From 7c6281a1a786e237773556ce9dbb5ee9c979cab7 Mon Sep 17 00:00:00 2001
From: "marc.pichler" <marc.pichler@dynatrace.com>
Date: Thu, 6 Oct 2022 16:09:45 +0200
Subject: [PATCH 01/11] feat(prometheus): serialize resource as target_info
 gauge

---
 experimental/examples/prometheus/package.json |   7 +-
 .../examples/prometheus/prometheus.yml        |   1 +
 .../src/PrometheusExporter.ts                 |  15 +-
 .../src/PrometheusSerializer.ts               |  63 ++++-
 .../test/PrometheusExporter.test.ts           |  42 +++-
 .../test/PrometheusSerializer.test.ts         | 218 ++++++++++++++----
 .../tsconfig.json                             |   3 +
 lerna.json                                    |   1 +
 8 files changed, 294 insertions(+), 56 deletions(-)

diff --git a/experimental/examples/prometheus/package.json b/experimental/examples/prometheus/package.json
index 9816279e53..99f4a2a899 100644
--- a/experimental/examples/prometheus/package.json
+++ b/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 +10,8 @@
   "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",
+    "@opentelemetry/resources": "1.7.0"
   }
 }
diff --git a/experimental/examples/prometheus/prometheus.yml b/experimental/examples/prometheus/prometheus.yml
index 40ade8631d..c72c8593b8 100644
--- a/experimental/examples/prometheus/prometheus.yml
+++ b/experimental/examples/prometheus/prometheus.yml
@@ -5,5 +5,6 @@ scrape_configs:
   - job_name: 'opentelemetry'
     # metrics_path defaults to '/metrics'
     # scheme defaults to 'http'.
+    honor_labels: true
     static_configs:
     - targets: ['localhost:9464']
diff --git a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts
index 42b051e301..cbf20d0004 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts
@@ -18,8 +18,17 @@ 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 */
@@ -154,7 +163,7 @@ 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(
diff --git a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
index 94144732ac..8f3eab4873 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
@@ -24,11 +24,15 @@ import {
   DataPoint,
   Histogram,
 } from '@opentelemetry/sdk-metrics';
-import type {
+import { hrTimeToMilliseconds } from '@opentelemetry/core';
+import {
+  Resource,
+} from '@opentelemetry/resources';
+
+import {
   MetricAttributes,
   MetricAttributeValue
 } from '@opentelemetry/api-metrics';
-import { hrTimeToMilliseconds } from '@opentelemetry/core';
 
 type PrometheusDataTypeLiteral =
   | 'counter'
@@ -167,6 +171,43 @@ function stringify(
   }\n`;
 }
 
+export function filterReservedResourceAttributes(resource: Resource): MetricAttributes {
+  return Object.fromEntries(
+    Object.entries(resource.attributes)
+      .filter(([key]) => {
+        if (key === 'job') {
+          diag.warn('Cannot serialize reserved resource attribute "job".');
+          return true;
+        }
+        if (key === 'instance') {
+          diag.warn('Cannot serialize reserved resource attribute "instance".');
+          return true;
+        }
+
+        // drop any entries that will be used to construct 'job' and 'instance'
+        return key !== 'service.name' && key !== 'service.namespace' && key !== 'service.instance.id';
+      }
+      ));
+}
+
+function extractJobLabel(resource: Resource): string | undefined {
+  const serviceName = resource.attributes['service.name'];
+  const serviceNamespace = resource.attributes['service.namespace'];
+
+  if (serviceNamespace != null && serviceName != null) {
+    return `${serviceNamespace.toString()}/${serviceName.toString()}`;
+  } else if (serviceName != null) {
+    return serviceName.toString();
+  }
+
+  return undefined;
+}
+
+function extractInstanceLabel(resource: Resource): string | undefined {
+  const instance = resource.attributes['service.instance.id'];
+  return instance?.toString();
+}
+
 export class PrometheusSerializer {
   private _prefix: string | undefined;
   private _appendTimestamp: boolean;
@@ -179,7 +220,7 @@ export class PrometheusSerializer {
   }
 
   serialize(resourceMetrics: ResourceMetrics): string {
-    let str = '';
+    let str = this._serializeResource(resourceMetrics.resource);
     for (const scopeMetrics of resourceMetrics.scopeMetrics) {
       str += this._serializeScopeMetrics(scopeMetrics);
     }
@@ -311,4 +352,20 @@ export class PrometheusSerializer {
 
     return results;
   }
+
+  protected _serializeResource(resource: Resource): string {
+    const name = 'target_info';
+    const help = `# HELP ${name} Target metadata`;
+    const type = `# TYPE ${name} gauge`;
+
+    const resourceAttributes = filterReservedResourceAttributes(resource);
+
+    const otherAttributes = {
+      job: extractJobLabel(resource),
+      instance: extractInstanceLabel(resource)
+    };
+
+    const results = stringify(name, resourceAttributes, 1, undefined, otherAttributes).trim();
+    return `${help}\n${type}\n${results}\n`;
+  }
 }
diff --git a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts
index 080ac599e3..52dac40d54 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts
+++ b/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{job="",instance=""} 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,
+        ''
+      ]);
     });
 
     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}`,
@@ -380,6 +400,7 @@ 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}`,
@@ -387,7 +408,7 @@ describe('PrometheusExporter', () => {
       ]);
     });
 
-    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}`,
@@ -436,6 +458,7 @@ 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}`,
@@ -443,7 +466,7 @@ describe('PrometheusExporter', () => {
       ]);
     });
 
