[prometheus] Support meter-level tags (#5837)

Co-authored-by: Cijo Thomas <[email protected]>
open-telemetry · Sep 23, 2024 · 60b7d9b · 60b7d9b
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diff --git a/src/OpenTelemetry.Exporter.Prometheus.AspNetCore/CHANGELOG.md b/src/OpenTelemetry.Exporter.Prometheus.AspNetCore/CHANGELOG.md
@@ -7,6 +7,9 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+* Added meter-level tags to Prometheus exporter
+  ([#5837](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5837))
+
 ## 1.9.0-beta.2
 
 Released 2024-Jun-24

diff --git a/src/OpenTelemetry.Exporter.Prometheus.HttpListener/CHANGELOG.md b/src/OpenTelemetry.Exporter.Prometheus.HttpListener/CHANGELOG.md
@@ -7,6 +7,9 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+* Added meter-level tags to Prometheus exporter
+  ([#5837](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5837))
+
 ## 1.9.0-beta.2
 
 Released 2024-Jun-24

diff --git a/src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusSerializer.cs b/src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusSerializer.cs
@@ -404,6 +404,15 @@ public static int WriteTags(byte[] buffer, int cursor, Metric metric, ReadOnlyTa
             buffer[cursor++] = unchecked((byte)',');
         }
 
+        if (metric.MeterTags != null)
+        {
+            foreach (var tag in metric.MeterTags)
+            {
+                cursor = WriteLabel(buffer, cursor, tag.Key, tag.Value);
+                buffer[cursor++] = unchecked((byte)',');
+            }
+        }
+
         foreach (var tag in tags)
         {
             cursor = WriteLabel(buffer, cursor, tag.Key, tag.Value);

diff --git a/test/OpenTelemetry.Exporter.Prometheus.AspNetCore.Tests/PrometheusExporterMiddlewareTests.cs b/test/OpenTelemetry.Exporter.Prometheus.AspNetCore.Tests/PrometheusExporterMiddlewareTests.cs
@@ -249,43 +249,53 @@ public Task PrometheusExporterMiddlewareIntegration_UseOpenMetricsVersionHeader(
     }
 
     [Fact]
-    public async Task PrometheusExporterMiddlewareIntegration_CanServeOpenMetricsAndPlainFormats()
+    public Task PrometheusExporterMiddlewareIntegration_TextPlainResponse_WithMeterTags()
     {
-        using var host = await StartTestHostAsync(
-            app => app.UseOpenTelemetryPrometheusScrapingEndpoint());
-
-        var tags = new KeyValuePair<string, object?>[]
+        var meterTags = new KeyValuePair<string, object?>[]
         {
-            new("key1", "value1"),
-            new("key2", "value2"),
+            new("meterKey1", "value1"),
+            new("meterKey2", "value2"),
         };
 
-        using var meter = new Meter(MeterName, MeterVersion);
-
-        var beginTimestamp = DateTimeOffset.Now.ToUnixTimeMilliseconds();
+        return RunPrometheusExporterMiddlewareIntegrationTest(
+            "/metrics",
+            app => app.UseOpenTelemetryPrometheusScrapingEndpoint(),
+            acceptHeader: "text/plain",
+            meterTags: meterTags);
+    }
 
-        var counter = meter.CreateCounter<double>("counter_double", unit: "By");
-        counter.Add(100.18D, tags);
-        counter.Add(0.99D, tags);
+    [Fact]
+    public Task PrometheusExporterMiddlewareIntegration_UseOpenMetricsVersionHeader_WithMeterTags()
+    {
+        var meterTags = new KeyValuePair<string, object?>[]
+        {
+            new("meterKey1", "value1"),
+            new("meterKey2", "value2"),
+        };
 
-        var testCases = new bool[] { true, false, true, true, false };
+        return RunPrometheusExporterMiddlewareIntegrationTest(
+            "/metrics",
+            app => app.UseOpenTelemetryPrometheusScrapingEndpoint(),
+            acceptHeader: "application/openmetrics-text; version=1.0.0",
+            meterTags: meterTags);
+    }
 
