feat(prometheus): serialize resource as target_info gauge

experimental/CHANGELOG.md

@@ -9,6 +9,7 @@ All notable changes to experimental packages in this project will be documented
 ### :rocket: (Enhancement)
 
 * feat(sdk-node): configure trace exporter with environment variables [#3143](https://github.com/open-telemetry/opentelemetry-js/pull/3143) @svetlanabrennan
+* feat(prometheus): serialize resource as target_info gauge [#3300](https://github.com/open-telemetry/opentelemetry-js/pull/3300) @pichlermarc
 
 ### :bug: (Bug Fix)
 

experimental/examples/prometheus/package.json

@@ -1,6 +1,6 @@
 {
   "name": "prometheus-example",
-  "version": "0.32.0",
+  "version": "0.33.0",
   "description": "Example of using @opentelemetry/sdk-metrics and @opentelemetry/exporter-prometheus",
   "main": "index.js",
   "scripts": {
@@ -10,7 +10,7 @@
   "license": "Apache-2.0",
   "dependencies": {
     "@opentelemetry/api": "^1.0.2",
-    "@opentelemetry/exporter-prometheus": "0.32.0",
-    "@opentelemetry/sdk-metrics": "0.32.0"
+    "@opentelemetry/exporter-prometheus": "0.33.0",
+    "@opentelemetry/sdk-metrics": "0.33.0"
   }
 }

experimental/packages/opentelemetry-exporter-prometheus/package.json

@@ -61,7 +61,8 @@
   "dependencies": {
     "@opentelemetry/api-metrics": "0.33.0",
     "@opentelemetry/core": "1.7.0",
-    "@opentelemetry/sdk-metrics": "0.33.0"
+    "@opentelemetry/sdk-metrics": "0.33.0",
+    "@opentelemetry/resources": "1.7.0"
   },
   "homepage": "https://github.com/open-telemetry/opentelemetry-js/tree/main/experimental/packages/opentelemetry-exporter-prometheus"
 }

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

@@ -18,15 +18,22 @@ import { diag } from '@opentelemetry/api';
 import {
   globalErrorHandler,
 } from '@opentelemetry/core';
-import { Aggregation, AggregationTemporality, MetricReader } from '@opentelemetry/sdk-metrics';
-import { createServer, IncomingMessage, Server, ServerResponse } from 'http';
+import {
+  Aggregation,
+  AggregationTemporality,
+  MetricReader
+} from '@opentelemetry/sdk-metrics';
+import {
+  createServer,
+  IncomingMessage,
+  Server,
+  ServerResponse
+} from 'http';
 import { ExporterConfig } from './export/types';
 import { PrometheusSerializer } from './PrometheusSerializer';
 /** Node.js v8.x compat */
 import { URL } from 'url';
 
-const NO_REGISTERED_METRICS = '# no registered metrics';
-
 export class PrometheusExporter extends MetricReader {
   static readonly DEFAULT_OPTIONS = {
     host: undefined,
@@ -154,7 +161,7 @@ export class PrometheusExporter extends MetricReader {
 
   /**
    * Request handler that responds with the current state of metrics
-   * @param request Incoming HTTP request of server instance
+   * @param _request Incoming HTTP request of server instance
    * @param response HTTP response objet used to response to request
    */
   public getMetricsRequestHandler(
@@ -195,11 +202,7 @@ export class PrometheusExporter extends MetricReader {
           if (errors.length) {
             diag.error('PrometheusExporter: metrics collection errors', ...errors);
           }
-          let result = this._serializer.serialize(resourceMetrics);
-          if (result === '') {
-            result = NO_REGISTERED_METRICS;
-          }
-          response.end(result);
+          response.end(this._serializer.serialize(resourceMetrics));
         },
         err => {
           response.end(`# failed to export metrics: ${err}`);

experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts

@@ -29,6 +29,7 @@ import type {
   MetricAttributeValue
 } from '@opentelemetry/api-metrics';
 import { hrTimeToMilliseconds } from '@opentelemetry/core';
+import { Resource } from '@opentelemetry/resources';
 
 type PrometheusDataTypeLiteral =
   | 'counter'
@@ -167,6 +168,8 @@ function stringify(
   }\n`;
 }
 
