django-multidb-router 0.11

django-multidb-router

multidb provides two Django database routers useful in primary-replica database deployments.

DATABASES = {
    'default': {...},
    'shadow-1': {...},
    'shadow-2': {...},
}
REPLICA_DATABASES = ['shadow-1', 'shadow-2']

DATABASE_ROUTERS = ('multidb.ReplicaRouter',)

from django.db import connections
import multidb

connection = connections[multidb.get_replica()]

Caveats

PinningRouterMiddleware identifies database writes primarily by request type, assuming that requests with HTTP methods that are not GET, TRACE, HEAD, or OPTIONS are writes. You can indicate that any view writes to the database by using the multidb.db_write decorator. This will cause the same result as if the request were, e.g., a POST.

You can also manually set response._db_write = True to indicate that a write occurred. This will not result in using the default database in this request, but only in the next request.

Configuration

To use PinningReplicaRouter, put it into DATABASE_ROUTERS in your settings:

DATABASE_ROUTERS = ('multidb.PinningReplicaRouter',)

Then, install the middleware. It must be listed before any other middleware which performs database writes:

MIDDLEWARE_CLASSES = (
    'multidb.middleware.PinningRouterMiddleware',
    ...more middleware here...
)

PinningRouterMiddleware attaches a cookie to any user agent who has just written. The cookie should be set to expire at a time longer than your replication lag. By default, its value is a conservative 15 seconds, but it can be adjusted like so:

MULTIDB_PINNING_SECONDS = 5

If you need to change the name of the cookie, use the MULTIDB_PINNING_COOKIE setting:

MULTIDB_PINNING_COOKIE = 'multidb_pin_writes'

You may also set the ‘Secure’, ‘HttpOnly’, and ‘SameSite’ cookie attributes by using the following settings. These settings are based on Django’s settings for the session and CSRF cookies:

MULTIDB_PINNING_COOKIE_SECURE = False
MULTIDB_PINNING_COOKIE_HTTPONLY = False
MULTIDB_PINNING_COOKIE_SAMESITE = 'Lax'

Note: the ‘SameSite’ attribute is only available on django 2.1 and higher.

use_primary_db

multidb.pinning.use_primary_db is both a context manager and a decorator for wrapping code to use the primary database. You can use it as a context manager:

from multidb.pinning import use_primary_db

with use_primary_db:
    touch_the_database()
touch_another_database()

or as a decorator:

from multidb.pinning import use_primary_db

@use_primary_db
def func(*args, **kw):
    """Touches the primary database."""

pip install -r requirements.txt
./run.sh test