Add OTLP proxy endpoint

Author: reakaleek

Directory.Packages.props

@@ -27,6 +27,7 @@
     <PackageVersion Include="AWSSDK.S3" Version="4.0.7.14" />
     <PackageVersion Include="Elastic.OpenTelemetry" Version="1.1.0" />
     <PackageVersion Include="Microsoft.Extensions.Configuration.UserSecrets" Version="10.0.0" />
+    <PackageVersion Include="Microsoft.Extensions.Configuration.Abstractions" Version="10.0.0" />
     <PackageVersion Include="Microsoft.Extensions.Telemetry.Abstractions" Version="10.0.0" />
     <PackageVersion Include="OpenTelemetry.Instrumentation.AspNetCore" Version="1.13.0" />
     <PackageVersion Include="Generator.Equals" Version="3.2.1" PrivateAssets="all" IncludeAssets="runtime; build; native; contentfiles; analyzers; buildtransitive" />
@@ -41,6 +42,7 @@
     <PackageVersion Include="Microsoft.OpenApi" Version="3.0.1" />
     <PackageVersion Include="TUnit" Version="0.25.21" />
     <PackageVersion Include="xunit.v3.extensibility.core" Version="2.0.2" />
+    <PackageVersion Include="WireMock.Net" Version="1.6.11" />
   </ItemGroup>
   <!-- Build -->
   <ItemGroup>
@@ -106,4 +108,4 @@
     </PackageVersion>
     <PackageVersion Include="xunit.v3" Version="2.0.2" />
   </ItemGroup>
-</Project>
+</Project>

src/api/Elastic.Documentation.Api.Core/Elastic.Documentation.Api.Core.csproj

@@ -9,6 +9,7 @@
     </PropertyGroup>
 
     <ItemGroup>
+      <PackageReference Include="Microsoft.Extensions.Configuration.Abstractions" />
       <PackageReference Include="Microsoft.Extensions.Logging" />
       <PackageReference Include="Microsoft.Extensions.Telemetry.Abstractions" />
     </ItemGroup>

src/api/Elastic.Documentation.Api.Core/Telemetry/IOtlpGateway.cs

@@ -0,0 +1,25 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+namespace Elastic.Documentation.Api.Core.Telemetry;
+
+/// <summary>
+/// Gateway for forwarding OTLP telemetry to a collector.
+/// </summary>
+public interface IOtlpGateway
+{
+	/// <summary>
+	/// Forwards OTLP telemetry data to the collector.
+	/// </summary>
+	/// <param name="signalType">The OTLP signal type: traces, logs, or metrics</param>
+	/// <param name="requestBody">The raw OTLP payload stream</param>
+	/// <param name="contentType">Content-Type of the payload</param>
+	/// <param name="ctx">Cancellation token</param>
+	/// <returns>HTTP status code and response content</returns>
+	Task<(int StatusCode, string? Content)> ForwardOtlp(
+		string signalType,
+		Stream requestBody,
+		string contentType,
+		Cancel ctx = default);
+}

