FastAPI + NGINX + Docker connection refused

I'm trying to create a simple docker-compose that would launch 2 containers one for the app as seen below:

from fastapi import APIRouter

router = APIRouter()


@router.get("/")
async def root():
    return {"message": "This is a Test"}

from fastapi import FastAPI
import uvicorn as uvicorn

from routers import test


app = FastAPI()
app.include_router(test.router)


if __name__ == "__main__":
    uvicorn.run(app, host="0.0.0.0", port=8000)

The other for NGINX with the configuration:

worker_processes 1;

events {
  worker_connections 1024;
}

http {
    server {
        listen       80;

        location / {
            proxy_pass http://0.0.0.0:8000;
        }
    }
}

My docker-compose is as followed:

version: "3.7"
services:
    web:
        build: nginx
        ports:
          - "80:80"
        depends_on:
          - app
        container_name: tensor_nginx

    app:
        build: app
        ports:
          - "8000:8000"
        container_name: test

When i fire up everything starts fine and I can connect to the Swagger created by FastAPI by going 0.0.0.0:8000/docs and the endpoint returns the string defined in the code.

But if I try to connect using nginx port it says connection failed.

[error] 30#30: *5 connect() failed (111: Connection refused) while connecting to upstream, client: 172.31.0.1, server: , request: "GET / HTTP/1.1", upstream: "http://0.0.0.0:8000/", host: "127.0.0.1"

What am I missing in the configurations?

The line proxy_pass http://0.0.0.0:8000; of nginx conf does not make sense (since nginx is deployed inside a container, address 0.0.0.0 cannot be resolved), here you need to specify the full address before the end device or domain name. In your case, you can use the domain name from the docker compose file such as
proxy_pass http://app:8000 or set domain main manually

app:
	build: app
    hostname: my-fastapi-app
	ports:
	  - "8000:8000"

and

proxy_pass http://my-fastapi-app:8000;