OpenTelemetry Integration

SlimFaas provides built-in support for OpenTelemetry, enabling comprehensive observability of your serverless functions through distributed tracing, metrics, and logs.

🚀 Features

  • Automatic instrumentation of ASP.NET Core and HTTP client calls
  • OTLP export to any compatible backend (Jaeger, Tempo, Prometheus, etc.)
  • Traces, metrics, and logs correlation
  • Console exporter for local debugging
  • Minimal configuration via appsettings.json or environment variables
  • Production-ready with configurable endpoints and service names

📖 Configuration Parameters

Configuration can be provided through appsettings.json or environment variables.

Parameter Required Type Purpose Notes Example
Enable ✅ Yes Boolean Enable/disable OpenTelemetry instrumentation Set to false to completely disable telemetry true
ServiceName Optional String Name of the service for tracing Helps identify traces in your observability platform "SlimFaas"
Endpoint Conditional String (URL) OTLP exporter endpoint (gRPC) Required if Enable is true "http://localhost:4317"
EnableConsoleExporter Optional Boolean Export to console for debugging Useful for local development false
ExcludedUrls Optional string array List of URL path prefixes to exclude from tracing ["/health", "/metrics"]

Configuration Priority (default behavior):

  1. Configuration values from appsettings.json (highest priority)
  2. Environment variables OTEL_SERVICE_NAME and OTEL_EXPORTER_OTLP_ENDPOINT (fallback if configuration values are not specified)
  3. If Enable is true and no Endpoint is found in either configuration or environment variables, the OpenTelemetry default value will be used.

📦 Quick Start

appsettings.json Configuration

{
  "OpenTelemetry": {
    "Enable": true,
    "ServiceName": "SlimFaas",
    "Endpoint": "http://localhost:4317",
    "EnableConsoleExporter": false,
    "ExcludedUrls": ["/health", "/metrics", "/swagger"]
  }
}

Environment Variables

# Windows
set OpenTelemetry__Enable=true
set OpenTelemetry__ServiceName=SlimFaas
set OpenTelemetry__Endpoint=http://localhost:4317
set OpenTelemetry__EnableConsoleExporter=false
set OpenTelemetry__ExcludedUrls__0=health
set OpenTelemetry__ExcludedUrls__1=metrics

# Linux/Mac
export OpenTelemetry__Enable=true
export OpenTelemetry__ServiceName=SlimFaas
export OpenTelemetry__Endpoint=http://localhost:4317
export OpenTelemetry__EnableConsoleExporter=false
export OpenTelemetry__ExcludedUrls__0=heatlh
export OpenTelemetry__ExcludedUrls__1=metrics

🔌 What is Collected

Traces

SlimFaas automatically instruments:

  • ✅ HTTP requests via ASP.NET Core instrumentation. URLs specified in ExcludedUrls are filtered from tracing based on case-insensitive path prefix matching. For example, /health will exclude /health, /health/live, /health/ready, etc.
  • Empty or missing ExcludedUrls configuration will use the default values ["/health", "/metrics"]
  • ✅ HTTP client calls to functions and external services

Logs

  • ✅ Application logs exported via OTLP
  • Note: URL filtering does not apply to logs; all logs are collected regardless of ExcludedUrls

Metrics

Exported metrics include:

  • ✅ ASP.NET Core metrics: request duration, request count, etc.
  • ✅ HTTP client metrics: outbound request duration and count
  • Note: URL filtering does not apply to metrics; all metrics are collected regardless of ExcludedUrls

🐛 Debugging with Console Exporter

For local development and debugging, enable the console exporter:

{
  "OpenTelemetry": {
    "Enable": true,
    "ServiceName": "SlimFaas",
    "Endpoint": "http://localhost:4317",
    "EnableConsoleExporter": true,
    "ExcludedUrls": ["/health", "/metrics", "/swagger"]
  }
}

This will output telemetry data directly to the console alongside the OTLP export.

Enjoy distributed tracing with SlimFaas! 🚀