django-mysql-rds

django-mysql-rds

A Django db backend for connecting to RDS MySQL instances using SSL db auth tokens.

Use

I'd recommend understanding what you're doing and why before dropping this in, but chances are that you have a DATABASES dict that looks something like:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': DBNAME,
        'USER': USER,
        'PASSWORD': aws_client.generate_db_auth_token(HOST, PORT, USER),
        'HOST': HOST,
        'PORT': PORT,
        'OPTIONS': {
            'ssl': {
                'ca': 'certs/rds-cert.pem'
            }
        }
    }
}

And you've discovered that after ~15 minutes you make a request and receive Access Denied for user@instance because the password has expired.

This package allows you to generate the password at connection time by passing a callable instead:

def generate_pw():
    return aws_client.generate_db_auth_token(HOST, PORT, USER)

DATABASES = {
    'default': {
        'ENGINE': 'mysql_rds.backend',
        'NAME': DBNAME,
        'USER': USER,
        'PASSWORD': generate_pw,
        'HOST': HOST,
        'PORT': PORT,
        'CONN_MAX_AGE': 900,
        'OPTIONS': {
            'ssl': {
                'ca': 'certs/rds-cert.pem'
            }
        }
    }
}

I recommend setting a CONN_MAX_AGE of 900 as the generated auth token expires after 900 seconds. This ensures that connections requiring a refresh recreated. You can pass any function as the password and it will be evaluated at connection time. For testing locally if you cannot connect to directly to RDS you can do something like:

def generate_pw():
    return 'password'

Installation

$ pip install django-mysql-rds

or

$ git clone [e-mail]:cramshaw/django-mysql-rds.git

Why?

When I searched for a way to connect to an AWS RDS MySQL instance using SSL inside Django, I was unable to find anything that could handle the fact that the db auth token generated by AWS would expire every 15 minutes.

The problem is that when anything in the settings module changes, Django needs to reload. This isn't practical in a long running web app. I needed a way for the password to be generated at the time of connection.

How?

On close inspection of the django.db.backends.mysql code, it became clear that the DatabaseWrapper.get_connection_params method takes the settings dict, and transforms it into the kwargs that are passed to mysql.connect. I have subclassed this and extended to recognise if the password passed in is a callable, and if so, to call it and pass on the returned value. This leads to Django receiving a fresh password every time a connection is created.

A very similar thing happens in the DatabaseClient.settings_to_cmd_args which is used for things like dumping and loading data. This has also been subclassed and changed to ensure the password generation method actually runs before attempting to create a run a shell.

Caveats

Whilst this works for me running django==2.2 and should work exactly the same as the built in MySQL backend, there are no guarantees.

I only needed this to work for MySQL. I haven't explored whether RDS does the same for Postgres or other databases, but the same principle ought to apply.

Running Tests

Tests require mysqlclient installed.

$ brew install mysql-client
$ export PATH="/usr/local/opt/mysql-client/bin:$PATH"

Then to run:

$ python -m unittest tests/test*

Packaging

Bump version in setup.py then:

$ rm -rf dist/
$ python3 setup.py sdist bdist_wheel
$ python3 -m twine upload dist/*