-    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',
diff --git a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts
index 1ae4ab8f53..69cc15c31d 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts
@@ -15,7 +15,10 @@
  */
 
 import * as assert from 'assert';
-import { MetricAttributes, UpDownCounter } from '@opentelemetry/api-metrics';
+import {
+  MetricAttributes,
+  UpDownCounter
+} from '@opentelemetry/api-metrics';
 import {
   Aggregation,
   AggregationTemporality,
@@ -31,13 +34,22 @@ import {
 } from '@opentelemetry/sdk-metrics';
 import * as sinon from 'sinon';
 import { PrometheusSerializer } from '../src';
-import { mockedHrTimeMs, mockHrTime } from './util';
+import {
+  mockedHrTimeMs,
+  mockHrTime
+} from './util';
+import { Resource } from '@opentelemetry/resources';
 
 const attributes = {
   foo1: 'bar1',
   foo2: 'bar2',
 };
 
+const serializedEmptyResource =
+  '# HELP target_info Target metadata\n' +
+  '# TYPE target_info gauge\n' +
+  'target_info{job="",instance=""} 1\n';
+
 class TestMetricReader extends MetricReader {
   constructor() {
     super({
@@ -147,11 +159,11 @@ describe('PrometheusSerializer', () => {
         assert.strictEqual(
           result,
           `test_count{foo1="bar1",foo2="bar2"} 1 ${mockedHrTimeMs}\n` +
-            `test_sum{foo1="bar1",foo2="bar2"} 5 ${mockedHrTimeMs}\n` +
-            `test_bucket{foo1="bar1",foo2="bar2",le="1"} 0 ${mockedHrTimeMs}\n` +
-            `test_bucket{foo1="bar1",foo2="bar2",le="10"} 1 ${mockedHrTimeMs}\n` +
-            `test_bucket{foo1="bar1",foo2="bar2",le="100"} 1 ${mockedHrTimeMs}\n` +
-            `test_bucket{foo1="bar1",foo2="bar2",le="+Inf"} 1 ${mockedHrTimeMs}\n`
+          `test_sum{foo1="bar1",foo2="bar2"} 5 ${mockedHrTimeMs}\n` +
+          `test_bucket{foo1="bar1",foo2="bar2",le="1"} 0 ${mockedHrTimeMs}\n` +
+          `test_bucket{foo1="bar1",foo2="bar2",le="10"} 1 ${mockedHrTimeMs}\n` +
+          `test_bucket{foo1="bar1",foo2="bar2",le="100"} 1 ${mockedHrTimeMs}\n` +
+          `test_bucket{foo1="bar1",foo2="bar2",le="+Inf"} 1 ${mockedHrTimeMs}\n`
         );
       });
 
@@ -161,11 +173,11 @@ describe('PrometheusSerializer', () => {
         assert.strictEqual(
           result,
           'test_count{foo1="bar1",foo2="bar2"} 1\n' +
-            'test_sum{foo1="bar1",foo2="bar2"} 5\n' +
-            'test_bucket{foo1="bar1",foo2="bar2",le="1"} 0\n' +
-            'test_bucket{foo1="bar1",foo2="bar2",le="10"} 1\n' +
-            'test_bucket{foo1="bar1",foo2="bar2",le="100"} 1\n' +
-            'test_bucket{foo1="bar1",foo2="bar2",le="+Inf"} 1\n'
+          'test_sum{foo1="bar1",foo2="bar2"} 5\n' +
+          'test_bucket{foo1="bar1",foo2="bar2",le="1"} 0\n' +
+          'test_bucket{foo1="bar1",foo2="bar2",le="10"} 1\n' +
+          'test_bucket{foo1="bar1",foo2="bar2",le="100"} 1\n' +
+          'test_bucket{foo1="bar1",foo2="bar2",le="+Inf"} 1\n'
         );
       });
     });
@@ -203,9 +215,9 @@ describe('PrometheusSerializer', () => {
         assert.strictEqual(
           result,
           '# HELP test_total foobar\n' +
-            '# TYPE test_total counter\n' +
-            `test_total{val="1"} 1 ${mockedHrTimeMs}\n` +
-            `test_total{val="2"} 1 ${mockedHrTimeMs}\n`
+          '# TYPE test_total counter\n' +
+          `test_total{val="1"} 1 ${mockedHrTimeMs}\n` +
+          `test_total{val="2"} 1 ${mockedHrTimeMs}\n`
         );
       });
 
@@ -215,9 +227,9 @@ describe('PrometheusSerializer', () => {
         assert.strictEqual(
           result,
           '# HELP test_total foobar\n' +
-            '# TYPE test_total counter\n' +
-            'test_total{val="1"} 1\n' +
-            'test_total{val="2"} 1\n'
+          '# TYPE test_total counter\n' +
+          'test_total{val="1"} 1\n' +
+          'test_total{val="2"} 1\n'
         );
       });
     });
@@ -278,7 +290,7 @@ describe('PrometheusSerializer', () => {
         const reader = new TestMetricReader();
         const meterProvider = new MeterProvider({
           views: [
-            new View({aggregation: new LastValueAggregation(), instrumentName: '*' })
+            new View({ aggregation: new LastValueAggregation(), instrumentName: '*' })
           ]
         });
         meterProvider.addMetricReader(reader);
@@ -361,19 +373,19 @@ describe('PrometheusSerializer', () => {
         assert.strictEqual(
           result,
           '# HELP test foobar\n' +
-            '# TYPE test histogram\n' +
-            `test_count{val="1"} 3 ${mockedHrTimeMs}\n` +
-            `test_sum{val="1"} 175 ${mockedHrTimeMs}\n` +
-            `test_bucket{val="1",le="1"} 0 ${mockedHrTimeMs}\n` +
-            `test_bucket{val="1",le="10"} 1 ${mockedHrTimeMs}\n` +
-            `test_bucket{val="1",le="100"} 2 ${mockedHrTimeMs}\n` +
-            `test_bucket{val="1",le="+Inf"} 3 ${mockedHrTimeMs}\n` +
-            `test_count{val="2"} 1 ${mockedHrTimeMs}\n` +
-            `test_sum{val="2"} 5 ${mockedHrTimeMs}\n` +
-            `test_bucket{val="2",le="1"} 0 ${mockedHrTimeMs}\n` +
-            `test_bucket{val="2",le="10"} 1 ${mockedHrTimeMs}\n` +
-            `test_bucket{val="2",le="100"} 1 ${mockedHrTimeMs}\n` +
-            `test_bucket{val="2",le="+Inf"} 1 ${mockedHrTimeMs}\n`
+          '# TYPE test histogram\n' +
+          `test_count{val="1"} 3 ${mockedHrTimeMs}\n` +
+          `test_sum{val="1"} 175 ${mockedHrTimeMs}\n` +
+          `test_bucket{val="1",le="1"} 0 ${mockedHrTimeMs}\n` +
+          `test_bucket{val="1",le="10"} 1 ${mockedHrTimeMs}\n` +
+          `test_bucket{val="1",le="100"} 2 ${mockedHrTimeMs}\n` +
+          `test_bucket{val="1",le="+Inf"} 3 ${mockedHrTimeMs}\n` +
+          `test_count{val="2"} 1 ${mockedHrTimeMs}\n` +
+          `test_sum{val="2"} 5 ${mockedHrTimeMs}\n` +
+          `test_bucket{val="2",le="1"} 0 ${mockedHrTimeMs}\n` +
+          `test_bucket{val="2",le="10"} 1 ${mockedHrTimeMs}\n` +
+          `test_bucket{val="2",le="100"} 1 ${mockedHrTimeMs}\n` +
+          `test_bucket{val="2",le="+Inf"} 1 ${mockedHrTimeMs}\n`
         );
       });
 
