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

Question

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

Answer 1

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