Source: 📖 Test Driven Development with Python ch11 p189

Using fabric to automate deployment

fabric is a python package that can be pip-installed. It can be used to run shell commands with the run function as follows:

from fabric.api import run

source_dir = 'home/ubuntu/sites/staging.mysite.com/source'

run(f'mkdir -p {source_dir}/newdir')

It also has a sed function that allows us to substitute a string in a file:

from fabric.contrib.files import sed


SITENAME = 'juancoquet.com'

path_to_settings = 'my_django_project/settings.py'

# Set DEBUG to False for deployment
sed(path_to_settings, "DEBUG = True", "DEBUG = False")

# Set ALLOWED_HOSTS
sed(path_to_settings, "ALLOWED_HOSTS = []", f'ALLOWED_HOSTS = ["{SITENAME}"]')

For deployment, it is good practice to ensure that the SECRET_KEY constant in settings.py is different on the server than it is on your local repository, as the local repository may be visible by others through github. This can be done in the following manner:

from fabric.contrib.files import append, exists
import random


secret_key_file = 'path/to/secret_key.py'

if not exists(secret_key_file):
	chars = 'abcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*(-_=+)'
	key = ''.join(random.SystemRandom().choice(chars) for _ in range(50))
	append(secret_key_file, f'SECRET_KEY = "{key}"')
append(path_to_settings, '\nfrom .secret_key import SECRET_KEY')

We first check if a secret_key.py file already exists to see if we have already made a secret key for the server. If it doesn't, we generate a random key and create a file to contain it in a SECRET_KEY constant. We use the SystemRandom() class from the random package to select random characters from chars in a cryptographically safe way (the usual random.choice() is not safe). Finally, we import SECRET_KEY into settings.py.