root_path does not suported

[dandaniel5]

Title: Static files and admin panel assets not loading correctly behind a proxy with root_path in FastAPI

Description:

I’m running a FastAPI application behind a reverse proxy (Nginx) and have configured root_path in the FastAPI app as described in the official documentation:
https://fastapi.tiangolo.com/advanced/behind-a-proxy/

However, static files (e.g., CSS, JS) and possibly other paths are not resolving correctly.

I’m using starlette-admin, and the admin panel attempts to load assets using paths like:
<link rel="stylesheet" href="{{ url_for(__name__ ~ ':statics', path='css/tabler.min.css') }}">

My FastAPI setup:

app = FastAPI(
    version="0.0.1",
    prefix="/api/",
    root_path="/api/",
    root_path_in_servers=False,
    lifespan=lifespan 
           )

admin = Admin(title = 'Code.❤️ Admin',
                templates_dir="admin_templates/templates",
                statics_dir="admin_templates/statics",
                auth_provider=MyAuthProvider(),
              )

These static paths return 404 errors. I’ve tried the following without success:
• Serving static files manually via FastAPI routes
• Setting up separate static file routing in Nginx
• Confirming that root_path correctly prepends /api to URLs
• Rewriting asset paths using Nginx and directly injecting correct URLs

Despite all of this, the admin panel fails to load any static assets and cannot function beyond the initial page. I cannot navigate to sub-pages, and CSS/JS files do not load.

Example errors:
INFO: 185.215.54.133:0 - "GET /admin/users/list HTTP/1.0" 404 Not Found INFO: 185.215.54.133:0 - "GET /admin/statics/css/tabler.min.css HTTP/1.0" 404 Not Found INFO: 185.215.54.133:0 - "GET /admin/statics/css/fontawesome.min.css HTTP/1.0" 404 Not Found INFO: 185.215.54.133:0 - "GET /admin/statics/js/vendor/jquery.min.js HTTP/1.0" 404 Not Found INFO: 185.215.54.133:0 - "GET /admin/statics/js/vendor/js.cookie.min.js HTTP/1.0" 404 Not Found INFO: 185.215.54.133:0 - "GET /admin/statics/js/vendor/tabler.min.js HTTP/1.0" 404 Not Found

Additionally, without setting root_path, Swagger UI does not work behind a proxy — which is already a critical issue on its own.

[dandaniel5]

This is 1000% a bug. I work with this admin panel full time for a few years — I know it well. It's far from perfect. I use it in production with static files that I personally modified so they work with HTTPS.

I mean, in most situations I prefer to fix things locally by modifying your code. But now I have no clue what exactly to modify.

Can you give me a hint on how to fix this locally? For example, by changing base.html or something like that? That would be great — I can't wait for the next release, I need it to work yesterday.

[YuriiMotov]

As a workaround you can try configuring your proxy not to strip prefix from the path.
Paths passed to the app should include root path prefix:
/api/admin/statics/css/tabler.min.css instead of /admin/statics/css/tabler.min.css

You can read my attempt to break down this issue here: #2931

[dandaniel5]

Shoutout to @YuriiMotov !😄
In the end, I created a separate route for the admin like this:
location /admin/ { proxy_pass http://api_upstream; }
But actually, that was already in place before.

What I changed was the uvicorn startup command:
uvicorn main:app *** --forwarded-allow-ips='*' --proxy-headers --root-path /api
As Yury mentioned, if you pass --root-path to Uvicorn and not to FastAPI directly, then this path actually gets passed correctly to FastAPI, and as a result, the admin panel works properly, and the path stays correct — Swagger keeps working.

So here’s my final proxy config:
`
location /admin/ {
proxy_pass http://api_dev_upstream;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
}

location /api/ {
rewrite ^/api(/.*)$ $1 break;
proxy_pass http://api_dev_upstream;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
}

app = FastAPI(
title="kaatai API",
version="0.0.1",
# prefix="/api/",
# root_path="/api/",
root_path_in_servers=False,
lifespan=lifespan
)

admin = Admin(title = 'Code.❤️ Admin',
templates_dir="admin_templates/templates",
statics_dir="admin_templates/statics",
auth_provider=MyAuthProvider(),
)
`