Why is Flask application not creating any logs when hosted by Gunicorn?

This approach works for me: Import the Python logging module and add gunicorn’s error handlers to it. Then your logger will log into the gunicorn error log file:

import logging

app = Flask(__name__)

gunicorn_error_logger = logging.getLogger('gunicorn.error')
app.logger.handlers.extend(gunicorn_error_logger.handlers)
app.logger.setLevel(logging.DEBUG)
app.logger.debug('this will show in the log')

My Gunicorn startup script is configured to output log entries to a file like so:

gunicorn main:app \
    --workers 4 \
    --bind 0.0.0.0:9000 \
    --log-file /app/logs/gunicorn.log \
    --log-level DEBUG \
    --reload