{"id":161,"date":"2018-03-03T18:48:25","date_gmt":"2018-03-03T10:48:25","guid":{"rendered":"https:\/\/www.techcoil.com\/blog\/?p=161"},"modified":"2018-03-04T21:35:17","modified_gmt":"2018-03-04T13:35:17","slug":"how-to-deploy-python-3-flask-application-on-raspberry-pi-3-with-raspbian-stretch-lite-nginx-supervisor-virtualenv-and-gunicorn","status":"publish","type":"post","link":"https:\/\/www.techcoil.com\/blog\/how-to-deploy-python-3-flask-application-on-raspberry-pi-3-with-raspbian-stretch-lite-nginx-supervisor-virtualenv-and-gunicorn\/","title":{"rendered":"How to deploy Python 3 Flask application on Raspberry Pi 3 with Raspbian Stretch Lite, Nginx, Supervisor, Virtualenv and Gunicorn"},"content":{"rendered":"

Raspberry Pi 3 Model B boards<\/a> make good gifts for programmers<\/a> and if someone had gifted you with one, you may want to use it as a control center for interacting with various IoT sensors and devices at home.<\/p>\n

In such a situation, you may want to build a Python 3 Flask<\/a> application to present the web interface for accessing the control center.<\/p>\n

After you had built that Python 3 Flask application, the next step will be to deploy it on your Raspberry Pi 3 for serving HTTP requests. <\/p>\n

This post discusses how you can deploy a Python 3 Flask application on Raspberry Pi 3 with Raspbian Stretch Lite, Nginx<\/a>, Virtualenv<\/a> and Gunicorn<\/a>.<\/p>\n

Creating a simple Python 3 Flask application as a proof of concept<\/h2>\n

Let us create a simple Python 3 Flask application to demonstrate the deployment of Python 3 Flask application on our Raspberry Pi 3 with Raspbian Stretch Lite, Nginx, Supervisor, Virtualenv and Gunicorn.<\/p>\n

Project structure of our simple Python 3 Flask application<\/h3>\n

The simple application consists of a directory with the following contents:<\/p>\n

\r\nsimpleapp\r\n|--requirements.txt\r\n|--start.sh\r\n|--src\r\n   |--__init__.py\r\n|--static\r\n<\/pre>\n
Specifying Flask as a dependency in requirements.txt<\/code><\/h3>\n
The requirements.txt<\/code> file is for specifying the Python 3 dependencies that our Python 3 Flask application is going to need. Since this is a minimalistic application, the requirements.txt<\/code> contains only the following line:<\/p>\n
\r\nFlask==0.12.2\r\n<\/pre>\n
Creating start.sh for Supervisor to start the Python 3 Flask application<\/h3>\n
The shell script is intended for the Supervisor daemon to start our Python 3 Flask application. The shell script contains the following content:<\/p>\n
\r\nsource simpleappenv\/bin\/activate\r\ngunicorn --workers 5 --bind unix:simpleapp.sock -m 007 src:app\r\ndeactivate\r\n<\/pre>\n
The simpleappenv<\/code> directory contains a virtual environment that we will created later with virtualenv<\/code><\/a>. In this shell script, we first get into the virtual environment by sourcing the activate<\/code> script that resides in simpleappenv\/bin<\/code> directory. <\/p>\n
Once the virtual environment is activated, we will then use the gunicorn<\/code> binary to run our Python 3 Flask application. The command tells Gunicorn to use 5 workers for handling HTTP requests directed at the Python 3 Flask application. Gunicorn will listen for HTTP requests via the simpleapp.sock<\/code> unix socket. Only processes running the same user as this start.sh script can communicate with Gunicorn through the simpleapp.sock<\/code> unix socket. Gunicorn will also look into the src<\/code> package to find an app<\/code> variable to realise the Python 3 Flask application.<\/p>\n
We will install a version of gunicorn that can run Python 3 applications into the virtual environment later. <\/p>\n
The deactivate<\/code> command will be run when the Python 3 Flask application got terminated by whatever reason. In such a case, the executor of the shell script will get out of the virtual environment.<\/p>\n
Building the Python 3 Flask application inside src\/__init__.py<\/code><\/h3>\n
The src\/__init__.py<\/code> Python script will be run when the src<\/code> directory is being read by Python. The src\/__init__.py<\/code> file contains the following Python code:<\/p>\n
\r\nfrom flask import Flask\r\napp = Flask(__name__)\r\n \r\n@app.route('\/')\r\ndef hello_world():\r\n    return 'Hello there, welcome to our app!'\r\n<\/pre>\n
In this file, we import Flask, construct a Flask object and set it to the app<\/code> variable. We then decorate a function to return the message Hello there, welcome to our app!<\/strong> for HTTP requests directed at the root URL.<\/p>\n
Using the static<\/code> directory to serve as the root directory for Nginx<\/h3>\n
The static<\/code> directory is meant to serve as the root directory for Nginx. We will use this directory to keep images, CSS, JavaScript and other kinds of static files.<\/p>\n
Setting up Raspbian Stretch Lite on Raspberry Pi 3 to run Python 3 applications<\/h2>\n
As a first step to the deployment of your Python 3 Flask application, follow this tutorial to setup Raspbian Stretch Lite on Raspberry Pi 3 to run Python 3 applications<\/a>. After doing so, you will get your Raspberry Pi 3 running the Raspbian Stretch Lite operating system with the following software pieces:<\/p>\n