__call__() missing 1 required positional argument: 'send' FastAPI on App Engine

user_14109203 0
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When trying to host an API on App Engine, the following error keeps coming up. The program used to run on Flask which was working but very slow.

Error:

"Traceback (most recent call last):
  File "/env/lib/python3.7/site-packages/gunicorn/workers/sync.py", line 134, in handle
    self.handle_request(listener, req, client, addr)
  File "/env/lib/python3.7/site-packages/gunicorn/workers/sync.py", line 175, in handle_request
    respiter = self.wsgi(environ, resp.start_response)
TypeError: __call__() missing 1 required positional argument: 'send'
"

Docker File:

FROM gcr.io/google_appengine/python

RUN apt-get update && apt-get install -y ffmpeg

# Create a virtualenv for dependencies. This isolates these packages from
# system-level packages.

RUN virtualenv /env -p python3.7

# Setting these environment variables are the same as running
# source /env/bin/activate.

ENV VIRTUAL_ENV /env
ENV PATH /env/bin:$PATH

ADD requirements.txt /app/requirements.txt
RUN pip install -r /app/requirements.txt

# Add the application source code.

ADD . /app

CMD gunicorn -w 4 -k uvicorn.workers.UvicornWorker main:app

app.yaml

runtime: custom
env: flex
entrypoint: gunicorn -w 4 -k uvicorn.workers.UvicornWorker main:app
service: encoder

runtime_config:
  python_version: 3

handlers:

- url: /.*
  script: auto
gunicorn fastapi google-cloud-platform google-app-engine python
4 Answers

As Dustin said I found out that worker class need to be changed. Try the below one.

gunicorn -k uvicorn.workers.UvicornWorker main:app

Found this on github issues

user_137560790

App Engine requires your main.py file to declare an app variable which corresponds to a WSGI Application.

Since FastAPI is an asynchronous web framework, it is not compatible with WSGI (which is synchronous).

Your best option would be to use a service like Cloud Run, which would allow you to define your own runtime and use an asynchronous HTTP server compatible with FastAPI.

user_3280360

I ran into the same issue when I want to deploy a FastAPI app to Heroku. Indeed, you can't use uvicorn (which is the ASGI framework that FastAPI is using) with Heroku that uses gunicorn.

However, by adding a uvicorn worker to gunicorn then it works!:

gunicorn api:app --bind 0.0.0.0:$PORT --worker-class uvicorn.workers.UvicornWorker

user_117281280

I solved it by putting python main.py as the build command and setting my uvicorn command in the main.py as uvicorn.run("main:app", host="0.0.0.0", port=8080)

user_105591720
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