To run an app that uses ASGI (minimal basic setup, adjust and expand as needed):

Go to https://my.opalstack.com/apps/.
Create a new "Nginx Proxy Port" application and make a note of the app name and port assignment.
Log in to a SSH session as the app's shell user.

Execute the following commands to create a new Python environment using uvicorn as the ASGI server.

cd ~/apps/name_of_app
python3.11 -m venv env
source env/bin/activate
pip install gunicorn uvicorn

Upload your project to the app directory, the rest of this example will use myproject as the project name.
Install your project dependencies.

Create a file ~/apps/name_of_app/start with the following contents:

#!/bin/bash

# replace appname with your app name
APP=name_of_app

APPDIR=$HOME/apps/$APP

# set PYTHONPATH to your top level project directory, modify as needed for your project:
PYTHONPATH=$APPDIR/myproject

# set HANDLER to your ASGI handler, eg for `myproject/asgi.py` use:
HANDLER=myproject.asgi

# set PORT to your app's port:
PORT=NNNNN

STARTCMD="$APPDIR/env/bin/gunicorn -D -b 127.0.0.1:$PORT -w 4 -k uvicorn.workers.UvicornWorker $HANDLER:application"

(pgrep -f "$STARTCMD" > /dev/null && echo "$APP already running.") || (PYTHONPATH=$PYTHONPATH $STARTCMD && echo "started $APP.")

Create a file ~/apps/name_of_app/stop with the following contents:

#!/bin/bash

# replace appname with your app name
APP=name_of_app

APPDIR=$HOME/apps/$APP

# set HANDLER to your ASGI handler, eg for `myproject/asgi.py` use:
HANDLER=myproject.asgi

# set PORT to your app's port:
PORT=NNNNN

STARTCMD="$APPDIR/env/bin/gunicorn -D -b 127.0.0.1:$PORT -w 4 -k uvicorn.workers.UvicornWorker $HANDLER:application"

pgrep -f "$STARTCMD" > /dev/null && pkill -f "$STARTCMD" && echo "stopped $APP." || echo "$APP not running."

Run the following commands to make your start and stop scripts executable:

chmod 700 ~/apps/name_of_app/start
chmod 700 ~/apps/name_of_app/stop

Run ~/apps/name_of_app/start to start the app.