Enable zipkin endpoint configuration via environment variable

src/OpenTelemetry.Exporter.Zipkin/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+* Enabling endpoint configuration in ZipkinExporterOptions via
+  `OTEL_EXPORTER_ZIPKIN_ENDPOINT` environment variable.
+  ([#1453](https://github.com/open-telemetry/opentelemetry-dotnet/issues/1453))
+
 ## 1.1.0-rc1
 
 Released 2021-Jun-25

src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinExporterEventSource.cs

@@ -37,10 +37,25 @@ public void FailedExport(Exception ex)
             }
         }
 
+        [NonEvent]
+        public void FailedEndpointInitialization(Exception ex)
+        {
+            if (this.IsEnabled(EventLevel.Error, (EventKeywords)(-1)))
+            {
+                this.FailedEndpointInitialization(ex.ToInvariantString());
+            }
+        }
+
         [Event(1, Message = "Failed to export activities: '{0}'", Level = EventLevel.Error)]
         public void FailedExport(string exception)
         {
             this.WriteEvent(1, exception);
         }
+
+        [Event(2, Message = "Error initializing Zipkin endpoint, falling back to default value: '{0}'", Level = EventLevel.Error)]
+        public void FailedEndpointInitialization(string exception)
+        {
+            this.WriteEvent(2, exception);
+        }
     }
 }

src/OpenTelemetry.Exporter.Zipkin/README.md

@@ -27,6 +27,12 @@ You can configure the `ZipkinExporter` through
    associated with the telemetry has "service.name" defined, then it'll be
    preferred over this option.
 * `Endpoint`: URI address to receive telemetry (default `http://localhost:9411/api/v2/spans`).
+
+   The endpoint configuration can be provided either [via code](../../examples/Console/TestZipkinExporter.cs)
+    or
+   [via environment variable](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/sdk-environment-variables.md#zipkin-exporter),
+    with code taking precedence over environment variable.
+
 * `UseShortTraceIds`: Whether the trace's ID should be shortened before
    sending to Zipkin (default false).
 * `MaxPayloadSizeInBytes`: Maximum payload size - for .NET versions

src/OpenTelemetry.Exporter.Zipkin/ZipkinExporterOptions.cs

@@ -16,6 +16,7 @@
 
 using System;
 using System.Diagnostics;
+using OpenTelemetry.Exporter.Zipkin.Implementation;
 
 namespace OpenTelemetry.Exporter
 {
@@ -27,12 +28,31 @@ public sealed class ZipkinExporterOptions
 #if !NET452
         internal const int DefaultMaxPayloadSizeInBytes = 4096;
 #endif
+        internal const string ZipkinEndpointEnvVar = "OTEL_EXPORTER_ZIPKIN_ENDPOINT";
+        internal const string DefaultZipkinEndpoint = "http://localhost:9411/api/v2/spans";
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ZipkinExporterOptions"/> class.
+        /// Initializes zipkin endpoint.
+        /// </summary>
+        public ZipkinExporterOptions()
+        {
+            try
+            {
+                this.Endpoint = new Uri(Environment.GetEnvironmentVariable(ZipkinEndpointEnvVar) ?? DefaultZipkinEndpoint);
+            }
+            catch (Exception ex)
+            {
+                this.Endpoint = new Uri(DefaultZipkinEndpoint);
+                ZipkinExporterEventSource.Log.FailedEndpointInitialization(ex);
+            }
+        }
 
         /// <summary>
         /// Gets or sets Zipkin endpoint address. See https://zipkin.io/zipkin-api/#/default/post_spans.
         /// Typically https://zipkin-server-name:9411/api/v2/spans.
         /// </summary>
-        public Uri Endpoint { get; set; } = new Uri("http://localhost:9411/api/v2/spans");
+        public Uri Endpoint { get; set; }
 
         /// <summary>
         /// Gets or sets a value indicating whether short trace id should be used.

test/OpenTelemetry.Exporter.Zipkin.Tests/ZipkinExporterTests.cs

@@ -131,6 +131,60 @@ public void SuppresssesInstrumentation()
             Assert.Equal(1, endCalledCount);
         }
 
+        [Fact]
+        public void EndpointConfigurationUsingEnvironmentVariable()
+        {
+            try
+            {
+                Environment.SetEnvironmentVariable(ZipkinExporterOptions.ZipkinEndpointEnvVar, "http://urifromenvironmentvariable");
+
+                var exporterOptions = new ZipkinExporterOptions();
+
+                Assert.Equal(new Uri(Environment.GetEnvironmentVariable(ZipkinExporterOptions.ZipkinEndpointEnvVar)).AbsoluteUri, exporterOptions.Endpoint.AbsoluteUri);
+            }
+            finally
+            {
+                Environment.SetEnvironmentVariable(ZipkinExporterOptions.ZipkinEndpointEnvVar, null);
+            }
+        }
+
+        [Fact]
+        public void IncodeEndpointConfigTakesPrecedenceOverEnvironmentVariable()
+        {
+            try
+            {
+                Environment.SetEnvironmentVariable(ZipkinExporterOptions.ZipkinEndpointEnvVar, "http://urifromenvironmentvariable");
+
+                var exporterOptions = new ZipkinExporterOptions
+                {
+                    Endpoint = new Uri("http://urifromcode"),
+                };
+
+                Assert.Equal(new Uri("http://urifromcode").AbsoluteUri, exporterOptions.Endpoint.AbsoluteUri);
+            }
+            finally
+            {
+                Environment.SetEnvironmentVariable(ZipkinExporterOptions.ZipkinEndpointEnvVar, null);
+            }
+        }
+
+        [Fact]
+        public void ErrorGettingUriFromEnvVarSetsDefaultEndpointValue()
+        {
+            try
+            {
+                Environment.SetEnvironmentVariable(ZipkinExporterOptions.ZipkinEndpointEnvVar, "InvalidUri");
+
+                var exporterOptions = new ZipkinExporterOptions();
+
+                Assert.Equal(new Uri(ZipkinExporterOptions.DefaultZipkinEndpoint).AbsoluteUri, exporterOptions.Endpoint.AbsoluteUri);
+            }
+            finally
+            {
+                Environment.SetEnvironmentVariable(ZipkinExporterOptions.ZipkinEndpointEnvVar, null);
+            }
+        }
+
         [Theory]
         [InlineData(true, false, false)]
         [InlineData(false, false, false)]