-        using var client = host.GetTestClient();
+    [Fact]
+    public async Task PrometheusExporterMiddlewareIntegration_CanServeOpenMetricsAndPlainFormats_NoMeterTags()
+    {
+        await RunPrometheusExporterMiddlewareIntegrationTestWithBothFormats();
+    }
 
-        foreach (var testCase in testCases)
+    [Fact]
+    public async Task PrometheusExporterMiddlewareIntegration_CanServeOpenMetricsAndPlainFormats_WithMeterTags()
+    {
+        var meterTags = new KeyValuePair<string, object?>[]
         {
-            using var request = new HttpRequestMessage
-            {
-                Headers = { { "Accept", testCase ? "application/openmetrics-text" : "text/plain" } },
-                RequestUri = new Uri("/metrics", UriKind.Relative),
-                Method = HttpMethod.Get,
-            };
-            using var response = await client.SendAsync(request);
-            var endTimestamp = DateTimeOffset.Now.ToUnixTimeMilliseconds();
-            await VerifyAsync(beginTimestamp, endTimestamp, response, testCase);
-        }
+            new("meterKey1", "value1"),
+            new("meterKey2", "value2"),
+        };
 
-        await host.StopAsync();
+        await RunPrometheusExporterMiddlewareIntegrationTestWithBothFormats(meterTags);
     }
 
     [Fact]
@@ -312,6 +322,45 @@ public async Task PrometheusExporterMiddlewareIntegration_TestBufferSizeIncrease
         await host.StopAsync();
     }
 
+    private static async Task RunPrometheusExporterMiddlewareIntegrationTestWithBothFormats(KeyValuePair<string, object?>[]? meterTags = null)
+    {
+        using var host = await StartTestHostAsync(
+            app => app.UseOpenTelemetryPrometheusScrapingEndpoint());
+
+        var counterTags = new KeyValuePair<string, object?>[]
+        {
+            new("key1", "value1"),
+            new("key2", "value2"),
+        };
+
+        using var meter = new Meter(MeterName, MeterVersion, meterTags);
+
+        var beginTimestamp = DateTimeOffset.Now.ToUnixTimeMilliseconds();
+
+        var counter = meter.CreateCounter<double>("counter_double", unit: "By");
+        counter.Add(100.18D, counterTags);
+        counter.Add(0.99D, counterTags);
+
+        var testCases = new bool[] { true, false, true, true, false };
+
+        using var client = host.GetTestClient();
+
+        foreach (var testCase in testCases)
+        {
+            using var request = new HttpRequestMessage
+            {
+                Headers = { { "Accept", testCase ? "application/openmetrics-text" : "text/plain" } },
+                RequestUri = new Uri("/metrics", UriKind.Relative),
+                Method = HttpMethod.Get,
+            };
+            using var response = await client.SendAsync(request);
+            var endTimestamp = DateTimeOffset.Now.ToUnixTimeMilliseconds();
+            await VerifyAsync(beginTimestamp, endTimestamp, response, testCase, meterTags);
+        }
+
+        await host.StopAsync();
+    }
+
     private static async Task RunPrometheusExporterMiddlewareIntegrationTest(
         string path,
         Action<IApplicationBuilder> configure,
@@ -320,27 +369,28 @@ private static async Task RunPrometheusExporterMiddlewareIntegrationTest(
         bool registerMeterProvider = true,
         Action<PrometheusAspNetCoreOptions>? configureOptions = null,
         bool skipMetrics = false,
-        string acceptHeader = "application/openmetrics-text")
+        string acceptHeader = "application/openmetrics-text",
+        KeyValuePair<string, object?>[]? meterTags = null)
     {
         var requestOpenMetrics = acceptHeader.StartsWith("application/openmetrics-text");
 
         using var host = await StartTestHostAsync(configure, configureServices, registerMeterProvider, configureOptions);
 
-        var tags = new KeyValuePair<string, object?>[]
+        var counterTags = new KeyValuePair<string, object?>[]
         {
             new("key1", "value1"),
             new("key2", "value2"),
         };
 