+const NO_REGISTERED_METRICS = '# no registered metrics';
+
 export class PrometheusSerializer {
   private _prefix: string | undefined;
   private _appendTimestamp: boolean;
@@ -180,10 +183,16 @@ export class PrometheusSerializer {
 
   serialize(resourceMetrics: ResourceMetrics): string {
     let str = '';
+
     for (const scopeMetrics of resourceMetrics.scopeMetrics) {
       str += this._serializeScopeMetrics(scopeMetrics);
     }
-    return str;
+
+    if (str === '') {
+      str += NO_REGISTERED_METRICS;
+    }
+
+    return this._serializeResource(resourceMetrics.resource) + str;
   }
 
   private _serializeScopeMetrics(scopeMetrics: ScopeMetrics) {
@@ -311,4 +320,13 @@ export class PrometheusSerializer {
 
     return results;
   }
+
+  protected _serializeResource(resource: Resource): string {
+    const name = 'target_info';
+    const help = `# HELP ${name} Target metadata`;
+    const type = `# TYPE ${name} gauge`;
+
+    const results = stringify(name, resource.attributes, 1).trim();
+    return `${help}\n${type}\n${results}\n`;
+  }
 }

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

@@ -14,16 +14,28 @@
  * limitations under the License.
  */
 
-import { Meter, ObservableResult } from '@opentelemetry/api-metrics';
+import {
+  Meter,
+  ObservableResult
+} from '@opentelemetry/api-metrics';
 import { MeterProvider } from '@opentelemetry/sdk-metrics';
 import * as assert from 'assert';
 import * as sinon from 'sinon';
 import * as http from 'http';
 import { PrometheusExporter } from '../src';
-import { mockedHrTimeMs, mockHrTime } from './util';
+import {
+  mockedHrTimeMs,
+  mockHrTime
+} from './util';
 import { SinonStubbedInstance } from 'sinon';
 import { Counter } from '@opentelemetry/api-metrics';
 
+const serializedEmptyResourceLines = [
+  '# HELP target_info Target metadata',
+  '# TYPE target_info gauge',
+  'target_info 1'
+];
+
 describe('PrometheusExporter', () => {
   beforeEach(() => {
     mockHrTime();
@@ -249,11 +261,12 @@ describe('PrometheusExporter', () => {
       const lines = body.split('\n');
 
       assert.strictEqual(
-        lines[0],
+        lines[serializedEmptyResourceLines.length],
         '# HELP counter_total a test description'
       );
 
       assert.deepStrictEqual(lines, [
+        ...serializedEmptyResourceLines,
         '# HELP counter_total a test description',
         '# TYPE counter_total counter',
         `counter_total{key1="attributeValue1"} 10 ${mockedHrTimeMs}`,
@@ -283,6 +296,7 @@ describe('PrometheusExporter', () => {
       const lines = body.split('\n');
 
       assert.deepStrictEqual(lines, [
+        ...serializedEmptyResourceLines,
         '# HELP metric_observable_gauge a test description',
         '# TYPE metric_observable_gauge gauge',
         `metric_observable_gauge{pid="123",core="1"} 0.999 ${mockedHrTimeMs}`,
@@ -302,6 +316,7 @@ describe('PrometheusExporter', () => {
       const lines = body.split('\n');
 
       assert.deepStrictEqual(lines, [
+        ...serializedEmptyResourceLines,
         '# HELP counter_total a test description',
         '# TYPE counter_total counter',
         `counter_total{counterKey1="attributeValue1"} 10 ${mockedHrTimeMs}`,
@@ -331,11 +346,14 @@ describe('PrometheusExporter', () => {
       });
     });
 
-    it('should export a comment if no metrics are registered', async () => {
+    it('should export resource even if no metrics are registered', async () => {
       const body = await request('http://localhost:9464/metrics');
       const lines = body.split('\n');
 