@@ -465,6 +477,7 @@ describe('PrometheusSerializer', () => {
       const result = await getCounterResult('test', serializer, { unit: unitOfMetric, exportAll: true });
       assert.strictEqual(
         result,
+        serializedEmptyResource +
         '# HELP test_total description missing\n' +
         `# UNIT test_total ${unitOfMetric}\n` +
         '# TYPE test_total counter\n' +
@@ -478,6 +491,7 @@ describe('PrometheusSerializer', () => {
       const result = await getCounterResult('test', serializer, { exportAll: true });
       assert.strictEqual(
         result,
+        serializedEmptyResource +
         '# HELP test_total description missing\n' +
         '# TYPE test_total counter\n' +
         `test_total 1 ${mockedHrTimeMs}\n`
@@ -593,13 +607,13 @@ describe('PrometheusSerializer', () => {
       assert.strictEqual(
         result,
         'test_total{' +
-          'backslash="\u005c\u005c",' +
-          'doubleQuote="\u005c\u0022",' +
-          'lineFeed="\u005c\u006e",' +
-          'backslashN="\u005c\u005c\u006e",' +
-          'backslashDoubleQuote="\u005c\u005c\u005c\u0022",' +
-          'backslashLineFeed="\u005c\u005c\u005c\u006e"' +
-          `} 1 ${mockedHrTimeMs}\n`
+        'backslash="\u005c\u005c",' +
+        'doubleQuote="\u005c\u0022",' +
+        'lineFeed="\u005c\u006e",' +
+        'backslashN="\u005c\u005c\u006e",' +
+        'backslashDoubleQuote="\u005c\u005c\u005c\u0022",' +
+        'backslashLineFeed="\u005c\u005c\u005c\u006e"' +
+        `} 1 ${mockedHrTimeMs}\n`
       );
     });
 
@@ -607,7 +621,7 @@ describe('PrometheusSerializer', () => {
       const serializer = new PrometheusSerializer();
 
