---
title: "Trace Propagation"
description: "Learn how to connect events across applications/services."
url: https://docs.sentry.io/platforms/dotnet/guides/aspnet/tracing/trace-propagation/
---

# Trace Propagation | Sentry for ASP.NET

If the overall application landscape that you want to observe with Sentry consists of more than just a single service or application, distributed tracing can add a lot of value.

## [What is Distributed Tracing?](https://docs.sentry.io/platforms/dotnet/guides/aspnet/tracing/trace-propagation.md#what-is-distributed-tracing)

In the context of tracing events across a distributed system, distributed tracing acts as a powerful debugging tool. Imagine your application as a vast network of interconnected parts. For example, your system might be spread across different servers or your application might split into different backend and frontend services, each potentially having their own technology stack.

When an error or performance issue occurs, it can be challenging to pinpoint the root cause due to the complexity of such a system. Distributed tracing helps you follow the path of an event as it travels through this intricate web, recording every step it takes. By examining these traces, you can reconstruct the sequence of events leading up to the event of interest, identify the specific components involved, and understand their interactions. This detailed visibility enables you to diagnose and resolve issues more effectively, ultimately improving the reliability and performance of your distributed system.

## [Basic Example](https://docs.sentry.io/platforms/dotnet/guides/aspnet/tracing/trace-propagation.md#basic-example)

Here's an example showing a distributed trace in Sentry:

This distributed trace shows a Vue app's `pageload` making a request to a Python backend, which then calls the `/api` endpoint of a Ruby microservice.

What happens in the background is that Sentry uses reads and further propagates two HTTP headers between your applications:

* `sentry-trace`
* `baggage`

If you run any JavaScript applications in your distributed system, make sure that those two headers are added to your CORS allowlist and won't be blocked or stripped by your proxy servers, gateways, or firewalls.

## [How to Use Distributed Tracing?](https://docs.sentry.io/platforms/dotnet/guides/aspnet/tracing/trace-propagation.md#how-to-use-distributed-tracing)

If you use the current version of our .NET SDK, distributed tracing works automatically with the following frameworks:

* ASP.NET Core
* Azure Functions Worker

When using ASP.NET (not ASP.NET Core), you have to hook into the request lifecycle in `Global.asax.cs` to propagate traces. There are two options, depending on whether you want this application to create its own transactions and spans.

### [Create Transactions and Continue the Trace (Recommended)](https://docs.sentry.io/platforms/dotnet/guides/aspnet/tracing/trace-propagation.md#create-transactions-and-continue-the-trace-recommended)

In most cases you'll want your ASP.NET application to show up in your distributed traces with its own transactions and spans. Use `StartSentryTransaction` in `Application_BeginRequest` and `FinishSentryTransaction` in `Application_EndRequest`. `StartSentryTransaction` continues any incoming trace and creates a transaction for the request.

```csharp
protected void Application_BeginRequest()
{
    Context.StartSentryTransaction();
}

protected void Application_EndRequest()
{
    Context.FinishSentryTransaction();
}
```

### [Continue the Trace Without Creating Transactions](https://docs.sentry.io/platforms/dotnet/guides/aspnet/tracing/trace-propagation.md#continue-the-trace-without-creating-transactions)

If you only want to propagate an incoming trace to downstream services (for example, a database or another API) without your ASP.NET application creating any transactions or spans of its own, use `StartOrContinueTrace` instead:

```csharp
protected void Application_BeginRequest()
{
    Context.StartOrContinueTrace();
}
```

Use either `StartSentryTransaction` or `StartOrContinueTrace`, not both. `StartOrContinueTrace` only propagates the trace and does not create a transaction, so if you replace `StartSentryTransaction` with it, your ASP.NET application will stop sending transactions to Sentry. Since `StartSentryTransaction` already continues the incoming trace, most applications should use that method.

Remember that in order to propagate trace information through your whole distributed system, you have to use Sentry in all of the involved services and applications. Take a look at the respective SDK documentation to learn how distributed tracing can be enabled for each platform.

## Pages in this section

- [Custom Instrumentation](https://docs.sentry.io/platforms/dotnet/guides/aspnet/tracing/trace-propagation/custom-instrumentation.md)
- [Dealing with CORS Issues](https://docs.sentry.io/platforms/dotnet/guides/aspnet/tracing/trace-propagation/dealing-with-cors-issues.md)