Deploy a Flask App

You can find the step-by-step deployment guide here.

Application Build

Hostman uses the following environment when building a Flask application:

• Python 3.10, 3.11, 3.12, 3.13, or 3.14
• pip
• gunicorn
• System libraries for working with PostgreSQL and MySQL

Hostman will execute the following commands during the build:

apt install -y python3 python3-pip gunicorn python3-psycopg2 libpq-dev python-dev default-mysql-client python3-dev default-libmysqlclient-dev python3-mysqldb --fix-missing
pip3 install psycopg2 flask
ln /usr/bin/python3 /usr/bin/python -sf
ln /usr/bin/pip3 /usr/bin/pip -sf

To install dependencies, add the following line to the build command:

pip3 install --upgrade -r requirements.txt

For the app to deploy correctly, you may need to modify the start command to suit your project, specifying port binding, for example:

gunicorn main:app --timeout 60 --bind 0.0.0.0:80

Requirements

• Make sure the application initialization file (your app entry point) is named main.py.
• Make sure the application is listening on 0.0.0.0 rather than 127.0.0.1; otherwise, external connections will not work.

Troubleshooting

Deployment fails

If there are problems with deployment, first check the deployment log. You will be able to determine at what point something went wrong.

Most errors are usually related to:

• Missing main.py file or the app variable
• Incorrect start command
• Missing dependencies in requirements.txt

Make sure that the gunicorn main:app command runs successfully in your local environment.