python runtime_error ai_generated true

RuntimeError: Cannot add middleware after an application has started

ID: python/starlette-middleware-order-500

Also available as: JSON · Markdown · 中文
80%Fix Rate
86%Confidence
0Evidence
2024-11-08First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
3.x active — — —

Root Cause

add_middleware is called after the ASGI app has begun handling requests, e.g. inside a startup event or a route.

generic

中文

在 ASGI 应用开始处理请求后（例如在 startup 事件或路由中）调用了 add_middleware。

Workarounds

  1. 93% success 
    Register middleware at module level before the app starts:
app.add_middleware(GZipMiddleware)
  2. 85% success 
    Use lifespan for startup logic, not middleware registration.

Dead Ends

Common approaches that don't work:

  1. 90% fail

    Startup runs after the middleware stack is built; the error is raised.

  2. 75% fail

    The middleware is never applied, so behavior silently differs.