src/api/Elastic.Documentation.Api.Core/Telemetry/OtlpProxyOptions.cs

@@ -0,0 +1,58 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using Microsoft.Extensions.Configuration;
+
+namespace Elastic.Documentation.Api.Core.Telemetry;
+
+/// <summary>
+/// Configuration options for the OTLP proxy.
+/// When using ADOT Lambda Layer, the proxy forwards to the local collector at localhost:4318.
+/// The ADOT layer handles authentication and forwarding to the backend (Elastic APM, etc).
+/// </summary>
+/// <remarks>
+/// ADOT Lambda Layer runs a local OpenTelemetry Collector that accepts OTLP/HTTP on:
+/// - localhost:4318 (HTTP/JSON and HTTP/protobuf)
+/// - localhost:4317 (gRPC)
+/// 
+/// The ADOT layer is configured via environment variables:
+/// - OTEL_EXPORTER_OTLP_ENDPOINT: Where ADOT forwards telemetry
+/// - OTEL_EXPORTER_OTLP_HEADERS: Authentication headers ADOT uses
+/// - AWS_LAMBDA_EXEC_WRAPPER: /opt/otel-instrument (enables ADOT)
+/// </remarks>
+public class OtlpProxyOptions
+{
+	/// <summary>
+	/// OTLP endpoint URL for the local ADOT collector.
+	/// Defaults to localhost:4318 when running in Lambda with ADOT layer.
+	/// </summary>
+	public string Endpoint { get; }
+
+	public OtlpProxyOptions(IConfiguration configuration)
+	{
+		// Check for test override first (for integration tests with WireMock)
+		var configEndpoint = configuration["OtlpProxy:Endpoint"];
+		if (!string.IsNullOrEmpty(configEndpoint))
+		{
+			Endpoint = configEndpoint;
+			return;
+		}
+
+		// Check if we're in Lambda with ADOT layer
+		var execWrapper = Environment.GetEnvironmentVariable("AWS_LAMBDA_EXEC_WRAPPER");
+		var isAdotEnabled = execWrapper?.Contains("otel-instrument") == true;
+
+		if (isAdotEnabled)
+		{
+			// ADOT Lambda Layer runs collector on localhost:4318
+			Endpoint = "http://localhost:4318";
+		}
+		else
+		{
+			// Fallback to configured endpoint for local development
+			Endpoint = Environment.GetEnvironmentVariable("OTEL_EXPORTER_OTLP_ENDPOINT")
+				?? "http://localhost:4318";
+		}
+	}
+}

src/api/Elastic.Documentation.Api.Core/Telemetry/OtlpProxyRequest.cs

@@ -0,0 +1,18 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+namespace Elastic.Documentation.Api.Core.Telemetry;
+
+/// <summary>
+/// Request model for OTLP proxy endpoint.
+/// Accepts raw OTLP payload from frontend and forwards to configured OTLP endpoint.
+/// </summary>
+public class OtlpProxyRequest
+{
+	/// <summary>
+	/// The OTLP signal type: traces, logs, or metrics
+	/// </summary>
+	public required string SignalType { get; init; }
+}
+

src/api/Elastic.Documentation.Api.Core/Telemetry/OtlpProxyUsecase.cs

@@ -0,0 +1,46 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using System.Diagnostics;
+using Microsoft.Extensions.Logging;
+
+namespace Elastic.Documentation.Api.Core.Telemetry;
+
+/// <summary>
+/// Proxies OTLP telemetry from the frontend to the local ADOT Lambda Layer collector.
+/// The ADOT layer handles authentication and forwarding to the backend.
+/// </summary>
+public class OtlpProxyUsecase(
+	IOtlpGateway gateway,
+	ILogger<OtlpProxyUsecase> logger)
+{
+	private static readonly ActivitySource ActivitySource = new(TelemetryConstants.OtlpProxySourceName);
+
+	/// <summary>
+	/// Proxies OTLP data from the frontend to the local ADOT collector.
+	/// </summary>
+	/// <param name="signalType">The OTLP signal type: traces, logs, or metrics</param>
+	/// <param name="requestBody">The raw OTLP payload (JSON or protobuf)</param>
+	/// <param name="contentType">Content-Type header from the original request</param>
+	/// <param name="ctx">Cancellation token</param>
+	/// <returns>HTTP status code and response content</returns>
+	public async Task<(int StatusCode, string? Content)> ProxyOtlp(
+		string signalType,
+		Stream requestBody,
+		string contentType,
+		Cancel ctx = default)
+	{
+		using var activity = ActivitySource.StartActivity("ProxyOtlp", ActivityKind.Client);
+
+		// Validate signal type
+		if (signalType is not ("traces" or "logs" or "metrics"))
+		{
+			logger.LogWarning("Invalid OTLP signal type: {SignalType}", signalType);
+			return (400, $"Invalid signal type: {signalType}. Must be traces, logs, or metrics");
+		}
+
+		// Forward to gateway
+		return await gateway.ForwardOtlp(signalType, requestBody, contentType, ctx);
+	}
+}