feat: add prometheus exporter host and port env vars (#1857)

Author: Naseem

packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts

@@ -29,13 +29,15 @@ import { PrometheusLabelsBatcher } from './PrometheusLabelsBatcher';
 
 export class PrometheusExporter implements MetricExporter {
   static readonly DEFAULT_OPTIONS = {
+    host: undefined,
     port: 9464,
     endpoint: '/metrics',
     prefix: '',
     appendTimestamp: true,
   };
 
   private readonly _logger: api.Logger;
+  private readonly _host?: string;
   private readonly _port: number;
   private readonly _endpoint: string;
   private readonly _server: Server;
@@ -55,7 +57,14 @@ export class PrometheusExporter implements MetricExporter {
    */
   constructor(config: ExporterConfig = {}, callback?: () => void) {
     this._logger = config.logger || new api.NoopLogger();
-    this._port = config.port || PrometheusExporter.DEFAULT_OPTIONS.port;
+    this._host =
+      config.host ||
+      process.env.OTEL_EXPORTER_PROMETHEUS_HOST ||
+      PrometheusExporter.DEFAULT_OPTIONS.host;
+    this._port =
+      config.port ||
+      Number(process.env.OTEL_EXPORTER_PROMETHEUS_PORT) ||
+      PrometheusExporter.DEFAULT_OPTIONS.port;
     this._prefix = config.prefix || PrometheusExporter.DEFAULT_OPTIONS.prefix;
     this._appendTimestamp =
       typeof config.appendTimestamp === 'boolean'
@@ -72,7 +81,9 @@ export class PrometheusExporter implements MetricExporter {
     ).replace(/^([^/])/, '/$1');
 
     if (config.preventServerStart !== true) {
-      this.startServer().then(callback);
+      this.startServer()
+        .then(callback)
+        .catch(err => this._logger.error(err));
     } else if (callback) {
       callback();
     }
@@ -148,12 +159,18 @@ export class PrometheusExporter implements MetricExporter {
    */
   startServer(): Promise<void> {
     return new Promise(resolve => {
-      this._server.listen(this._port, () => {
-        this._logger.debug(
-          `Prometheus exporter started on port ${this._port} at endpoint ${this._endpoint}`
-        );
-        resolve();
-      });
+      this._server.listen(
+        {
+          port: this._port,
+          host: this._host,
+        },
+        () => {
+          this._logger.debug(
+            `Prometheus exporter server started: ${this._host}:${this._port}/${this._endpoint}`
+          );
+          resolve();
+        }
+      );
     });
   }
 

packages/opentelemetry-exporter-prometheus/src/export/types.ts

@@ -39,6 +39,11 @@ export interface ExporterConfig {
    */
   endpoint?: string;
 
+  /**
+   * @default undefined (all interfaces)
+   */
+  host?: string;
+
   /**
    * Port number for Prometheus exporter server
    *

packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts

@@ -35,6 +35,11 @@ describe('PrometheusExporter', () => {
   mockAggregator(LastValueAggregator);
   mockAggregator(HistogramAggregator);
 
+  afterEach(() => {
+    delete process.env.OTEL_EXPORTER_PROMETHEUS_HOST;
+    delete process.env.OTEL_EXPORTER_PROMETHEUS_PORT;
+  });
+
   describe('constructor', () => {
     it('should construct an exporter', done => {
       const exporter = new PrometheusExporter();
@@ -64,7 +69,7 @@ describe('PrometheusExporter', () => {
   });
 
   describe('server', () => {
-    it('it should start on startServer() and call the callback', done => {
+    it('should start on startServer() and call the callback', done => {
       const exporter = new PrometheusExporter({
         port: 9722,
         preventServerStart: true,
@@ -76,7 +81,7 @@ describe('PrometheusExporter', () => {
       });
     });
 
-    it('it should listen on the default port and default endpoint', done => {
+    it('should listen on the default port and default endpoint', done => {
       const port = PrometheusExporter.DEFAULT_OPTIONS.port;
       const endpoint = PrometheusExporter.DEFAULT_OPTIONS.endpoint;
       const exporter = new PrometheusExporter({}, () => {
@@ -90,7 +95,7 @@ describe('PrometheusExporter', () => {
       });
     });
 
-    it('it should listen on a custom port and endpoint if provided', done => {
+    it('should listen on a custom port and endpoint if provided', done => {
       const port = 9991;
       const endpoint = '/metric';
 
@@ -111,7 +116,17 @@ describe('PrometheusExporter', () => {
       );
     });
 
-    it('it should not require endpoints to start with a slash', done => {
+    it('should listen on environmentally set host and port', () => {
+      process.env.OTEL_EXPORTER_PROMETHEUS_HOST = '127.0.0.1';
+      process.env.OTEL_EXPORTER_PROMETHEUS_PORT = '1234';
+      const exporter = new PrometheusExporter({}, async () => {
+        await exporter.shutdown();
+      });
+      assert.strictEqual(exporter['_host'], '127.0.0.1');
+      assert.strictEqual(exporter['_port'], 1234);
+    });
+
+    it('should not require endpoints to start with a slash', done => {
       const port = 9991;
       const endpoint = 'metric';
 
@@ -146,7 +161,7 @@ describe('PrometheusExporter', () => {
       );
     });
 
-    it('it should return a HTTP status 404 if the endpoint does not match', done => {
+    it('should return a HTTP status 404 if the endpoint does not match', done => {
       const port = 9912;
       const endpoint = '/metrics';
       const exporter = new PrometheusExporter(