Minor fixes to metrics, prometheus examples (#3623)

.vscode/settings.json

@@ -1,5 +1,6 @@
 {
   "cSpell.words": [
+    "appsettings",
     "asax",
     "cijo",
     "cncf",
@@ -37,8 +38,8 @@
     "struct",
     "tbody",
     "thead",
-    "Tracestate",
     "tracestate",
+    "Tracestate",
     "triager",
     "umesan",
     "unencrypted",

examples/AspNetCore/Program.cs

@@ -27,7 +27,7 @@ var builder = WebApplication.CreateBuilder(args);
 // OpenTelemetry
 var assemblyVersion = Assembly.GetExecutingAssembly().GetName().Version?.ToString() ?? "unknown";
 
-// Switch between Zipkin/Jaeger/OTLP by setting UseExporter in appsettings.json.
+// Switch between Zipkin/Jaeger/OTLP/Console by setting UseTracingExporter in appsettings.json.
 var tracingExporter = builder.Configuration.GetValue<string>("UseTracingExporter").ToLowerInvariant();
 
 var serviceName = tracingExporter switch
@@ -90,6 +90,8 @@ builder.Logging.ClearProviders();
 builder.Logging.AddOpenTelemetry(options =>
 {
     options.ConfigureResource(configureResource);
+
+    // Switch between Console/OTLP by setting UseLogExporter in appsettings.json.
     var logExporter = builder.Configuration.GetValue<string>("UseLogExporter").ToLowerInvariant();
     switch (logExporter)
     {
@@ -113,7 +115,7 @@ builder.Services.Configure<OpenTelemetryLoggerOptions>(opt =>
 });
 
 // Metrics
-
+// Switch between Prometheus/OTLP/Console by setting UseMetricsExporter in appsettings.json.
 var metricsExporter = builder.Configuration.GetValue<string>("UseMetricsExporter").ToLowerInvariant();
 
 builder.Services.AddOpenTelemetryMetrics(options =>

examples/AspNetCore/appsettings.json

@@ -17,9 +17,6 @@
     "Endpoint": "http://localhost:14268",
     "Protocol": "UdpCompactThrift"
   },
-  "Prometheus": {
-    "ScrapeResponseCacheDurationMilliseconds": 5000
-  },
   "Zipkin": {
     "ServiceName": "zipkin-test",
     "Endpoint": "http://localhost:9411/api/v2/spans"

src/OpenTelemetry.Exporter.Prometheus.AspNetCore/README.md

@@ -47,18 +47,13 @@ dotnet add package --prerelease OpenTelemetry.Exporter.Prometheus.AspNetCore
 ### Step 3: Configure Prometheus Scraping Endpoint
 
 * Register Prometheus scraping middleware using the
-  `UseOpenTelemetryPrometheusScrapingEndpoint` extension:
+  `UseOpenTelemetryPrometheusScrapingEndpoint` extension method
+  on `IApplicationBuilder` :
 
     ```csharp
-    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
-    {
-        app.UseOpenTelemetryPrometheusScrapingEndpoint();
-        app.UseRouting();
-        app.UseEndpoints(endpoints =>
-        {
-            endpoints.MapControllers();
-        });
-    }
+    var builder = WebApplication.CreateBuilder(args);
+    var app = builder.Build();
+    app.UseOpenTelemetryPrometheusScrapingEndpoint();
     ```
 
     Overloads of the `UseOpenTelemetryPrometheusScrapingEndpoint` extension are
@@ -66,17 +61,9 @@ dotnet add package --prerelease OpenTelemetry.Exporter.Prometheus.AspNetCore
     function can be used:
 
     ```csharp
-    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
-    {
-        app.UseOpenTelemetryPrometheusScrapingEndpoint(
+    app.UseOpenTelemetryPrometheusScrapingEndpoint(
             context => context.Request.Path == "/internal/metrics"
                 && context.Connection.LocalPort == 5067);
-        app.UseRouting();
-        app.UseEndpoints(endpoints =>
-        {
-            endpoints.MapControllers();
-        });
-    }
     ```
 
 ## Configuration

src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusSerializerExt.cs

@@ -23,6 +23,12 @@ namespace OpenTelemetry.Exporter.Prometheus
     /// </summary>
     internal static partial class PrometheusSerializer
     {
+        /* Counter becomes counter
+           Gauge becomes gauge
+           Histogram becomes histogram
+           UpDownCounter becomes gauge
+         * https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/data-model.md#otlp-metric-points-to-prometheus
+        */
         private static readonly string[] MetricTypes = new string[]
         {
             "untyped", "counter", "gauge", "summary", "histogram", "histogram", "histogram", "histogram", "gauge",

src/OpenTelemetry/Metrics/MetricReader.cs

@@ -41,7 +41,7 @@ namespace OpenTelemetry.Metrics
                 var type when type == typeof(ObservableCounter<>) => AggregationTemporality.Delta,
                 var type when type == typeof(Histogram<>) => AggregationTemporality.Delta,
 
-                // Temporatlity is not defined for gauges, so this does not really affect anything.
+                // Temporality is not defined for gauges, so this does not really affect anything.
                 var type when type == typeof(ObservableGauge<>) => AggregationTemporality.Delta,
 
                 var type when type == typeof(UpDownCounter<>) => AggregationTemporality.Cumulative,