-        using var meter = new Meter(MeterName, MeterVersion);
+        using var meter = new Meter(MeterName, MeterVersion, meterTags);
 
         var beginTimestamp = DateTimeOffset.Now.ToUnixTimeMilliseconds();
 
         var counter = meter.CreateCounter<double>("counter_double", unit: "By");
         if (!skipMetrics)
         {
-            counter.Add(100.18D, tags);
-            counter.Add(0.99D, tags);
+            counter.Add(100.18D, counterTags);
+            counter.Add(0.99D, counterTags);
         }
 
         using var client = host.GetTestClient();
@@ -356,7 +406,7 @@ private static async Task RunPrometheusExporterMiddlewareIntegrationTest(
 
         if (!skipMetrics)
         {
-            await VerifyAsync(beginTimestamp, endTimestamp, response, requestOpenMetrics);
+            await VerifyAsync(beginTimestamp, endTimestamp, response, requestOpenMetrics, meterTags);
         }
         else
         {
@@ -368,7 +418,7 @@ private static async Task RunPrometheusExporterMiddlewareIntegrationTest(
         await host.StopAsync();
     }
 
-    private static async Task VerifyAsync(long beginTimestamp, long endTimestamp, HttpResponseMessage response, bool requestOpenMetrics)
+    private static async Task VerifyAsync(long beginTimestamp, long endTimestamp, HttpResponseMessage response, bool requestOpenMetrics, KeyValuePair<string, object?>[]? meterTags)
     {
         Assert.Equal(HttpStatusCode.OK, response.StatusCode);
         Assert.True(response.Content.Headers.Contains("Last-Modified"));
@@ -382,6 +432,10 @@ private static async Task VerifyAsync(long beginTimestamp, long endTimestamp, Ht
             Assert.Equal("text/plain; charset=utf-8; version=0.0.4", response.Content.Headers.ContentType!.ToString());
         }
 
+        var additionalTags = meterTags != null && meterTags.Any()
+            ? $"{string.Join(",", meterTags.Select(x => $"{x.Key}=\"{x.Value}\""))},"
+            : string.Empty;
+
         string content = (await response.Content.ReadAsStringAsync()).ReplaceLineEndings();
 
         string expected = requestOpenMetrics
@@ -394,14 +448,14 @@ private static async Task VerifyAsync(long beginTimestamp, long endTimestamp, Ht
                     otel_scope_info{otel_scope_name="{{MeterName}}"} 1
                     # TYPE counter_double_bytes counter
                     # UNIT counter_double_bytes bytes
-                    counter_double_bytes_total{otel_scope_name="{{MeterName}}",otel_scope_version="{{MeterVersion}}",key1="value1",key2="value2"} 101.17 (\d+\.\d{3})
+                    counter_double_bytes_total{otel_scope_name="{{MeterName}}",otel_scope_version="{{MeterVersion}}",{{additionalTags}}key1="value1",key2="value2"} 101.17 (\d+\.\d{3})
                     # EOF
 
                     """.ReplaceLineEndings()
             : $$"""
                     # TYPE counter_double_bytes_total counter
                     # UNIT counter_double_bytes_total bytes
-                    counter_double_bytes_total{otel_scope_name="{{MeterName}}",otel_scope_version="{{MeterVersion}}",key1="value1",key2="value2"} 101.17 (\d+)
+                    counter_double_bytes_total{otel_scope_name="{{MeterName}}",otel_scope_version="{{MeterVersion}}",{{additionalTags}}key1="value1",key2="value2"} 101.17 (\d+)
                     # EOF
 
                     """.ReplaceLineEndings();

diff --git a/test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/PrometheusHttpListenerTests.cs b/test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/PrometheusHttpListenerTests.cs
@@ -84,6 +84,30 @@ public async Task PrometheusExporterHttpServerIntegration_UseOpenMetricsVersionH
         await this.RunPrometheusExporterHttpServerIntegrationTest(acceptHeader: "application/openmetrics-text; version=1.0.0");
     }
 