       const result = await testSerializer(serializer, 'test_total', counter => {
-        // if you try to use a attribute name like account-id prometheus will complain
+        // if you try to use an attribute name like account-id prometheus will complain
         // with an error like:
         // error while linting: text format parsing error in line 282: expected '=' after label name, found '-'
         counter.add(1, ({
@@ -621,4 +635,128 @@ describe('PrometheusSerializer', () => {
       );
     });
   });
+
+  describe('_serializeResource', () => {
+    it('should serialize resource', () => {
+      const serializer = new PrometheusSerializer(undefined, true);
+      const result = serializer['_serializeResource'](new Resource({
+        env: 'prod',
+        hostname: 'myhost',
+        datacenter: 'sdc',
+        region: 'europe',
+        owner: 'frontend'
+      }));
+
+      assert.strictEqual(
+        result,
+        '# HELP target_info Target metadata\n' +
+        '# TYPE target_info gauge\n' +
+        'target_info{env="prod",hostname="myhost",datacenter="sdc",region="europe",owner="frontend",job="",instance=""} 1\n'
+      );
+    });
+
+    it('should drop service attributes', () => {
+      const serializer = new PrometheusSerializer(undefined, true);
+      const result = serializer['_serializeResource'](new Resource({
+        env: 'prod',
+        hostname: 'myhost',
+        datacenter: 'sdc',
+        region: 'europe',
+        owner: 'frontend',
+        'service.name': 'name',
+        'service.namespace': 'namespace',
+        'service.instance.id': 'instance id'
+      }));
+
+      assert.strictEqual(
+        result,
+        '# HELP target_info Target metadata\n' +
+        '# TYPE target_info gauge\n' +
+        'target_info{env="prod",hostname="myhost",datacenter="sdc",region="europe",owner="frontend",job="namespace/name",instance="instance id"} 1\n'
+      );
+    });
+
+    it('with undefined service.instance.id should add empty instance id', () => {
+      const serializer = new PrometheusSerializer(undefined, true);
+      const result = serializer['_serializeResource'](new Resource({
+        foo: 'bar',
+        'service.name': 'name',
+        'service.namespace': 'namespace',
+      }));
+
+      assert.strictEqual(
+        result,
+        '# HELP target_info Target metadata\n' +
+        '# TYPE target_info gauge\n' +
+        'target_info{foo="bar",job="namespace/name",instance=""} 1\n'
+      );
+    });
+
+    it('with undefined service.instance.id should add empty instance id', () => {
+      const serializer = new PrometheusSerializer(undefined, true);
+      const result = serializer['_serializeResource'](new Resource({
+        foo: 'bar',
+        'service.name': 'name',
+        'service.namespace': 'namespace',
+      }));
+
+      assert.strictEqual(
+        result,
+        '# HELP target_info Target metadata\n' +
+        '# TYPE target_info gauge\n' +
+        'target_info{foo="bar",job="namespace/name",instance=""} 1\n'
+      );
+    });
+
+    it('with undefined service.namespace should only use service.name for "job"', () => {
+      const serializer = new PrometheusSerializer(undefined, true);
+      const result = serializer['_serializeResource'](new Resource({
+        foo: 'bar',
+        'service.name': 'name',
+        'service.instance.id': '123'
+      }));
+
+      assert.strictEqual(
+        result,
+        '# HELP target_info Target metadata\n' +
+        '# TYPE target_info gauge\n' +
+        'target_info{foo="bar",job="name",instance="123"} 1\n'
+      );
+    });
+
+    it('with undefined service.namespace and service.name should add empty "job"', () => {
+      // service.name MUST exist. But PrometheusSerializer is exported and used by non-SDK packages.
+      // In case semantic conventions are not adhered to, add empty as a fallback.
+      const serializer = new PrometheusSerializer(undefined, true);
+      const result = serializer['_serializeResource'](new Resource({
+        foo: 'bar',
+        'service.instance.id': '123'
+      }));
+
+      assert.strictEqual(
+        result,
+        '# HELP target_info Target metadata\n' +
+        '# TYPE target_info gauge\n' +
+        'target_info{foo="bar",job="",instance="123"} 1\n'
+      );
+    });
+
+    it('with defined service.namespace and undefined service.name should add empty "job"', () => {
+      // service.name MUST exist. But PrometheusSerializer is exported and used by non-SDK packages.
+      // In case semantic conventions are not adhered to, add empty as a fallback.
+      const serializer = new PrometheusSerializer(undefined, true);
+      const result = serializer['_serializeResource'](new Resource({
+        foo: 'bar',
+        'service.instance.id': '123',
+        'service.namespace': 'namespace'
+      }));
+
+      assert.strictEqual(
+        result,
+        '# HELP target_info Target metadata\n' +
+        '# TYPE target_info gauge\n' +
+        'target_info{foo="bar",job="",instance="123"} 1\n'
+      );
+    });
+  });
 });
diff --git a/experimental/packages/opentelemetry-exporter-prometheus/tsconfig.json b/experimental/packages/opentelemetry-exporter-prometheus/tsconfig.json
index 138ffc3aad..1283f8e6d4 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/tsconfig.json
+++ b/experimental/packages/opentelemetry-exporter-prometheus/tsconfig.json
@@ -15,6 +15,9 @@
     {
       "path": "../../../packages/opentelemetry-core"
     },
+    {
+      "path": "../../../packages/opentelemetry-resources"
+    },
     {
       "path": "../opentelemetry-api-metrics"
     },
diff --git a/lerna.json b/lerna.json
index 5c0f76b9c2..d97ab02a62 100644
--- a/lerna.json
+++ b/lerna.json
@@ -5,6 +5,7 @@
     "api",
     "packages/*",
     "experimental/packages/*",
+    "experimental/examples/*",
     "experimental/backwards-compatability/*",
     "integration-tests/*",
     "selenium-tests",

From ccc189930f4170bdacebbeaea69ff70c7bb3bc9f Mon Sep 17 00:00:00 2001
From: "marc.pichler" <marc.pichler@dynatrace.com>
Date: Fri, 7 Oct 2022 09:00:20 +0200
Subject: [PATCH 02/11] feat(prometheus): do not export
 filterReservedResourceAttributes

---
 .../src/PrometheusSerializer.ts                                 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
index 8f3eab4873..c7949a5d85 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
@@ -171,7 +171,7 @@ function stringify(
   }\n`;
 }
 
-export function filterReservedResourceAttributes(resource: Resource): MetricAttributes {
+function filterReservedResourceAttributes(resource: Resource): MetricAttributes {
   return Object.fromEntries(
     Object.entries(resource.attributes)
       .filter(([key]) => {

From 32791dfc727724d997a4fb4cd55b2481f847bee1 Mon Sep 17 00:00:00 2001
From: "marc.pichler" <marc.pichler@dynatrace.com>
Date: Fri, 7 Oct 2022 09:57:35 +0200
Subject: [PATCH 03/11] fix(changelog): add changelog entry

---
 experimental/CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/experimental/CHANGELOG.md b/experimental/CHANGELOG.md
index f14d274c65..3c785831fd 100644
--- a/experimental/CHANGELOG.md
+++ b/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)
 

From 2c839081a8047da2b4f76aa5fe5d6c2a848abe85 Mon Sep 17 00:00:00 2001
From: "marc.pichler" <marc.pichler@dynatrace.com>
Date: Fri, 7 Oct 2022 10:06:50 +0200
Subject: [PATCH 04/11] feat(prometheus): add resources dependency

---
 .../packages/opentelemetry-exporter-prometheus/package.json    | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/experimental/packages/opentelemetry-exporter-prometheus/package.json b/experimental/packages/opentelemetry-exporter-prometheus/package.json
index 0067320ed4..62243f78c4 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/package.json
+++ b/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"
 }

From 3993d860c0a0f064dd603862fbddfd5df0e83c16 Mon Sep 17 00:00:00 2001
From: "marc.pichler" <marc.pichler@dynatrace.com>
Date: Mon, 10 Oct 2022 13:49:39 +0200
Subject: [PATCH 05/11] fix(prometheus-example): remove resources package.

