Serving Static Files from FastAPI Frontends via CDN

Vercel has introduced a feature that promotes the frontend and static files (app.frontend() or StaticFiles) of FastAPI applications to the CDN at build time for serving. Requests to these paths are now handled directly by the CDN without invoking a Vercel Function.

Routing Priority and Exception Handling

Since FastAPI evaluates routes in the order they are declared, routes declared before a StaticFiles mount take precedence over CDN files for that path. This priority is maintained.

The original source directory remains in the function bundle so the app can read it at runtime, but setting tool.vercel.fastapi.static.exclude = true in pyproject.toml allows excluding it and serving it exclusively from the CDN.

Dependency and Middleware Handling

The CDN cannot perform dependency checks, so frontends protected by dependencies remain in the function. Static files behind middleware also remain in the function. Setting tool.vercel.fastapi.static.cdn = true overrides this behavior and always promotes them to the CDN, while setting it to false completely disables CDN usage.