullExporter, reader.exporters.first
       end
 
       it 'supports "none" as an environment variable' do
@@ -83,9 +83,9 @@
         reader2 = OpenTelemetry.meter_provider.metric_readers[1]
 
         assert_instance_of OpenTelemetry::SDK::Metrics::Export::PeriodicMetricReader, reader1
-        assert_instance_of OpenTelemetry::SDK::Metrics::Export::ConsoleMetricPullExporter, reader1.instance_variable_get(:@exporter)
+        assert_instance_of OpenTelemetry::SDK::Metrics::Export::ConsoleMetricPullExporter, reader1.exporters.first
 
-        assert_instance_of OpenTelemetry::SDK::Metrics::Export::InMemoryMetricPullExporter, reader2
+        assert_instance_of OpenTelemetry::SDK::Metrics::Export::InMemoryMetricPullExporter, reader2.exporters.first
       end
 
       it 'defaults to noop with invalid env var' do
diff --git a/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/counter_test.rb b/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/counter_test.rb
index ff5c3edfe2..289f25b3d6 100644
--- a/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/counter_test.rb
+++ b/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/counter_test.rb
@@ -8,18 +8,19 @@
 
 describe OpenTelemetry::SDK::Metrics::Instrument::Counter do
   let(:metric_exporter) { OpenTelemetry::SDK::Metrics::Export::InMemoryMetricPullExporter.new }
+  let(:metric_reader) { OpenTelemetry::SDK::Metrics::Export::MetricReader.new(exporter: metric_exporter) }
   let(:meter) { OpenTelemetry.meter_provider.meter('test') }
   let(:counter) { meter.create_counter('counter', unit: 'smidgen', description: 'a small amount of something') }
 
   before do
     reset_metrics_sdk
     OpenTelemetry::SDK.configure
-    OpenTelemetry.meter_provider.add_metric_reader(metric_exporter)
+    OpenTelemetry.meter_provider.add_metric_reader(metric_reader)
   end
 
   it 'counts' do
     counter.add(1, attributes: { 'foo' => 'bar' })
-    metric_exporter.pull
+    metric_reader.pull
     last_snapshot = metric_exporter.metric_snapshots
 
     _(last_snapshot[0].name).must_equal('counter')
diff --git a/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/gauge_test.rb b/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/gauge_test.rb
index f3fc5509c6..76c60cefc0 100644
--- a/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/gauge_test.rb
+++ b/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/gauge_test.rb
@@ -8,18 +8,19 @@
 
 describe OpenTelemetry::SDK::Metrics::Instrument::Gauge do
   let(:metric_exporter) { OpenTelemetry::SDK::Metrics::Export::InMemoryMetricPullExporter.new }
+  let(:metric_reader) { OpenTelemetry::SDK::Metrics::Export::MetricReader.new(exporter: metric_exporter) }
   let(:meter) { OpenTelemetry.meter_provider.meter('test') }
   let(:gauge) { meter.create_gauge('gauge', unit: 'smidgen', description: 'a small amount of something') }
 
   before do
     reset_metrics_sdk
     OpenTelemetry::SDK.configure
-    OpenTelemetry.meter_provider.add_metric_reader(metric_exporter)
+    OpenTelemetry.meter_provider.add_metric_reader(metric_reader)
   end
 
   it 'gauge should count -2' do
     gauge.record(-2, attributes: { 'foo' => 'bar' })
-    metric_exporter.pull
+    metric_reader.pull
     last_snapshot = metric_exporter.metric_snapshots
 
     _(last_snapshot[0].name).must_equal('gauge')
@@ -34,7 +35,7 @@
   it 'gauge should count 1 for last recording' do
     gauge.record(-2, attributes: { 'foo' => 'bar' })
     gauge.record(1, attributes: { 'foo' => 'bar' })
-    metric_exporter.pull
+    metric_reader.pull
     last_snapshot = metric_exporter.metric_snapshots
 
     _(last_snapshot.size).must_equal(1)
@@ -48,7 +49,7 @@
     gauge2 = meter.create_gauge('gauge2', unit: 'smidgen', description: 'a small amount of something')
     gauge2.record(10, attributes: {})
 
-    metric_exporter.pull
+    metric_reader.pull
     last_snapshot = metric_exporter.metric_snapshots
 