---
 .../packages/opentelemetry-exporter-prometheus/package.json    | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/experimental/packages/opentelemetry-exporter-prometheus/package.json b/experimental/packages/opentelemetry-exporter-prometheus/package.json
index 62243f78c4..0067320ed4 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/package.json
+++ b/experimental/packages/opentelemetry-exporter-prometheus/package.json
@@ -61,8 +61,7 @@
   "dependencies": {
     "@opentelemetry/api-metrics": "0.33.0",
     "@opentelemetry/core": "1.7.0",
-    "@opentelemetry/sdk-metrics": "0.33.0",
-    "@opentelemetry/resources": "1.7.0"
+    "@opentelemetry/sdk-metrics": "0.33.0"
   },
   "homepage": "https://github.com/open-telemetry/opentelemetry-js/tree/main/experimental/packages/opentelemetry-exporter-prometheus"
 }

From 7e338e6067c8f1a3d6677fd885fc1a387a59b282 Mon Sep 17 00:00:00 2001
From: "marc.pichler" <marc.pichler@dynatrace.com>
Date: Mon, 10 Oct 2022 15:56:53 +0200
Subject: [PATCH 06/11] fix(prometheus-exporter): remove generation of job and
 instance labels

---
 .../src/PrometheusSerializer.ts               |  46 +-------
 .../test/PrometheusExporter.test.ts           |   2 +-
 .../test/PrometheusSerializer.test.ts         | 108 +-----------------
 3 files changed, 4 insertions(+), 152 deletions(-)

diff --git a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
index c7949a5d85..124d59327c 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
@@ -171,43 +171,6 @@ function stringify(
   }\n`;
 }
 
-function filterReservedResourceAttributes(resource: Resource): MetricAttributes {
-  return Object.fromEntries(
-    Object.entries(resource.attributes)
-      .filter(([key]) => {
-        if (key === 'job') {
-          diag.warn('Cannot serialize reserved resource attribute "job".');
-          return true;
-        }
-        if (key === 'instance') {
-          diag.warn('Cannot serialize reserved resource attribute "instance".');
-          return true;
-        }
-
-        // drop any entries that will be used to construct 'job' and 'instance'
-        return key !== 'service.name' && key !== 'service.namespace' && key !== 'service.instance.id';
-      }
-      ));
-}
-
-function extractJobLabel(resource: Resource): string | undefined {
-  const serviceName = resource.attributes['service.name'];
-  const serviceNamespace = resource.attributes['service.namespace'];
-
-  if (serviceNamespace != null && serviceName != null) {
-    return `${serviceNamespace.toString()}/${serviceName.toString()}`;
-  } else if (serviceName != null) {
-    return serviceName.toString();
-  }
-
-  return undefined;
-}
-
-function extractInstanceLabel(resource: Resource): string | undefined {
-  const instance = resource.attributes['service.instance.id'];
-  return instance?.toString();
-}
-
 export class PrometheusSerializer {
   private _prefix: string | undefined;
   private _appendTimestamp: boolean;
@@ -358,14 +321,7 @@ export class PrometheusSerializer {
     const help = `# HELP ${name} Target metadata`;
     const type = `# TYPE ${name} gauge`;
 
-    const resourceAttributes = filterReservedResourceAttributes(resource);
-
-    const otherAttributes = {
-      job: extractJobLabel(resource),
-      instance: extractInstanceLabel(resource)
-    };
-
-    const results = stringify(name, resourceAttributes, 1, undefined, otherAttributes).trim();
+    const results = stringify(name, resource.attributes, 1).trim();
     return `${help}\n${type}\n${results}\n`;
   }
 }
diff --git a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts
index 52dac40d54..20a8d5b9ce 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts
@@ -33,7 +33,7 @@ import { Counter } from '@opentelemetry/api-metrics';
 const serializedEmptyResourceLines = [
   '# HELP target_info Target metadata',
   '# TYPE target_info gauge',
-  'target_info{job="",instance=""} 1'
+  'target_info 1'
 ];
 
 describe('PrometheusExporter', () => {
diff --git a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts
index 69cc15c31d..759ea85f0f 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts
@@ -48,7 +48,7 @@ const attributes = {
 const serializedEmptyResource =
   '# HELP target_info Target metadata\n' +
   '# TYPE target_info gauge\n' +
-  'target_info{job="",instance=""} 1\n';
+  'target_info 1\n';
 
