Transaction name comes out wrong in Starlette integration

[gthb]

How do you use Sentry?

Sentry Saas (sentry.io)

Version

2.27.0

Steps to Reproduce

1. In my existing app (using Starlette 0.41.3) I enabled Sentry tracing by passing a traces_sampler function in the init call (see below)
2. I passed starlette.StarletteIntegration(transaction_style="endpoint") in the integrations list to work around the problem that with the default "url" style, all transactions were showing up with the name <unlabeled transaction> instead of a Starlette route binding like GET /status like I was hoping. So instead I get grid.routes.status.StatusEndpoint.get which is the name of the get method in our routing class, and I can live with that ...
3. ... but then I made the traces_sampler function filter out that name (see function below) because it's just a Kubernetes health check endpoint ... but that didn't work, I still got status transactions ... so to troubleshot that I logged sampling_context["transaction_context"]["name"] and that turns out to be the raw URL, http://123.45.6.78:5001/status

def traces_sampler(sampling_context: SamplingContext):
    if sampling_context["parent_sampled"] is not None:
        return sampling_context["parent_sampled"]

    if sampling_context["transaction_context"]["name"] == "grid.routes.status.StatusEndpoint.get":
        return 0

    return traces_sample_rate

sentry_sdk.init(
    dsn=self._config.sentry_dsn,
    integrations=[starlette.StarletteIntegration(transaction_style="endpoint"), sentry_logging],
    release=self._config.app_version,
    environment=self._config.release_stage,
    before_send=self._before_send,
    transport=custom_transport,
    traces_sampler=traces_sampler,
)

Expected Result

1. with the default transaction_style="url" I expected to get transactions named after the route paths automatically by the Starlette integration
2. once I switched to transaction_style="endpoint" and saw distinct transaction names appear in Sentry, I expected to be able to filter by those transaction names in the transaction context passed to the traces_sampler function

Actual Result

1. with the default transaction_style="url", the actual transaction names appearing in traces in Sentry are all <unlabeled transaction>
2. after I switched to transaction_style="endpoint", the actual transaction context passed to the traces_sampler function contains "name" which is the full URL (including the pod IP address in my Kubernetes cluster so it's going to vary in ways that are not useful to make transaction names vary by)

[szokeasaurusrex]

Hi @gthb – It looks like your issue is describing two separate problems; I am going to address each of them separately.

1. Getting <unlabeled transaction> with transaction_style="url"

I tried to reproduce this behavior with a simple Starlette application using Python SDK version 2.27.0 and Starlette 0.43.1, the same versions that you were using. However, I was getting the correct transaction names containing the URL paths.

Could you please provide a full reproduction that I can run locally to reproduce the <unlabeled transaction> behavior? And, could you also tell me what version of Python you are using, and on which operating system?

This additional information would be extremely helpful.

2. Unexpected transaction name in traces_sampler with transaction_style="endpoint"

The reason you are getting a different transaction name from what you expect in the traces_sampler is because the traces_sampler runs very early in the lifecycle of the transaction. For the Starlette integration, it appears that the transaction name does not get properly set until after the traces_sampler is called.

I am not sure whether it would be possible to change this behavior since traces_sampler needs to be called early on so we know whether we need to instrument the transaction. In any case, you can easily work around this problem by using before_send_transaction for filtering instead of using traces_sampler. Your updated setup would look like the following:

import sentry_sdk
from sentry_sdk.types import Event, Hint

def before_send_transaction(event: Event, _: Hint):
    if event["transaction"] == "grid.routes.status.StatusEndpoint.get":
        return None

    return event

sentry_sdk.init(
    dsn=self._config.sentry_dsn,
    integrations=[starlette.StarletteIntegration(transaction_style="endpoint"), sentry_logging],
    before_send_transaction=before_send_transaction,
    # now that we got rid of filtering in traces_sampler, the custom traces_sampler
    # is no longer needed, since it is equivalent to setting the traces_sample_rate
    # directly
    traces_sample_rate=traces_sample_rate,
    ...
)

---

Hope that information helps, please let me know if we can help any further.

[gthb]

Could you please provide a full reproduction that I can run locally to reproduce the <unlabeled transaction> behavior?

👍 — might take a little doing, as this is a big app in production. I'll post back when I have it.

And, could you also tell me what version of Python you are using, and on which operating system?

Python 3.11.2, running in pods on an EKS node running Amazon Linux 2. Kernel version (from uname -a):
5.10.228-219.884.amzn2.x86_64 #1 SMP Wed Oct 23 17:17:00 UTC 2024 x86_64 GNU/Linux
Kubelet version: v1.31.2-eks-94953ac.