Why am I getting the "MySQL server has gone away" exception in Django?

I'm working with Django 2.2.6.

The same system that runs my django project also has a background service running, listening on a unix socket for requests. In Django Admin, if a user hits a button, Django sends a request on the unix socket, and the background service does something.

My background service has full access to Django's ORM. It imports models from my project's models.py, and can query the database without any issues.

The problem is that if I leave my django, and my background service running overnight, login to Django Admin, and hit the button, my background service throws an exception:

django.db.utils.OperationalError: (2006, 'MySQL server has gone away')

It appears that this is because the MySQL database has a timeout period, called wait_timeout. If a connection to the database isn't active for that long, MySQL will disconnect it. Unfortunately, Django doesn't notice, and tries to use it, throwing the error.

Fortunately, Django has its own built-in CONN_MAX_AGE variable for each database defined in settings.py. If a database connection is older than the CONN_MAX_AGE, it shuts it down before a request and starts up a new one.

Looking at my MySQL database:

> show session variables where variable_name = "wait_timeout";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| wait_timeout  | 28800 |
+---------------+-------+

Looking at my Django's CONN_MAX_AGE variable:

# ./manage.py shell
>>> from django.conf import settings
>>> settings.DATABASES['default']['CONN_MAX_AGE']
0

Note: the 'default' database is the only one I have defined in my settings.py

Also note that both my MySQL wait_timeout, and my Django's CONN_MAX_AGE are default values - I haven't changed them.

According to the Django docs here, a CONN_MAX_AGE value of 0 means:

close database connections at the end of each request

If django is meant to close the database connection after every request, why than am I running into this error? Why isn't it closing old connections the second I'm done running my query, and starting a new connection when I do a new query, hours later?

from Why am I getting the "MySQL server has gone away" exception in Django?