 class TestMetricReader extends MetricReader {
   constructor() {
@@ -651,111 +651,7 @@ describe('PrometheusSerializer', () => {
         result,
         '# HELP target_info Target metadata\n' +
         '# TYPE target_info gauge\n' +
-        'target_info{env="prod",hostname="myhost",datacenter="sdc",region="europe",owner="frontend",job="",instance=""} 1\n'
-      );
-    });
-
-    it('should drop service attributes', () => {
-      const serializer = new PrometheusSerializer(undefined, true);
-      const result = serializer['_serializeResource'](new Resource({
-        env: 'prod',
-        hostname: 'myhost',
-        datacenter: 'sdc',
-        region: 'europe',
-        owner: 'frontend',
-        'service.name': 'name',
-        'service.namespace': 'namespace',
-        'service.instance.id': 'instance id'
-      }));
-
-      assert.strictEqual(
-        result,
-        '# HELP target_info Target metadata\n' +
-        '# TYPE target_info gauge\n' +
-        'target_info{env="prod",hostname="myhost",datacenter="sdc",region="europe",owner="frontend",job="namespace/name",instance="instance id"} 1\n'
-      );
-    });
-
-    it('with undefined service.instance.id should add empty instance id', () => {
-      const serializer = new PrometheusSerializer(undefined, true);
-      const result = serializer['_serializeResource'](new Resource({
-        foo: 'bar',
-        'service.name': 'name',
-        'service.namespace': 'namespace',
-      }));
-
-      assert.strictEqual(
-        result,
-        '# HELP target_info Target metadata\n' +
-        '# TYPE target_info gauge\n' +
-        'target_info{foo="bar",job="namespace/name",instance=""} 1\n'
-      );
-    });
-
-    it('with undefined service.instance.id should add empty instance id', () => {
-      const serializer = new PrometheusSerializer(undefined, true);
-      const result = serializer['_serializeResource'](new Resource({
-        foo: 'bar',
-        'service.name': 'name',
-        'service.namespace': 'namespace',
-      }));
-
-      assert.strictEqual(
-        result,
-        '# HELP target_info Target metadata\n' +
-        '# TYPE target_info gauge\n' +
-        'target_info{foo="bar",job="namespace/name",instance=""} 1\n'
-      );
-    });
-
-    it('with undefined service.namespace should only use service.name for "job"', () => {
-      const serializer = new PrometheusSerializer(undefined, true);
-      const result = serializer['_serializeResource'](new Resource({
-        foo: 'bar',
-        'service.name': 'name',
-        'service.instance.id': '123'
-      }));
-
-      assert.strictEqual(
-        result,
-        '# HELP target_info Target metadata\n' +
-        '# TYPE target_info gauge\n' +
-        'target_info{foo="bar",job="name",instance="123"} 1\n'
-      );
-    });
-
-    it('with undefined service.namespace and service.name should add empty "job"', () => {
-      // service.name MUST exist. But PrometheusSerializer is exported and used by non-SDK packages.
-      // In case semantic conventions are not adhered to, add empty as a fallback.
-      const serializer = new PrometheusSerializer(undefined, true);
-      const result = serializer['_serializeResource'](new Resource({
-        foo: 'bar',
-        'service.instance.id': '123'
-      }));
-
-      assert.strictEqual(
-        result,
-        '# HELP target_info Target metadata\n' +
-        '# TYPE target_info gauge\n' +
-        'target_info{foo="bar",job="",instance="123"} 1\n'
-      );
-    });
-
-    it('with defined service.namespace and undefined service.name should add empty "job"', () => {
-      // service.name MUST exist. But PrometheusSerializer is exported and used by non-SDK packages.
-      // In case semantic conventions are not adhered to, add empty as a fallback.
-      const serializer = new PrometheusSerializer(undefined, true);
-      const result = serializer['_serializeResource'](new Resource({
-        foo: 'bar',
-        'service.instance.id': '123',
-        'service.namespace': 'namespace'
-      }));
-
-      assert.strictEqual(
-        result,
-        '# HELP target_info Target metadata\n' +
-        '# TYPE target_info gauge\n' +
-        'target_info{foo="bar",job="",instance="123"} 1\n'
+        'target_info{env="prod",hostname="myhost",datacenter="sdc",region="europe",owner="frontend"} 1\n'
       );
     });
   });

From 993199c358f7dd578eb00b2ce6bc7f25f6db63cd Mon Sep 17 00:00:00 2001
From: "marc.pichler" <marc.pichler@dynatrace.com>
Date: Mon, 10 Oct 2022 16:04:04 +0200
Subject: [PATCH 07/11] fix(prometheus-example): remove resources package.

---
 experimental/examples/prometheus/package.json                  | 3 +--
 .../packages/opentelemetry-exporter-prometheus/package.json    | 3 ++-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/experimental/examples/prometheus/package.json b/experimental/examples/prometheus/package.json
index 99f4a2a899..837fcf9b61 100644
--- a/experimental/examples/prometheus/package.json
+++ b/experimental/examples/prometheus/package.json
@@ -11,7 +11,6 @@
   "dependencies": {
     "@opentelemetry/api": "^1.0.2",
     "@opentelemetry/exporter-prometheus": "0.33.0",
-    "@opentelemetry/sdk-metrics": "0.33.0",
-    "@opentelemetry/resources": "1.7.0"
+    "@opentelemetry/sdk-metrics": "0.33.0"
   }
 }
diff --git a/experimental/packages/opentelemetry-exporter-prometheus/package.json b/experimental/packages/opentelemetry-exporter-prometheus/package.json
index e45cdd33c6..c8305d3c88 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/package.json
+++ b/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"
 }

From dfd8a9f78bb0b51211d843d9990717bd0b612319 Mon Sep 17 00:00:00 2001
From: "marc.pichler" <marc.pichler@dynatrace.com>
Date: Mon, 10 Oct 2022 16:05:07 +0200
Subject: [PATCH 08/11] fix(prometheus-example): remove 'honor_lables' setting

---
 experimental/examples/prometheus/prometheus.yml | 1 -
 1 file changed, 1 deletion(-)

diff --git a/experimental/examples/prometheus/prometheus.yml b/experimental/examples/prometheus/prometheus.yml
index c72c8593b8..40ade8631d 100644
--- a/experimental/examples/prometheus/prometheus.yml
+++ b/experimental/examples/prometheus/prometheus.yml
@@ -5,6 +5,5 @@ scrape_configs:
   - job_name: 'opentelemetry'
     # metrics_path defaults to '/metrics'
     # scheme defaults to 'http'.
-    honor_labels: true
     static_configs:
     - targets: ['localhost:9464']

From e22b2d3ad1c56c9df7dcc21223f67f955e322fe6 Mon Sep 17 00:00:00 2001
From: "marc.pichler" <marc.pichler@dynatrace.com>
Date: Mon, 10 Oct 2022 16:43:01 +0200
Subject: [PATCH 09/11] fix(exporter-prometheus): undo auto-formatting

