Mounting on FastAPI deployed on Posit Connect redirects to 127.0.0.1

[tonisama]

Describe the bug
I've mounted my Chainlit app as a FastAPI sub-application as outlined here https://docs.chainlit.io/integrations/fastapi. I've tested this locally and it works as expected.

I tried to deploy the app as a FastAPI on Posit Connect, and when navigating to /chainlit, I get redirected to 127.0.0.1. The /docs and /app do work as expected which means FastAPI is correctly set up.

Tried adding environmental variables with no effect:
CHAINLIT_HEADLESS = true
CHAINLIT_NO_ONBOARDING = true
CHAINLIT_PUBLIC_PATH = '/chainlit'

To Reproduce
Steps to reproduce the behavior:

1. Go to 'https://docs.chainlit.io/integrations/fastapi'
2. Copy all code into the appropriate files in a directory
3. Deploy the app using the command line: 'rsconnect deploy fastapi --entrypoint main:app --server [your_server_URL] --api-key [your_API_key] ./
4. Attempt to navigate to your deployed app at: '[your_app_url]/chainlit'

Expected behavior
Expect to see the app load. Instead, redirected to 127.0.0.1/[rest_of_URL]/chainlit and a 'page not found' error.

Note if mounting locally using uvicorn, the app loads fine.

[willydouhard]

When started locally on the sub path is it working? What version of Chainlit are you using?

[tonisama]

When started locally on the sub path is it working? What version of Chainlit are you using?

Yes, it works locally, either by using "chainlit run" or by running a FastAPI with uvicorn web server and navigating to "localhost/chainlit" I'm using 1.3.2, however I just upgraded to 2.0.0 and got the same issue.

[tonisama]

Posit Support replied back saying "Chainlit doesn't appear to correctly handle running behind a proxy with a non-empty root path." I'm not sure I necessarily buy this.