Add OTLP exporter support alongside Azure Monitor

Botello.csproj

@@ -14,7 +14,7 @@
     <!-- Prevent MSBuild from loading this assembly as a build task -->
     <GenerateAssemblyInfo>true</GenerateAssemblyInfo>
 
-    <Description>MSBuild custom logger that forwards build events to Azure Application Insights via OpenTelemetry.</Description>
+    <Description>MSBuild custom logger that forwards build events to Azure Application Insights or any OTLP-compatible backend via OpenTelemetry.</Description>
     <Authors>Botello</Authors>
   </PropertyGroup>
 
@@ -30,8 +30,9 @@
     <PackageReference Include="Microsoft.Build.Framework" Version="18.3.3" />
     <PackageReference Include="Microsoft.Build.Utilities.Core" Version="18.3.3" />
 
-    <!-- OpenTelemetry + Azure Monitor exporter (covers both logs and traces) -->
+    <!-- OpenTelemetry + exporters (Azure Monitor and OTLP) -->
     <PackageReference Include="Azure.Monitor.OpenTelemetry.Exporter" Version="1.6.0" />
+    <PackageReference Include="OpenTelemetry.Exporter.OpenTelemetryProtocol" Version="1.15.0" />
     <PackageReference Include="OpenTelemetry.Extensions.Hosting" Version="1.15.0" />
 
     <!-- Configuration: JSON file + environment variables -->

Config/ConfigurationLoader.cs

@@ -56,8 +56,43 @@ private static void ApplyLoggerParameters(string parameters, LoggerConfig config
             if (string.IsNullOrEmpty(value))
                 continue;
 
-            if (key.Equals("ConnectionString", StringComparison.OrdinalIgnoreCase))
+            // ── Exporter selection ──────────────────────────────────────
+            if (key.Equals("Exporter", StringComparison.OrdinalIgnoreCase))
+            {
+                if (Enum.TryParse(value, ignoreCase: true, out ExporterType exporter))
+                    config.Exporter = exporter;
+                else
+                    throw new InvalidOperationException(
+                        $"Botello: Unknown Exporter value '{value}'. " +
+                        "Valid values: AzureMonitor, Otlp.");
+            }
+            // ── Azure Monitor ───────────────────────────────────────────
+            else if (key.Equals("ConnectionString", StringComparison.OrdinalIgnoreCase))
                 config.ConnectionString = value;
+            // ── OTLP ────────────────────────────────────────────────────
+            else if (key.Equals("OtlpEndpoint", StringComparison.OrdinalIgnoreCase))
+                config.OtlpEndpoint = value;
+            else if (key.Equals("OtlpProtocol", StringComparison.OrdinalIgnoreCase))
+            {
+                if (Enum.TryParse(value, ignoreCase: true, out OtlpProtocolType protocol))
+                    config.OtlpProtocol = protocol;
+                else
+                    throw new InvalidOperationException(
+                        $"Botello: Unknown OtlpProtocol value '{value}'. " +
+                        "Valid values: Grpc, HttpProtobuf.");
+            }
+            else if (key.Equals("OtlpHeaders", StringComparison.OrdinalIgnoreCase))
+                config.OtlpHeaders = value;
+            else if (key.Equals("OtlpTimeout", StringComparison.OrdinalIgnoreCase))
+            {
+                if (int.TryParse(value, out var timeout) && timeout > 0)
+                    config.OtlpTimeout = timeout;
+                else
+                    throw new InvalidOperationException(
+                        $"Botello: Invalid OtlpTimeout value '{value}'. " +
+                        "Provide a positive integer (milliseconds).");
+            }
+            // ── Common ──────────────────────────────────────────────────
             else if (key.Equals("ServiceName", StringComparison.OrdinalIgnoreCase))
                 config.ServiceName = value;
             else if (key.Equals("MinimumLevel", StringComparison.OrdinalIgnoreCase))

Config/LoggerConfig.cs

@@ -2,16 +2,80 @@
 
 namespace Botello.Config;
 