---
 .../src/PrometheusSerializer.ts               |  9 +--
 .../test/PrometheusSerializer.test.ts         | 70 +++++++++----------
 2 files changed, 38 insertions(+), 41 deletions(-)

diff --git a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
index 124d59327c..065244a089 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
@@ -24,15 +24,12 @@ import {
   DataPoint,
   Histogram,
 } from '@opentelemetry/sdk-metrics';
-import { hrTimeToMilliseconds } from '@opentelemetry/core';
-import {
-  Resource,
-} from '@opentelemetry/resources';
-
-import {
+import type {
   MetricAttributes,
   MetricAttributeValue
 } from '@opentelemetry/api-metrics';
+import { hrTimeToMilliseconds } from '@opentelemetry/core';
+import { Resource } from '@opentelemetry/resources';
 
 type PrometheusDataTypeLiteral =
   | 'counter'
diff --git a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts
index 759ea85f0f..627ddc7a9f 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts
@@ -159,11 +159,11 @@ describe('PrometheusSerializer', () => {
         assert.strictEqual(
           result,
           `test_count{foo1="bar1",foo2="bar2"} 1 ${mockedHrTimeMs}\n` +
-          `test_sum{foo1="bar1",foo2="bar2"} 5 ${mockedHrTimeMs}\n` +
-          `test_bucket{foo1="bar1",foo2="bar2",le="1"} 0 ${mockedHrTimeMs}\n` +
-          `test_bucket{foo1="bar1",foo2="bar2",le="10"} 1 ${mockedHrTimeMs}\n` +
-          `test_bucket{foo1="bar1",foo2="bar2",le="100"} 1 ${mockedHrTimeMs}\n` +
-          `test_bucket{foo1="bar1",foo2="bar2",le="+Inf"} 1 ${mockedHrTimeMs}\n`
+            `test_sum{foo1="bar1",foo2="bar2"} 5 ${mockedHrTimeMs}\n` +
+            `test_bucket{foo1="bar1",foo2="bar2",le="1"} 0 ${mockedHrTimeMs}\n` +
+            `test_bucket{foo1="bar1",foo2="bar2",le="10"} 1 ${mockedHrTimeMs}\n` +
+            `test_bucket{foo1="bar1",foo2="bar2",le="100"} 1 ${mockedHrTimeMs}\n` +
+            `test_bucket{foo1="bar1",foo2="bar2",le="+Inf"} 1 ${mockedHrTimeMs}\n`
         );
       });
 
@@ -173,11 +173,11 @@ describe('PrometheusSerializer', () => {
         assert.strictEqual(
           result,
           'test_count{foo1="bar1",foo2="bar2"} 1\n' +
-          'test_sum{foo1="bar1",foo2="bar2"} 5\n' +
-          'test_bucket{foo1="bar1",foo2="bar2",le="1"} 0\n' +
-          'test_bucket{foo1="bar1",foo2="bar2",le="10"} 1\n' +
-          'test_bucket{foo1="bar1",foo2="bar2",le="100"} 1\n' +
-          'test_bucket{foo1="bar1",foo2="bar2",le="+Inf"} 1\n'
+            'test_sum{foo1="bar1",foo2="bar2"} 5\n' +
+            'test_bucket{foo1="bar1",foo2="bar2",le="1"} 0\n' +
+            'test_bucket{foo1="bar1",foo2="bar2",le="10"} 1\n' +
+            'test_bucket{foo1="bar1",foo2="bar2",le="100"} 1\n' +
+            'test_bucket{foo1="bar1",foo2="bar2",le="+Inf"} 1\n'
         );
       });
     });
@@ -266,9 +266,9 @@ describe('PrometheusSerializer', () => {
         assert.strictEqual(
           result,
           '# HELP test_total foobar\n' +
-          '# TYPE test_total gauge\n' +
-          `test_total{val="1"} 1 ${mockedHrTimeMs}\n` +
-          `test_total{val="2"} 1 ${mockedHrTimeMs}\n`
+            '# TYPE test_total gauge\n' +
+            `test_total{val="1"} 1 ${mockedHrTimeMs}\n` +
+            `test_total{val="2"} 1 ${mockedHrTimeMs}\n`
         );
       });
 
@@ -278,9 +278,9 @@ describe('PrometheusSerializer', () => {
         assert.strictEqual(
           result,
           '# HELP test_total foobar\n' +
-          '# TYPE test_total gauge\n' +
-          'test_total{val="1"} 1\n' +
-          'test_total{val="2"} 1\n'
+            '# TYPE test_total gauge\n' +
+            'test_total{val="1"} 1\n' +
+            'test_total{val="2"} 1\n'
         );
       });
     });
@@ -374,18 +374,18 @@ describe('PrometheusSerializer', () => {
           result,
           '# HELP test foobar\n' +
           '# TYPE test histogram\n' +
-          `test_count{val="1"} 3 ${mockedHrTimeMs}\n` +
-          `test_sum{val="1"} 175 ${mockedHrTimeMs}\n` +
-          `test_bucket{val="1",le="1"} 0 ${mockedHrTimeMs}\n` +
-          `test_bucket{val="1",le="10"} 1 ${mockedHrTimeMs}\n` +
-          `test_bucket{val="1",le="100"} 2 ${mockedHrTimeMs}\n` +
-          `test_bucket{val="1",le="+Inf"} 3 ${mockedHrTimeMs}\n` +
-          `test_count{val="2"} 1 ${mockedHrTimeMs}\n` +
-          `test_sum{val="2"} 5 ${mockedHrTimeMs}\n` +
-          `test_bucket{val="2",le="1"} 0 ${mockedHrTimeMs}\n` +
-          `test_bucket{val="2",le="10"} 1 ${mockedHrTimeMs}\n` +
-          `test_bucket{val="2",le="100"} 1 ${mockedHrTimeMs}\n` +
-          `test_bucket{val="2",le="+Inf"} 1 ${mockedHrTimeMs}\n`
+            `test_count{val="1"} 3 ${mockedHrTimeMs}\n` +
+            `test_sum{val="1"} 175 ${mockedHrTimeMs}\n` +
+            `test_bucket{val="1",le="1"} 0 ${mockedHrTimeMs}\n` +
+            `test_bucket{val="1",le="10"} 1 ${mockedHrTimeMs}\n` +
+            `test_bucket{val="1",le="100"} 2 ${mockedHrTimeMs}\n` +
+            `test_bucket{val="1",le="+Inf"} 3 ${mockedHrTimeMs}\n` +
+            `test_count{val="2"} 1 ${mockedHrTimeMs}\n` +
+            `test_sum{val="2"} 5 ${mockedHrTimeMs}\n` +
+            `test_bucket{val="2",le="1"} 0 ${mockedHrTimeMs}\n` +
+            `test_bucket{val="2",le="10"} 1 ${mockedHrTimeMs}\n` +
+            `test_bucket{val="2",le="100"} 1 ${mockedHrTimeMs}\n` +
+            `test_bucket{val="2",le="+Inf"} 1 ${mockedHrTimeMs}\n`
         );
       });
 
