Fastapi: [BUG] Unable to correctly reverse proxy FastAPI

[ybizeul]

Describe the bug

When using FastAPI behind a proxy that adds path elements like /api/1.0/, there is no way to correctly display the swagger

To Reproduce

1. Configure a reverse proxy to send /api/1.0/ to your FastAPI server
2. access swagger for the API
3. Observe that all your objects are prefixed with /api/1.0

See screenshot

Expected behavior

/api/1.0 should not be part of API documentation.

OpenAPI documents this here

There should be a way to configure Server URL to /api/1.0 like indicated in the examples.

Screenshots

Environment

• OS: alpine docker image
• FastAPI Version 0.54.1
• Python version 3.7.3

Additional context

Using Traefik as reverse proxy. Traefik like other proxies, has the ability to either :
Pass the request as-is with /api/1.0/, or strip the part from the URL and put it in the X-Forwarded-Prefix header. Maybe that could be used as the server URL for Swagger.

[esomir]

You can use openapi_prefix (https://fastapi.tiangolo.com/advanced/sub-applications-proxy/) but that's not really viable when the application doesn't know under which prefix it's running from.

Ideally, it should be resolved dynamically based on the X-Forwarded-Prefix. We are using Traefik and having the same problem. We are having a PathPrefix on our route, and using the StripPrefix middleware, which will strip the prefix, and pass it to the X-Forwarded-Prefix header.

[ybizeul]

That's exactly my situation. Traefik passes all the information but they are not leveraged by fastapi. I switched to Connexion since then

[sm-Fifteen]

Related to #829. @ybizeul raises a good point that the application's root path should probably be included in a server object in the generated OpenAPI documentation and omitted from the routes in the API.

FastAPI's current behavior (not specifying a servers array) falls back to the specification's default, which is this:

If the servers property is not provided, or is an empty array, the default value would be a Server Object with a url value of /.

So equivalent to:

servers:
  - url: '/'

[tiangolo]

Passing the root_path was addressed in https://github.com/tiangolo/fastapi/pull/1199 :rocket:

Available in FastAPI 0.56.0.

Here are new docs on running FastAPI Behind a Proxy with a Traefik example.

It could be passed to Uvicorn as:

$ uvicorn app:main --root-path=/api/1.0

---

About reading the X-Forwarded-Prefix, that would be a feature request to Uvicorn, to read it when using --proxy-headers and set the root_path in the ASGI scope with it.

If it is implemented there, it will be automatically supported here.

[ybizeul]

From what I see in the documentation you point me to, it's not fixed at all and /api/blah is still part of the path for every path

[tiangolo]

Ah, you are right, I didn't interpret your original issue description correctly.

You expected it to _not_ contain the prefix and still work.

I have to investigate how the servers would interact with the rest.

[tiangolo]

This was fixed/implemented by @rkbeatss in https://github.com/tiangolo/fastapi/pull/1596. :tada:

Available in FastAPI version 0.59.0. :rocket:

New docs here: https://fastapi.tiangolo.com/advanced/behind-a-proxy/#additional-servers

[github-actions[bot]]

Assuming the original issue was solved, it will be automatically closed now. But feel free to add more comments or create new issues.