+    [Fact]
+    public async Task PrometheusExporterHttpServerIntegration_NoOpenMetrics_WithMeterTags()
+    {
+        var tags = new KeyValuePair<string, object?>[]
+        {
+            new("meter1", "value1"),
+            new("meter2", "value2"),
+        };
+
+        await this.RunPrometheusExporterHttpServerIntegrationTest(acceptHeader: string.Empty, meterTags: tags);
+    }
+
+    [Fact]
+    public async Task PrometheusExporterHttpServerIntegration_OpenMetrics_WithMeterTags()
+    {
+        var tags = new KeyValuePair<string, object?>[]
+        {
+            new("meter1", "value1"),
+            new("meter2", "value2"),
+        };
+
+        await this.RunPrometheusExporterHttpServerIntegrationTest(acceptHeader: "application/openmetrics-text; version=1.0.0", meterTags: tags);
+    }
+
     [Fact]
     public void PrometheusHttpListenerThrowsOnStart()
     {
@@ -236,15 +260,15 @@ private static MeterProvider BuildMeterProvider(Meter meter, IEnumerable<KeyValu
         return provider;
     }
 
-    private async Task RunPrometheusExporterHttpServerIntegrationTest(bool skipMetrics = false, string acceptHeader = "application/openmetrics-text")
+    private async Task RunPrometheusExporterHttpServerIntegrationTest(bool skipMetrics = false, string acceptHeader = "application/openmetrics-text", KeyValuePair<string, object?>[]? meterTags = null)
     {
         var requestOpenMetrics = acceptHeader.StartsWith("application/openmetrics-text");
 
-        using var meter = new Meter(MeterName, MeterVersion);
+        using var meter = new Meter(MeterName, MeterVersion, meterTags);
 
         var provider = BuildMeterProvider(meter, [], out var address);
 
-        var tags = new KeyValuePair<string, object?>[]
+        var counterTags = new KeyValuePair<string, object?>[]
         {
             new("key1", "value1"),
             new("key2", "value2"),
@@ -253,8 +277,8 @@ private async Task RunPrometheusExporterHttpServerIntegrationTest(bool skipMetri
         var counter = meter.CreateCounter<double>("counter_double", unit: "By");
         if (!skipMetrics)
         {
-            counter.Add(100.18D, tags);
-            counter.Add(0.99D, tags);
+            counter.Add(100.18D, counterTags);
+            counter.Add(0.99D, counterTags);
         }
 
         using HttpClient client = new HttpClient();
@@ -280,6 +304,10 @@ private async Task RunPrometheusExporterHttpServerIntegrationTest(bool skipMetri
                 Assert.Equal("text/plain; charset=utf-8; version=0.0.4", response.Content.Headers.ContentType!.ToString());
             }
 
+            var additionalTags = meterTags != null && meterTags.Any()
+                ? $"{string.Join(",", meterTags.Select(x => $"{x.Key}='{x.Value}'"))},"
+                : string.Empty;
+
             var content = await response.Content.ReadAsStringAsync();
 
             var expected = requestOpenMetrics
@@ -291,11 +319,11 @@ private async Task RunPrometheusExporterHttpServerIntegrationTest(bool skipMetri
                   + $"otel_scope_info{{otel_scope_name='{MeterName}'}} 1\n"
                   + "# TYPE counter_double_bytes counter\n"
                   + "# UNIT counter_double_bytes bytes\n"
-                  + $"counter_double_bytes_total{{otel_scope_name='{MeterName}',otel_scope_version='{MeterVersion}',key1='value1',key2='value2'}} 101.17 (\\d+\\.\\d{{3}})\n"
+                  + $"counter_double_bytes_total{{otel_scope_name='{MeterName}',otel_scope_version='{MeterVersion}',{additionalTags}key1='value1',key2='value2'}} 101.17 (\\d+\\.\\d{{3}})\n"
                   + "# EOF\n"
                 : "# TYPE counter_double_bytes_total counter\n"
                   + "# UNIT counter_double_bytes_total bytes\n"
-                  + $"counter_double_bytes_total{{otel_scope_name='{MeterName}',otel_scope_version='{MeterVersion}',key1='value1',key2='value2'}} 101.17 (\\d+)\n"
+                  + $"counter_double_bytes_total{{otel_scope_name='{MeterName}',otel_scope_version='{MeterVersion}',{additionalTags}key1='value1',key2='value2'}} 101.17 (\\d+)\n"
                   + "# EOF\n";
 
             Assert.Matches(("^" + expected + "$").Replace('\'', '"'), content);