Dapr FastAPI Extension

1.17.4 verified Fri May 01 auth: no python

The Dapr FastAPI extension integrates Dapr's pub/sub, actors, and bindings with FastAPI applications. Version 1.17.4 supports Python >=3.10, released on 2025-09-12. Release cadence is approximately monthly.

pip install dapr-ext-fastapi

Common errors

error dapr.exceptions.DaprInternalError: Actor not found ↓

cause Actor class not registered with DaprApp.

fix

Add dapr_app.register_actor(YourActorClass) after actor definition.

error ImportError: cannot import name 'DaprApp' from 'dapr.fastapi' ↓

cause Incorrect import path; the module is dapr.ext.fastapi.

fix

Use from dapr.ext.fastapi import DaprApp

error RuntimeError: DaprApp has already been initialized ↓

cause Calling dapr_app.init() or re-initializing with a second FastAPI app.

fix

Only pass the FastAPI app once in the constructor: DaprApp(app).

Warnings

breaking In v1.3.0, the subscription decorator changed from @dapr_app.subscribe to @app.post with DaprPubSubMiddleware. Old decorator no longer works. ↓

fix Use FastAPI routes with DaprPubSubMiddleware for pub/sub.

deprecated dapr_app.init() is deprecated in favor of initializing DaprApp with the FastAPI app directly. ↓

fix Use DaprApp(app) instead of DaprApp() and then dapr_app.init(app).

gotcha When using Dapr actors, ensure the actor class is registered with @actor decorator and dapr_app.register_actor is called. Missing registration results in 'Actor not found' errors. ↓

fix Call dapr_app.register_actor(MyActor) after actor definition.

Imports

DaprApp

wrong

from dapr.fastapi import DaprApp

correct

from dapr.ext.fastapi import DaprApp

Old import path changed in dapr-ext-fastapi v1.0

Quickstart

Minimal FastAPI app with Dapr extension

from fastapi import FastAPI
from dapr.ext.fastapi import DaprApp

app = FastAPI()
dapr_app = DaprApp(app)

@app.get('/')
def read_root():
    return {'message': 'Hello Dapr'}