+/// <summary>
+/// Selects the telemetry export back-end.
+/// </summary>
+public enum ExporterType
+{
+    /// <summary>Azure Application Insights via the Azure Monitor exporter.</summary>
+    AzureMonitor,
+
+    /// <summary>Any OTLP-compatible collector (Jaeger, Grafana, Seq, Aspire Dashboard, etc.).</summary>
+    Otlp,
+}
+
+/// <summary>
+/// Selects the OTLP transport protocol. Only relevant when <see cref="LoggerConfig.Exporter"/>
+/// is set to <see cref="ExporterType.Otlp"/>.
+/// </summary>
+public enum OtlpProtocolType
+{
+    /// <summary>gRPC transport (default OTLP port 4317).</summary>
+    Grpc,
+
+    /// <summary>HTTP/protobuf transport (default OTLP port 4318).</summary>
+    HttpProtobuf,
+}
+
 /// <summary>
 /// Configuration for the Botello logger.
 /// Loaded from appsettings.json, environment variables (BOTELLO__*), and Logger.Parameters.
 /// </summary>
 public sealed class LoggerConfig
 {
-    /// <summary>Azure Application Insights connection string. Required.</summary>
+    // ── Exporter selection ──────────────────────────────────────────────
+
+    /// <summary>
+    /// Selects the telemetry back-end. Defaults to <see cref="ExporterType.AzureMonitor"/>.
+    /// Set to <see cref="ExporterType.Otlp"/> to export to any OTLP-compatible collector.
+    /// </summary>
+    public ExporterType Exporter { get; set; } = ExporterType.AzureMonitor;
+
+    // ── Azure Monitor settings ──────────────────────────────────────────
+
+    /// <summary>Azure Application Insights connection string. Required when Exporter is AzureMonitor.</summary>
     public string? ConnectionString { get; set; }
 
-    /// <summary>Service name reported in Application Insights. Defaults to "Botello".</summary>
+    // ── OTLP settings ───────────────────────────────────────────────────
+
+    /// <summary>
+    /// OTLP collector endpoint. Defaults to <c>http://localhost:4317</c> for gRPC
+    /// or <c>http://localhost:4318</c> for HTTP/protobuf. Only used when Exporter is Otlp.
+    /// </summary>
+    public string? OtlpEndpoint { get; set; }
+
+    /// <summary>
+    /// OTLP transport protocol. Defaults to <see cref="OtlpProtocolType.Grpc"/>.
+    /// Only used when Exporter is Otlp.
+    /// </summary>
+    public OtlpProtocolType OtlpProtocol { get; set; } = OtlpProtocolType.Grpc;
+
+    /// <summary>
+    /// Optional headers sent with every OTLP export request (comma-separated key=value pairs).
+    /// Example: <c>Authorization=Bearer token123,X-Custom=value</c>.
+    /// Only used when Exporter is Otlp.
+    /// </summary>
+    public string? OtlpHeaders { get; set; }
+
+    /// <summary>
+    /// Timeout in milliseconds for OTLP export requests. Defaults to 10 000 (10 s).
+    /// Only used when Exporter is Otlp.
+    /// </summary>
+    public int OtlpTimeout { get; set; } = 10_000;
+
+    // ── Common settings ─────────────────────────────────────────────────
+
+    /// <summary>Service name reported in telemetry. Defaults to "Botello".</summary>
     public string ServiceName { get; set; } = "Botello";
 
     /// <summary>Minimum log level to emit. Defaults to <see cref="LogLevel.Information"/>.</summary>
@@ -34,13 +98,18 @@ public sealed class LoggerConfig
 
     internal void Validate()
     {
-        if (string.IsNullOrWhiteSpace(ConnectionString))
-            throw new InvalidOperationException(
-                "Botello: A connection string for Application Insights is required. " +
-                "Provide it via appsettings.json (Botello:ConnectionString), " +
-                "the APPLICATIONINSIGHTS_CONNECTION_STRING or BOTELLO__CONNECTIONSTRING " +
-                "environment variable, or the Logger.Parameters CLI argument " +
-                "(-logger:Botello.dll;ConnectionString=...).");
+        if (Exporter == ExporterType.AzureMonitor)
+        {
+            if (string.IsNullOrWhiteSpace(ConnectionString))
+                throw new InvalidOperationException(
+                    "Botello: A connection string for Application Insights is required when " +
+                    "Exporter is AzureMonitor. Provide it via appsettings.json (Botello:ConnectionString), " +
+                    "the APPLICATIONINSIGHTS_CONNECTION_STRING or BOTELLO__CONNECTIONSTRING " +
+                    "environment variable, or the Logger.Parameters CLI argument " +
+                    "(-logger:Botello.dll;ConnectionString=...).");
+        }
+
+        // OTLP does not strictly require an endpoint — it falls back to localhost defaults.
 
         if (string.IsNullOrWhiteSpace(ServiceName))
             ServiceName = "Botello";