Merge Traces from 2 separate applications?

[bsonnek]

Is it possible to have 2 separate apps write to the same trace or session_id?

I have a frontend python streamlit chatbot app and a backend python RAG orchestrator app, both apps are running in separate containers. They both connect to the same Langfuse project. I was wondering if it's possible to merge both traces that are generated into a single trace in langfuse?

Thanks in advance!

[dosubot[bot]]

Hello @bsonnek! I'm here to help you with any bugs, questions, or contributions. Let's see how we can tackle this challenge together!

Langfuse allows you to merge traces from different applications by using the same sessionId for traces that you want to group together. By assigning the same sessionId to traces from both your frontend and backend applications, Langfuse will group them into a single session, effectively merging them ^[1][2].

You can achieve this by updating the current trace with a consistent sessionId in both applications. Here's an example using the @observe() decorator in Python:

from langfuse.decorators import langfuse_context, observe

@observe()
def your_function():
    langfuse_context.update_current_trace(
        session_id="your-shared-session-id"
    )

Ensure that both your frontend and backend applications use the same sessionId when creating or updating traces. This will allow Langfuse to merge them into a single session.

To continue talking to Dosu, mention @dosu.

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[marcklingen]

Yes, all integrations support using your own traceIds. Thereby the observations will be merged.

Alternatively you can use sessions as outlined by dosu but this will result in two separate traces.

[bsonnek]

Hi Marck - thanks for the quick reply. I do see 2 separate traceIds when I use the same session_id between both apps.

How do I use my own traceIds? I can't seem to find how to do that?

[marcklingen]

I do see 2 separate traceIds when I use the same session_id between both apps.

That's the expected/desired behavior. See docs: https://langfuse.com/docs/tracing-features/sessions

Which integration do you use? They should all allow to configure your own traceId

[bsonnek]

I sorta figured this was expected/desired behavior. I just wanted to make sure I wasn't missing something. I don't think I need to manage my own tradeIds.

"Which integration do I use? = Python - Is that what you mean by integration?

This is working for me now. I pass the UID between both apps in the API call. And I do see 2 separate traces.

generated_uid = str(uuid.uuid4())
langfuse_context.update_current_trace(
        name="Ask AI",
        metadata={"User_Question": user_question},
        session_id = generated_uid
    )

Thanks for the quick response. I just wanted to make sure I wasn't missing anything.