App Runner fails to complete health check for FastAPI app

Question

I'm attempting to deploy a FastAPI app to App Runner via a deployed Docker image on ECR. It works fine when running a local Docker container (on 0.0.0.0:8080), but fails to deploy on App Runner because the health check fails.

Here's the associated Dockerfile:

FROM python:3.11-bullseye

# Turns off buffering for easier container logging
ENV PYTHONUNBUFFERED=1

# Expose port you want your app on
ENV PORT=8080

EXPOSE ${PORT}

RUN apt update && apt install ffmpeg unzip -y && apt clean

ENV APP_HOME /app
WORKDIR $APP_HOME

# Install production dependencies.
COPY requirements.txt .
RUN pip install -r requirements.txt --no-cache-dir && pip install hypercorn --no-cache-dir
RUN pip install "pydantic[email]" pydantic_settings gdown

RUN gdown --fuzzy "<redacted>"

RUN unzip tokenizer_model.zip

COPY . .

RUN adduser -u 5678 --disabled-password --gecos "" appuser && chown -R appuser /app
USER appuser

CMD exec hypercorn --bind :$PORT --workers 2 app:app

Additionally, I've added a /health endpoint that returns a 200 OK message. I've also adjusted the configuration settings on App Runner accordingly.

I did add some logging messages for when the app starts, but I can't see anything on the App Runner console. Here are the event logs:

06-13-2024 08:35:27 AM [AppRunner] Successfully pulled your application image from ECR.
06-13-2024 08:35:37 AM [AppRunner] Provisioning instances and deploying image for publicly accessible service.
06-13-2024 08:35:46 AM [AppRunner] Performing health check on protocol `HTTP` [Path: '/health'], [Port: '8080'].
06-13-2024 08:42:00 AM [AppRunner] Health check failed on protocol `HTTP`[Path: '/health'], [Port: '8080']. Check your configured port number. For more information, see the application logs.
06-13-2024 08:42:13 AM [AppRunner] Deployment with ID : abe5baee271644b28f07eda47f100583 failed. Failure reason : Health check failed.

Would really appreciate some assistance here.