---
title: "Custom Trace Propagation"
url: https://docs.sentry.io/platforms/python/tracing/distributed-tracing/custom-trace-propagation/
---

# Custom Trace Propagation | Sentry for Python

Distributed tracing works out of the box for [supported frameworks](https://docs.sentry.io/platforms/python/distributed-tracing.md#how-to-use-distributed-tracing) and when [tracing](https://docs.sentry.io/platforms/python/tracing.md) is enabled. If you're using an unsupported framework or don't want to turn on tracing, you can set up custom instrumentation for distributed tracing.

This page describes how to manually propagate trace information into and out of your Python application. All you have to do is to make sure your application extracts incoming headers and to set those headers again when making an outgoing request within your application.

## [1. Extract Incoming Tracing Information](https://docs.sentry.io/platforms/python/tracing/distributed-tracing/custom-trace-propagation.md#1-extract-incoming-tracing-information)

Incoming tracing information has to be extracted and stored in memory for later use. Sentry provides the `continue_trace()` function to help you with this. Incoming tracing information can come from different places:

* In a web environment, it's sent with HTTP headers, for example, by another Sentry SDK used in your frontend project.
* In a job queue, like Celery, it can be retrieved from meta or header variables.
* You also can pick up tracing information from environment variables.

Here's an example of how to extract and store incoming tracing information using `continue_trace()`:

```python
import sentry_sdk
from my_project import get_incoming_headers_as_dict

headers = get_incoming_headers_as_dict()

transaction = sentry_sdk.continue_trace(headers)
with sentry_sdk.start_transaction(transaction):
    ...
```

In this example, `get_incoming_headers_as_dict()` returns a dictionary that contains tracing information from HTTP headers, environment variables, or any other mechanism your project uses to communicate with the outside world.

Sentry's `continue_trace()` function will extract the given headers, try to find the `sentry-trace` and `baggage` headers, and store them in memory for later use.

`continue_trace()` returns a transaction, but does not start it. To start the transaction, use `start_transaction()`.

## [2. Inject Tracing Information to Outgoing Requests](https://docs.sentry.io/platforms/python/tracing/distributed-tracing/custom-trace-propagation.md#2-inject-tracing-information-to-outgoing-requests)

For distributed tracing to work, the two headers `sentry-trace` and `baggage`, must be added to outgoing requests. If you pregenerate HTML on the server-side, you might want to take a look at [Inject Tracing Information into Rendered HTML](https://docs.sentry.io/platforms/python/tracing/distributed-tracing/custom-trace-propagation.md#inject-tracing-information-into-rendered-html), which describes how to pass on tracing information through HTML meta tags.

### [Inject Tracing Information Into HTTP Requests](https://docs.sentry.io/platforms/python/tracing/distributed-tracing/custom-trace-propagation.md#inject-tracing-information-into-http-requests)

If you are sending outgoing HTTP requests with [Requests](https://requests.readthedocs.io/en/latest/), [AIOHTTP](https://docs.aiohttp.org/en/stable/), the low level [http.client](https://docs.python.org/3/library/http.client.html), or [httplib](https://docs.python.org/2/library/httplib.html) on Python 2, this tracing information is automatically added to outgoing requests.

If you're using none of the above, you can generate this tracing information with the Sentry SDK's `get_traceparent()` and `get_baggage()` functions. Here's an example:

```python
import sentry_sdk
from my_project import make_an_outgoing_request

headers = {}
headers["sentry-trace"] = sentry_sdk.get_traceparent()
headers["baggage"] = sentry_sdk.get_baggage()

make_an_outgoing_request(to="https://example.com", headers=headers)
```

In this example, tracing information is propagated to the project running at `https://example.com`. If this project uses the Sentry Python SDK, it will extract and save the tracing information for later use.

The two services are now connected with your custom distributed tracing implementation.

### [Inject Tracing Information into Rendered HTML](https://docs.sentry.io/platforms/python/tracing/distributed-tracing/custom-trace-propagation.md#inject-tracing-information-into-rendered-html)

To propagate tracing information into JavaScript running in rendered HTML, you have to inject HTML `meta` tags for `sentry-trace` and `baggage` data into your rendered HTML. Here's an example:

```python
import sentry_sdk
from my_project import render

meta = ""
meta += '<meta name="sentry-trace" content="%s">' % sentry_sdk.get_traceparent()
meta += '<meta name="baggage" content="%s">' % sentry_sdk.get_baggage()

html = """
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        {additional_meta}
    </head>
    <body>
        <p>This is a website.</p>
    </body>
</html>
""".format(additional_meta=meta)

render(html)
```

## [Verification](https://docs.sentry.io/platforms/python/tracing/distributed-tracing/custom-trace-propagation.md#verification)

If you make outgoing requests from your project to other services, check if the headers `sentry-trace` and `baggage` are present in the request. If so, distributed tracing is working.