     _(last_snapshot.size).must_equal(2)
diff --git a/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/histogram_test.rb b/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/histogram_test.rb
index 771ffaef83..65d7ce48a0 100644
--- a/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/histogram_test.rb
+++ b/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/histogram_test.rb
@@ -8,19 +8,20 @@
 
 describe OpenTelemetry::SDK::Metrics::Instrument::Histogram do
   let(:metric_exporter) { OpenTelemetry::SDK::Metrics::Export::InMemoryMetricPullExporter.new }
+  let(:metric_reader) { OpenTelemetry::SDK::Metrics::Export::MetricReader.new(exporter: metric_exporter) }
   let(:meter) { OpenTelemetry.meter_provider.meter('test') }
   let(:histogram) { meter.create_histogram('histogram', unit: 'smidgen', description: 'a small amount of something') }
 
   before do
     reset_metrics_sdk
     OpenTelemetry::SDK.configure
-    OpenTelemetry.meter_provider.add_metric_reader(metric_exporter)
+    OpenTelemetry.meter_provider.add_metric_reader(metric_reader)
   end
 
   it 'histograms' do
     histogram.record(5, attributes: { 'foo' => 'bar' })
     histogram.record(6, attributes: { 'foo' => 'bar' })
-    metric_exporter.pull
+    metric_reader.pull
     last_snapshot = metric_exporter.metric_snapshots
 
     _(last_snapshot[0].name).must_equal('histogram')
diff --git a/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/up_down_counter_test.rb b/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/up_down_counter_test.rb
index 687ad27a89..3a6ddca642 100644
--- a/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/up_down_counter_test.rb
+++ b/metrics_sdk/test/opentelemetry/sdk/metrics/instrument/up_down_counter_test.rb
@@ -8,19 +8,20 @@
 
 describe OpenTelemetry::SDK::Metrics::Instrument::UpDownCounter do
   let(:metric_exporter) { OpenTelemetry::SDK::Metrics::Export::InMemoryMetricPullExporter.new }
+  let(:metric_reader) { OpenTelemetry::SDK::Metrics::Export::MetricReader.new(exporter: metric_exporter) }
   let(:meter) { OpenTelemetry.meter_provider.meter('test') }
   let(:up_down_counter) { meter.create_up_down_counter('up_down_counter', unit: 'smidgen', description: 'a small amount of something') }
 
   before do
     reset_metrics_sdk
     OpenTelemetry::SDK.configure
-    OpenTelemetry.meter_provider.add_metric_reader(metric_exporter)
+    OpenTelemetry.meter_provider.add_metric_reader(metric_reader)
   end
 
   it 'counts up and down' do
     up_down_counter.add(1, attributes: { 'foo' => 'bar' })
     up_down_counter.add(-2, attributes: { 'foo' => 'bar' })
-    metric_exporter.pull
+    metric_reader.pull
     last_snapshot = metric_exporter.metric_snapshots
 
     _(last_snapshot[0].name).must_equal('up_down_counter')
diff --git a/metrics_sdk/test/opentelemetry/sdk/metrics/meter_provider_test.rb b/metrics_sdk/test/opentelemetry/sdk/metrics/meter_provider_test.rb
index 72f04e08c9..83e72daf65 100644
--- a/metrics_sdk/test/opentelemetry/sdk/metrics/meter_provider_test.rb
+++ b/metrics_sdk/test/opentelemetry/sdk/metrics/meter_provider_test.rb
@@ -112,29 +112,33 @@
     it 'associates the metric store with instruments created before the metric reader' do
       meter_a = OpenTelemetry.meter_provider.meter('a').create_counter('meter_a')
 
-      metric_reader_a = OpenTelemetry::SDK::Metrics::Export::MetricReader.new
+      metric_exporter_a = OpenTelemetry::SDK::Metrics::Export::MetricExporter.new
+      metric_reader_a = OpenTelemetry::SDK::Metrics::Export::MetricReader.new(exporter: metric_exporter_a)
       OpenTelemetry.meter_provider.add_metric_reader(metric_reader_a)
 
-      metric_reader_b = OpenTelemetry::SDK::Metrics::Export::MetricReader.new
+      metric_exporter_b = OpenTelemetry::SDK::Metrics::Export::MetricExporter.new
+      metric_reader_b = OpenTelemetry::SDK::Metrics::Export::MetricReader.new(exporter: metric_exporter_b)
       OpenTelemetry.meter_provider.add_metric_reader(metric_reader_b)
 
       _(meter_a.instance_variable_get(:@metric_streams).size).must_equal(2)
-      _(metric_reader_a.metric_store.instance_variable_get(:@metric_streams).size).must_equal(1)
-      _(metric_reader_b.metric_store.instance_variable_get(:@metric_streams).size).must_equal(1)
+      _(metric_reader_a.exporters.first.metric_store.instance_variable_get(:@metric_streams).size).must_equal(1)
+      _(metric_reader_b.exporters.first.metric_store.instance_variable_get(:@metric_streams).size).must_equal(1)
     end
 
     it 'associates the metric store with instruments created after the metric reader' do
-      metric_reader_a = OpenTelemetry::SDK::Metrics::Export::MetricReader.new
+      metric_exporter_a = OpenTelemetry::SDK::Metrics::Export::MetricExporter.new
+      metric_reader_a = OpenTelemetry::SDK::Metrics::Export::MetricReader.new(exporter: metric_exporter_a)
       OpenTelemetry.meter_provider.add_metric_reader(metric_reader_a)
 
