OpenTelemetry observability for .NET 10 applications. Covers traces, metrics, and logs using the OpenTelemetry SDK with OTLP export. Includes custom ActivitySource, IMeterFactory metrics, resource configuration, and Aspire Dashboard integration. Load this skill when setting up distributed tracing, custom metrics, OTLP export, or when the user mentions "OpenTelemetry", "OTLP", "traces", "spans", "Activity", "ActivitySource", "metrics", "IMeterFactory", "Meter", "Counter", "Histogram", "Gauge", "telemetry", "observability", "distributed tracing", "OTEL", or "Aspire Dashboard".
Three pillars, one setup — Configure traces, metrics, and logs through a single AddOpenTelemetry() call. Use UseOtlpExporter() for cross-cutting export to any OTLP-compatible backend.
Use IMeterFactory for metrics — Never create Meter instances with new. The factory manages lifetime through DI and prevents leaks.
Null-safe activities — StartActivity() returns null when no listener is attached. Always use ?. when setting tags or events.
Environment variables over code — Use OTEL_EXPORTER_OTLP_ENDPOINT and OTEL_SERVICE_NAME so deployments control telemetry routing without code changes.
Low-cardinality metric tags — Keep metric tag combinations under ~1000 per instrument. Use span attributes or logs for high-cardinality data like user IDs or request IDs.
Patterns
Full Setup with All Three Signals
// Program.cs
var builder = WebApplication.CreateBuilder(args);