@@ -607,13 +607,13 @@ describe('PrometheusSerializer', () => {
       assert.strictEqual(
         result,
         'test_total{' +
-        'backslash="\u005c\u005c",' +
-        'doubleQuote="\u005c\u0022",' +
-        'lineFeed="\u005c\u006e",' +
-        'backslashN="\u005c\u005c\u006e",' +
-        'backslashDoubleQuote="\u005c\u005c\u005c\u0022",' +
-        'backslashLineFeed="\u005c\u005c\u005c\u006e"' +
-        `} 1 ${mockedHrTimeMs}\n`
+          'backslash="\u005c\u005c",' +
+          'doubleQuote="\u005c\u0022",' +
+          'lineFeed="\u005c\u006e",' +
+          'backslashN="\u005c\u005c\u006e",' +
+          'backslashDoubleQuote="\u005c\u005c\u005c\u0022",' +
+          'backslashLineFeed="\u005c\u005c\u005c\u006e"' +
+          `} 1 ${mockedHrTimeMs}\n`
       );
     });
 

From 7a30fead8eb34f5ea0b47777fc9ce8f606cc08c4 Mon Sep 17 00:00:00 2001
From: "marc.pichler" <marc.pichler@dynatrace.com>
Date: Mon, 10 Oct 2022 16:46:20 +0200
Subject: [PATCH 10/11] fix(exporter-prometheus): undo auto-formatting

---
 .../test/PrometheusSerializer.test.ts         | 24 +++++++++----------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts
index 627ddc7a9f..852946f355 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts
@@ -215,9 +215,9 @@ describe('PrometheusSerializer', () => {
         assert.strictEqual(
           result,
           '# HELP test_total foobar\n' +
-          '# TYPE test_total counter\n' +
-          `test_total{val="1"} 1 ${mockedHrTimeMs}\n` +
-          `test_total{val="2"} 1 ${mockedHrTimeMs}\n`
+            '# TYPE test_total counter\n' +
+            `test_total{val="1"} 1 ${mockedHrTimeMs}\n` +
+            `test_total{val="2"} 1 ${mockedHrTimeMs}\n`
         );
       });
 
@@ -227,9 +227,9 @@ describe('PrometheusSerializer', () => {
         assert.strictEqual(
           result,
           '# HELP test_total foobar\n' +
-          '# TYPE test_total counter\n' +
-          'test_total{val="1"} 1\n' +
-          'test_total{val="2"} 1\n'
+            '# TYPE test_total counter\n' +
+            'test_total{val="1"} 1\n' +
+            'test_total{val="2"} 1\n'
         );
       });
     });
@@ -266,9 +266,9 @@ describe('PrometheusSerializer', () => {
         assert.strictEqual(
           result,
           '# HELP test_total foobar\n' +
-            '# TYPE test_total gauge\n' +
-            `test_total{val="1"} 1 ${mockedHrTimeMs}\n` +
-            `test_total{val="2"} 1 ${mockedHrTimeMs}\n`
+          '# TYPE test_total gauge\n' +
+          `test_total{val="1"} 1 ${mockedHrTimeMs}\n` +
+          `test_total{val="2"} 1 ${mockedHrTimeMs}\n`
         );
       });
 
@@ -278,9 +278,9 @@ describe('PrometheusSerializer', () => {
         assert.strictEqual(
           result,
           '# HELP test_total foobar\n' +
-            '# TYPE test_total gauge\n' +
-            'test_total{val="1"} 1\n' +
-            'test_total{val="2"} 1\n'
+          '# TYPE test_total gauge\n' +
+          'test_total{val="1"} 1\n' +
+          'test_total{val="2"} 1\n'
         );
       });
     });

From b22e4cd075368ecda63b0130e7577545db2d8a90 Mon Sep 17 00:00:00 2001
From: "marc.pichler" <marc.pichler@dynatrace.com>
Date: Mon, 10 Oct 2022 17:13:44 +0200
Subject: [PATCH 11/11] feat(prometheus-exporter): move 'no metrics' comment to
 serializer

---
 .../src/PrometheusExporter.ts                        |  8 +-------
 .../src/PrometheusSerializer.ts                      | 12 ++++++++++--
 .../test/PrometheusExporter.test.ts                  |  2 +-
 3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts
index cbf20d0004..4f333eec55 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts
@@ -34,8 +34,6 @@ 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,
@@ -204,11 +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}`);
diff --git a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
index 065244a089..410cbfbf34 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts
@@ -168,6 +168,8 @@ function stringify(
   }\n`;
 }
 
+const NO_REGISTERED_METRICS = '# no registered metrics';
+
 export class PrometheusSerializer {
   private _prefix: string | undefined;
   private _appendTimestamp: boolean;
@@ -180,11 +182,17 @@ export class PrometheusSerializer {
   }
 
   serialize(resourceMetrics: ResourceMetrics): string {
-    let str = this._serializeResource(resourceMetrics.resource);
+    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) {
diff --git a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts
index 20a8d5b9ce..6b60952670 100644
--- a/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts
+++ b/experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusExporter.test.ts
@@ -352,7 +352,7 @@ describe('PrometheusExporter', () => {
 
       assert.deepStrictEqual(lines, [
         ...serializedEmptyResourceLines,
-        ''
+        '# no registered metrics'
       ]);
     });