By fabio geraci
Hello, i must say this is my first project. Now I built a flask app, that uses a image classifier. the flask integration works fine locally, but i would like to deploy the app to a lager audience.
i followed the deployment strategy proposed on this git https://github.com/digitalocean/sample-flask.git but i get the following error:
number-reader | 12:12:52 usage: gunicorn [OPTIONS] [APP_MODULE] number-reader | 12:12:52 gunicorn: error: No application module specified.
app = Flask(__name__)
# To setup Bootstrap templates
Bootstrap(app)
# Load trained model
with open("model/classifier.pickle", "rb") as handle:
classifier = pickle.load(handle)
@app.route('/', methods=['GET', 'POST'])
def load_image():
if request.method == 'POST':
if __name__ == '__main__':
app.run(debug=True)
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Try something like this in settings->components->your component:
gunicorn --worker-tmp-dir /dev/shm app:app
The first part is something that digitalocean suggests: “”“Gunicorn crashes with PermissionError unless launched with a specific argument due to an issue with Gunicorn running in Docker. To resolve, run Gunicorn to use a different location for its temp files by passing this option to the run command: gunicorn --worker-tmp-dir /dev/shm project.wsgi”“”
But it worked for me changing the project.wsgi for app:app (it is what I use on my local machine for testing, since my app file is called app.py)
The error you’re encountering suggests that Gunicorn, the Python WSGI HTTP Server for UNIX, is not able to find your Flask application object. When you deploy a Flask app using Gunicorn, you need to specify the application object it should serve. This is usually done in the command that starts Gunicorn.
Based on your code snippet, it looks like your Flask app is defined as app in the Python file where your Flask application is located. The way you start Gunicorn must include a reference to this app object, typically in the format module:app. Here, module is the name of the Python file containing your Flask application (without the .py extension), and app is the Flask application object.
Here’s how you can resolve this issue:
-
Ensure Correct File Structure: Your Flask application should be in a Python file, let’s assume it’s named
app.py. -
Gunicorn Command: The command to start Gunicorn should reference this file and the Flask app object. If your file is named
app.pyand your Flask object isapp, the command should be:
gunicorn app:app
Make sure this command is used in your deployment process.
- Review Procfile (If using Heroku or Similar): If you’re deploying on a platform like Heroku, this command should be in your
Procfile. TheProcfileshould contain:
web: gunicorn app:app
-
Ensure app.py is Accessible: The
app.pyfile (or whatever your main file is named) should be in the root directory of your project, or the path should be correctly specified in the Gunicorn command. -
Check for Typos: Ensure there are no typos in your file names and in your Gunicorn command.
-
No Conditional
app.run(): When deploying with Gunicorn, you don’t need theif __name__ == '__main__': app.run(debug=True)block in your code. Gunicorn acts as the web server, and you won’t be running the app directly with Python. -
Adjust for Non-Standard Structures: If your Flask app object is in a different file or is named differently, adjust the Gunicorn command accordingly. For example, if the Flask app object named
myappis in a file namedmyapplication.py, the command would begunicorn myapplication:myapp.
After making these adjustments, try redeploying your application. If the problem persists, you may need to check your deployment configuration and ensure all paths and file names are correctly specified.
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