Did you configure CORS in your fastapi backend?
https://fastapi.tiangolo.com/tutorial/cors/#use-corsmiddleware

In your case it'd be similar to:

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware

origins = [
    "https://emails.felipe.fun",
]

app.add_middleware(
    CORSMiddleware,
    allow_origins=origins,
)

I did the 'cors' configuration and I still have the same problem

my original cors code

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware

def setup_cors(app: FastAPI):
    origins = [
        "https://emails.felipe.fun"
    ]

    app.add_middleware(
        CORSMiddleware,
        allow_origins=origins,
        allow_credentials=True,
        allow_methods=["*"],
        allow_headers=["*"],
    )

my repo: https://github.com/FelipeRos19/BackendDesafioAutoU

I removed my settings and left only the one you sent and I still have the same problem, I just need to make it work even if it is not safe

Your config looks fine 🤔

FROM python:3.12-slim

WORKDIR /app

COPY requirements.txt .

RUN pip install --no-cache-dir -r requirements.txt

COPY . .

EXPOSE 8000

CMD ["gunicorn", "-k", "uvicorn.workers.UvicornWorker", "main:app", "--bind", "0.0.0.0:8000", "--workers", "4"]

my dockerfile

PS C:\Users\felip> curl.exe -i -X OPTIONS https://back-email.felipe.fun/text
HTTP/1.1 502 Bad Gateway
Content-Length: 109
Content-Type: application/json
Server: railway-edge
X-Railway-Edge: railway/us-east4-eqdc4a
X-Railway-Fallback: true
X-Railway-Request-Id: PZaTRNFeRYaLYKqNwoOzXw
Date: Fri, 03 Oct 2025 00:03:37 GMT

{"status":"error","code":502,"message":"Application failed to respond","request_id":"PZaTRNFeRYaLYKqNwoOzXw"}
PS C:\Users\felip>

when I run a 'curl' I get this other problem.

Let’s try a couple things:

1. Did you put the domain to listen to port 8000? You could also put ENV var PORT with 8000

2. Unless you opted for the IPv4 feature flag, make your app listen to ipv6

    --bind "[::]:8000" \

I set it to port 8000 in the domain and created a variable PORT = 8000, now I will try to point it to IPV6

Do you have a separate frontend for this project making those requests?

yes I have a separate front end, this is the link: https://github.com/FelipeRos19/FrontendDesafioAutoU

I tested this configuration and it didn't work, I'm checking gunicorn

change https://back-email.felipe.fun/text to https://back-email.felipe.fun/text/

I've had that issue before with FastApi and a vue frontend

I did the test and I still have the same error.
I'm trying to modify the backend dockerfile

at cloudflare I'm only keeping DNS

uvicorn app.main:app --host :: --port ${PORT:-8000} --workers ${WORKERS:-3} --log-level info --proxy-headers

I use this to run my fastapi projects

in your case would be without the app.

Only main:app

You can use proxy with cloudflare, just make sure to have it in full

I'll test this now and get back to you.

not full strict, that won't work

it was already in this mode, so I don't think the problem is with cloudflare, I will test the railway domain directly

I think you are getting an error deploying the backend, because the url is not working tho

if you visit your backend url with /docs, you get a 502

I'm using https://www.nltk.org/ for some parts of the system, I'll add the files to the dockerfile to avoid downloading at startup

What do you get in logs when you visit that url?

my first time using fastapi, this project is a technical challenge and definitely not my best performance haha

don't worry, it happens

Let me give you a full dockerfile to try out

FROM python:3.12

WORKDIR /app
COPY . .
RUN pip install -r requirements.txt

CMD uvicorn app.main:app --host 0.0.0.0 --port ${PORT:-8000} --log-level info --proxy-headers

Try this one

without the app.main, only main:app

in your service settings, does it says dockerfile? You can also try removing the dockerfile and using Railpack

Now it is working, check at https://back-email.felipe.fun/docs

I tested a small modification and now the system works, but I have another problem to solve, haha.

Mixed Content: The page at 'https://emails.felipe.fun/' was loaded over HTTPS, but requested an insecure resource 'http://back-email.felipe.fun/text'. This request has been blocked; the content must be served over HTTPS.

I appreciate all your effort in helping me, you don't know how much of a difference you made in my day and in resolving the original problem

No problem! Let me see that one

Are you using cloudflare only dns? or did you change it to proxied

and using in full mode

Try removing the Dockerfile from your frontend and use it with railpack

Honestly I haven't deployed a single file, so idk if that could be the problem

I still have the same problem, I'll change the URLs to railway standard just to test and I'll get back to you

I tested some things but couldn't solve it, and within Insomnia I can only execute requests to the backend with https, so it's strange that it doesn't identify this

Try removing the / that we added before to text in the frontend, just to check

Also you could try using cloudflare in proxied, and enable the always https config

Let me see what is the config actually called

Ok, this is the option in cloudflare

and in that same page, is this one

ITS WORKSSSSSSS

Nice! Great job haha

Did cloudflare solved it, or was the url?

I changed the cloudflare configuration as you sent, and changed it to proxy mode

Excellent!

Thank you so much for your help, you just saved my life!

No worries, happy to help

I use fastapi every day, so I've faced many issues haha

I imagine haha, my experience developing was cool but DevOps was never my thing

Now I need to run to record an explanation video, thank you very much for everything! I think there's a reward for the help, it's definitely yours haha, have a great night!

Have a great night as well! If you have any future issues with fastapi, you can tag me and I'll be happy to help