https://github.com/baronfel/otel-startup-hook

A .NET CLR Startup Hook that exports OpenTelemetry metrics via the OTLP Exporter to an OpenTelemetry Collector
https://github.com/baronfel/otel-startup-hook

dotnet opentelemetry

Last synced: 29 days ago
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A .NET CLR Startup Hook that exports OpenTelemetry metrics via the OTLP Exporter to an OpenTelemetry Collector

• Host: GitHub
• URL: https://github.com/baronfel/otel-startup-hook
• Owner: baronfel
• License: mit
• Created: 2024-02-01T17:18:07.000Z (10 months ago)
• Default Branch: main
• Last Pushed: 2024-02-01T17:46:37.000Z (10 months ago)
• Last Synced: 2024-10-06T15:22:50.624Z (about 1 month ago)
• Topics: dotnet, opentelemetry
• Language: C#
• Homepage:
• Size: 10.7 KB
• Stars: 4
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# An OpenTelemetry Startup Hook for .NET

This library is a ready-to-use [.NET CLR Startup Hook](https://github.com/dotnet/runtime/blob/52e1ad3779e57c35d2416cd10d8ad7d75b2c0c8b/docs/design/features/host-startup-hook.md) that allows applications that are instrumented with [System.Diagnostic.Activity tracing](https://learn.microsoft.com/en-us/dotnet/core/diagnostics/distributed-tracing-instrumentation-walkthroughs) to

send those traces to an [OpenTelemetry Collector](https://opentelemetry.io/docs/collector/) via an [OpenTelemetry Exporter](https://opentelemetry.io/docs/languages/net/exporters/) without having to add references to the [OpenTelemetry SDK](https://opentelemetry.io/docs/languages/net/) into their applications directly.

## Getting Started

To use this hook in your application, you'll need:

* An application that already has System.Diagnostic.Activity tracing enabled

* An OpenTelemetry Collector running and ready to receive traces (for example [otel-desktop-viewer](https://github.com/CtrlSpice/otel-desktop-viewer))

* This repo cloned locally

* A .NET 8+ SDK installed

### Building the Hook

Publishing this project is all you need. The project and all of its dependencies will be combined into one output assembly (at `./bin/Release/net8.0/publish/otel-startup-hook.dll`)

```terminal

dotnet publish

```

### Using the Hook

Get the absolute path of the freshly-built DLL from the previous step, and set it as the value of the `DOTNET_STARTUP_HOOKS` environment variable.

Bash/Zsh/etc:

```bash

export DOTNET_STARTUP_HOOKS=/path/to/otel-startup-hook.dll

```

Powershell

```powershell

$env:DOTNET_STARTUP_HOOKS = "C:\path\to\otel-startup-hook.dll"

```

Then, run your application as you normally would. The hook will automatically start up and begin sending traces to the OpenTelemetry Collector.

## Configuration

### Configuring what is collected

Currently, only Traces are collected. Each 'source' you want to collect from must be set in the `OTEL_TRACE_SOURCE_NAMES` environment variable. This is a comma-separated list of source names, and these source names are usually defined in your application when you create an ActivitySource:

```csharp

using System.Diagnostics;

public static class Telemetry

{

    //...

    // Name it after the service name for your app.

    // It can come from a config file, constants file, etc.

    public static readonly ActivitySource MyActivitySource = new("myapp");

    //...

}

```

### Configuring where the traces are sent

This hook uses the [OTLP endpoint exporter](https://opentelemetry.io/docs/languages/net/exporters/#otlp-endpoint) to send traces to the OpenTelemetry Collector. This defaults to sending traces over gRPC to `http://localhost:4317`. You can configure how the OTLP exporter behaves by setting various environment variables, as described in the [OTLP Exporter Configuration](https://opentelemetry.io/docs/languages/sdk-configuration/otlp-exporter/) documentation.