-      assert.deepStrictEqual(lines, ['# no registered metrics']);
+      assert.deepStrictEqual(lines, [
+        ...serializedEmptyResourceLines,
+        '# no registered metrics'
+      ]);
     });
 
     it('should add a description if missing', async () => {
@@ -347,6 +365,7 @@ describe('PrometheusExporter', () => {
       const lines = body.split('\n');
 
       assert.deepStrictEqual(lines, [
+        ...serializedEmptyResourceLines,
         '# HELP counter_total description missing',
         '# TYPE counter_total counter',
         `counter_total{key1="attributeValue1"} 10 ${mockedHrTimeMs}`,
@@ -363,6 +382,7 @@ describe('PrometheusExporter', () => {
       const lines = body.split('\n');
 
       assert.deepStrictEqual(lines, [
+        ...serializedEmptyResourceLines,
         '# HELP counter_bad_name_total description missing',
         '# TYPE counter_bad_name_total counter',
         `counter_bad_name_total{key1="attributeValue1"} 10 ${mockedHrTimeMs}`,
@@ -380,14 +400,15 @@ describe('PrometheusExporter', () => {
       const body = await request('http://localhost:9464/metrics');
       const lines = body.split('\n');
       assert.deepStrictEqual(lines, [
+        ...serializedEmptyResourceLines,
         '# HELP counter a test description',
         '# TYPE counter gauge',
         `counter{key1="attributeValue1"} 20 ${mockedHrTimeMs}`,
         '',
       ]);
     });
 
-    it('should export an ObservableCounter as a counter', async() => {
+    it('should export an ObservableCounter as a counter', async () => {
       function getValue() {
         return 20;
       }
@@ -408,6 +429,7 @@ describe('PrometheusExporter', () => {
       const lines = body.split('\n');
 
       assert.deepStrictEqual(lines, [
+        ...serializedEmptyResourceLines,
         '# HELP metric_observable_counter a test description',
         '# TYPE metric_observable_counter counter',
         `metric_observable_counter{key1="attributeValue1"} 20 ${mockedHrTimeMs}`,
@@ -436,14 +458,15 @@ describe('PrometheusExporter', () => {
       const lines = body.split('\n');
 
       assert.deepStrictEqual(lines, [
+        ...serializedEmptyResourceLines,
         '# HELP metric_observable_up_down_counter a test description',
         '# TYPE metric_observable_up_down_counter gauge',
         `metric_observable_up_down_counter{key1="attributeValue1"} 20 ${mockedHrTimeMs}`,
         '',
       ]);
     });
 
-    it('should export a Histogram as a summary', async() => {
+    it('should export a Histogram as a summary', async () => {
       const histogram = meter.createHistogram('test_histogram', {
         description: 'a test description',
       });
@@ -454,6 +477,7 @@ describe('PrometheusExporter', () => {
       const lines = body.split('\n');
 
       assert.deepStrictEqual(lines, [
+        ...serializedEmptyResourceLines,
         '# HELP test_histogram a test description',
         '# TYPE test_histogram histogram',
         `test_histogram_count{key1="attributeValue1"} 1 ${mockedHrTimeMs}`,
@@ -507,6 +531,7 @@ describe('PrometheusExporter', () => {
                 const lines = body.split('\n');
 
                 assert.deepStrictEqual(lines, [
+                  ...serializedEmptyResourceLines,
                   '# HELP test_prefix_counter_total description missing',
                   '# TYPE test_prefix_counter_total counter',
                   `test_prefix_counter_total{key1="attributeValue1"} 10 ${mockedHrTimeMs}`,
@@ -535,6 +560,7 @@ describe('PrometheusExporter', () => {
                 const lines = body.split('\n');
 
                 assert.deepStrictEqual(lines, [
+                  ...serializedEmptyResourceLines,
                   '# HELP counter_total description missing',
                   '# TYPE counter_total counter',
                   `counter_total{key1="attributeValue1"} 10 ${mockedHrTimeMs}`,
@@ -563,6 +589,7 @@ describe('PrometheusExporter', () => {
                 const lines = body.split('\n');
 
                 assert.deepStrictEqual(lines, [
+                  ...serializedEmptyResourceLines,
                   '# HELP counter_total description missing',
                   '# TYPE counter_total counter',
                   `counter_total{key1="attributeValue1"} 10 ${mockedHrTimeMs}`,
@@ -591,6 +618,7 @@ describe('PrometheusExporter', () => {
                 const lines = body.split('\n');
 
                 assert.deepStrictEqual(lines, [
+                  ...serializedEmptyResourceLines,
                   '# HELP counter_total description missing',
                   '# TYPE counter_total counter',
                   'counter_total{key1="attributeValue1"} 10',