feat(configuration): add prometheus exporter support

experimental/CHANGELOG.md

@@ -15,6 +15,7 @@ For notes on migrating to 2.x / 0.200.x see [the upgrade guide](doc/upgrade-to-2
 
 ### :rocket: Features
 
+* feat(configuration): add Prometheus exporter support
 * feat(sampler-composite): add ComposableAnnotatingSampler and ComposableRuleBasedSampler [#6305](https://github.com/open-telemetry/opentelemetry-js/pull/6305) @trentm
 * feat(configuration): parse config for rc 3 [#6304](https://github.com/open-telemetry/opentelemetry-js/pull/6304) @maryliag
 * feat(instrumentation): use the `internals: true` option with import-in-the-middle hook, allowing instrumentations to hook internal files in ES modules [#6344](https://github.com/open-telemetry/opentelemetry-js/pull/6344) @trentm

experimental/packages/configuration/src/EnvironmentConfigFactory.ts

@@ -32,6 +32,7 @@ import {
   ExporterTemporalityPreference,
   initializeDefaultMeterProviderConfiguration,
   PeriodicMetricReader,
+  PullMetricReader,
 } from './models/meterProviderModel';
 import { OtlpHttpEncoding } from './models/commonModel';
 import { diag } from '@opentelemetry/api';
@@ -360,13 +361,29 @@ export function setMeterProvider(config: ConfigurationModel): void {
   }
   for (let i = 0; i < exportersType.length; i++) {
     const exporterType = exportersType[i];
+    if (exporterType === 'prometheus') {
+      // Prometheus uses a pull reader
+      const pullReader: PullMetricReader = {
+        exporter: {
+          'prometheus/development': {
+            host:
+              getStringFromEnv('OTEL_EXPORTER_PROMETHEUS_HOST') ?? 'localhost',
+            port: getNumberFromEnv('OTEL_EXPORTER_PROMETHEUS_PORT') ?? 9464,
+            without_scope_info: false,
+            without_target_info: false,
+          },
+        },
+      };
+      config.meter_provider.readers.push({ pull: pullReader });
+      continue;
+    }
+
     const readerPeriodicInfo = { ...readerPeriodic };
     const timeout = getNumberFromEnv('OTEL_METRIC_EXPORT_TIMEOUT') ?? 30000;
     if (timeout) {
       readerPeriodicInfo.timeout = timeout;
     }
 
-    // TODO: add prometheus exporter support
     if (exporterType === 'console') {
       readerPeriodicInfo.exporter = { console: {} };
     } else {

experimental/packages/configuration/test/ConfigFactory.test.ts

@@ -1414,6 +1414,64 @@ describe('ConfigFactory', function () {
       assert.deepStrictEqual(configFactory.getConfigModel(), expectedConfig);
     });
 
+    it('should return config with meter_provider with prometheus exporter', function () {
+      process.env.OTEL_METRICS_EXPORTER = 'prometheus';
+
+      const expectedConfig: ConfigurationModel = {
+        ...defaultConfig,
+        meter_provider: {
+          readers: [
+            {
+              pull: {
+                exporter: {
+                  'prometheus/development': {
+                    host: 'localhost',
+                    port: 9464,
+                    without_scope_info: false,
+                    without_target_info: false,
+                  },
+                },
+              },
+            },
+          ],
+          exemplar_filter: ExemplarFilter.TraceBased,
+          views: [],
+        },
+      };
+      const configFactory = createConfigFactory();
+      assert.deepStrictEqual(configFactory.getConfigModel(), expectedConfig);
+    });
+
+    it('should return config with meter_provider with prometheus exporter and custom port', function () {
+      process.env.OTEL_METRICS_EXPORTER = 'prometheus';
+      process.env.OTEL_EXPORTER_PROMETHEUS_HOST = '0.0.0.0';
+      process.env.OTEL_EXPORTER_PROMETHEUS_PORT = '8080';
+
+      const expectedConfig: ConfigurationModel = {
+        ...defaultConfig,
+        meter_provider: {
+          readers: [
+            {
+              pull: {
+                exporter: {
+                  'prometheus/development': {
+                    host: '0.0.0.0',
+                    port: 8080,
+                    without_scope_info: false,
+                    without_target_info: false,
+                  },
+                },
+              },
+            },
+          ],
+          exemplar_filter: ExemplarFilter.TraceBased,
+          views: [],
+        },
+      };
+      const configFactory = createConfigFactory();
+      assert.deepStrictEqual(configFactory.getConfigModel(), expectedConfig);
+    });
+
     it('should return config with meter_provider with no exporter', function () {
       process.env.OTEL_METRICS_EXPORTER = 'none,console';
       const configFactory = createConfigFactory();