-      metric_reader_b = OpenTelemetry::SDK::Metrics::Export::MetricReader.new
+      metric_exporter_b = OpenTelemetry::SDK::Metrics::Export::MetricExporter.new
+      metric_reader_b = OpenTelemetry::SDK::Metrics::Export::MetricReader.new(exporter: metric_exporter_b)
       OpenTelemetry.meter_provider.add_metric_reader(metric_reader_b)
 
       meter_a = OpenTelemetry.meter_provider.meter('a').create_counter('meter_a')
 
       _(meter_a.instance_variable_get(:@metric_streams).size).must_equal(2)
-      _(metric_reader_a.metric_store.instance_variable_get(:@metric_streams).size).must_equal(1)
-      _(metric_reader_b.metric_store.instance_variable_get(:@metric_streams).size).must_equal(1)
+      _(metric_reader_a.exporters.first.metric_store.instance_variable_get(:@metric_streams).size).must_equal(1)
+      _(metric_reader_b.exporters.first.metric_store.instance_variable_get(:@metric_streams).size).must_equal(1)
     end
   end
 
diff --git a/metrics_sdk/test/opentelemetry/sdk/metrics/view/registered_view_test.rb b/metrics_sdk/test/opentelemetry/sdk/metrics/view/registered_view_test.rb
index 4638485777..fb70f5119e 100644
--- a/metrics_sdk/test/opentelemetry/sdk/metrics/view/registered_view_test.rb
+++ b/metrics_sdk/test/opentelemetry/sdk/metrics/view/registered_view_test.rb
@@ -14,7 +14,8 @@
       OpenTelemetry::SDK.configure
 
       metric_exporter = OpenTelemetry::SDK::Metrics::Export::InMemoryMetricPullExporter.new
-      OpenTelemetry.meter_provider.add_metric_reader(metric_exporter)
+      metric_reader = OpenTelemetry::SDK::Metrics::Export::MetricReader.new(exporter: metric_exporter)
+      OpenTelemetry.meter_provider.add_metric_reader(metric_reader)
 
       meter = OpenTelemetry.meter_provider.meter('test')
       OpenTelemetry.meter_provider.add_view('counter', aggregation: ::OpenTelemetry::SDK::Metrics::Aggregation::Drop.new)
@@ -24,7 +25,7 @@
       counter.add(1)
       counter.add(2, attributes: { 'a' => 'b' })
 
-      metric_exporter.pull
+      metric_reader.pull
       last_snapshot = metric_exporter.metric_snapshots
 
       _(last_snapshot).wont_be_empty
@@ -47,7 +48,8 @@
       OpenTelemetry::SDK.configure
 
       metric_exporter = OpenTelemetry::SDK::Metrics::Export::InMemoryMetricPullExporter.new
-      OpenTelemetry.meter_provider.add_metric_reader(metric_exporter)
+      metric_reader = OpenTelemetry::SDK::Metrics::Export::MetricReader.new(exporter: metric_exporter)
+      OpenTelemetry.meter_provider.add_metric_reader(metric_reader)
 
       meter = OpenTelemetry.meter_provider.meter('test')
       OpenTelemetry.meter_provider.add_view('counter', aggregation: ::OpenTelemetry::SDK::Metrics::Aggregation::LastValue.new)
@@ -59,7 +61,7 @@
       counter.add(3)
       counter.add(4)
 
-      metric_exporter.pull
+      metric_reader.pull
       last_snapshot = metric_exporter.metric_snapshots
 
       _(last_snapshot[0].data_points).wont_be_empty
@@ -70,7 +72,8 @@
       OpenTelemetry::SDK.configure
 
       metric_exporter = OpenTelemetry::SDK::Metrics::Export::InMemoryMetricPullExporter.new
-      OpenTelemetry.meter_provider.add_metric_reader(metric_exporter)
+      metric_reader = OpenTelemetry::SDK::Metrics::Export::MetricReader.new(exporter: metric_exporter)
+      OpenTelemetry.meter_provider.add_metric_reader(metric_reader)
 
       meter = OpenTelemetry.meter_provider.meter('test')
       OpenTelemetry.meter_provider.add_view('retnuoc', aggregation: ::OpenTelemetry::SDK::Metrics::Aggregation::LastValue.new)
@@ -82,7 +85,7 @@
       counter.add(3)
       counter.add(4)
 
-      metric_exporter.pull
+      metric_reader.pull
       last_snapshot = metric_exporter.metric_snapshots
 
       _(last_snapshot[0].data_points).wont_be_empty