Deploying a Flask App

Last updated May 14, 2024

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

Application Build
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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
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  • 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
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Deployment fails
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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.