Python web app example

Example of Python web app with a debian packaging.

Features:

• dh_virtualenv

  dh_virtualenv takes care of creating venv in the debian package with all Python dependencies. You can set up dependencies in setup.py which is then used to collect dependencies during the build and then distributed with your app bundle. It takes more space in your build and more time to create it, but brings stability without colision with installed Python packages on the server (becase of some tools for administrator or other application on shared web server).

• systemd

  Package also includes services to run uwsgi and nginx. This one is questionable. I prefer to distribute app which can be installed without any special configuration and cannot do any harm to other apps installed on the same server, so all my apps uses own nginx process. It uses more CPU, but usually it's not even noticeable. Start of the app is then as simple as systemctl statr webapp.

  Service for the proxy (nginx) is dependendy of the first one (uwsgi), which is started automatically. But when you need to do restart or other trick with the app, you need to call for example also systemctl stop webapp.proxy. Maybe little bit odd, but brings better maintenance options.

• Configuration files

  Both, uwsgi and nginx, have configuration in the package, which is good. I personaly like when I can install package without need to configure it on the server and keep configuration files separated. All configuration files are tracked in one repository. Easy to deploy.

  Same is valid for configuration files of application. See config module where is module for every environment. Same technique could be applied for any configuration file.

  Secure options, like secure key or credentials to the database, are handled by an environment.

• Scripts

  As systemd doesn't allow you to create custom commands for services, if you need some specific command, like database migrations, to be ready for you, just create business logic in your module and then specify your commands in your setup.py, in section console_scripts similarly like example script.

  Because of use of dh_virtualenv, script is installed in venv (/var/www/webapp/venv/webapp/bin/SCRIPT). To have that script handy in the system, write link also in debian/webapp.links as shown for an example script.

• Development Makefile

  During development is available Makefile which can be used to quickly run lint tools, tests, application in development mode or build the debian package. Makefile is designed to use a virtualenv and update dependencies every time you change them in setup.py. More about that in my blog post:

  https://blog.horejsek.com/makefile-with-python/

• Base Flask app

  For now it's very simple app, but shows usage of mypy, pytest, configuration files and database connection in Flask's global.

For more info you can go to my blog post about it:

https://blog.horejsek.com/python-packaging/

Development

To prepare your dev envrionment in Debian-like system, run this command:

(sudo) make prepare-dev

To run lint tools or tests, use this commands:

make lint
make test

To run web server in development mode:

make run

More useful commands can be explored by typing make.

Deployment

Create deb package and install it to your system:

make build
(sudo) make install

Start included service:

systemctl start webapp

That's it!

Docker

For comparison I included also simple docker version managed by docker-compose. I'm not big fan of docker--I don't think docker is answer for everything--but the ideas are the same. To have simple development environment and package for the deployment with included configuration files and services. The question is whether you need orchestration or just simple plain one instance.