What's the best way to implement DB Router in Django? - django

Question

I have implemented Automatic DB Routing in Django and using AWS Aurora for Database with replication. I have found a minor replication lag with my database which hampering the flow. Issue occurs let's say when a read queryset is getting executed with 'slave' then while updating value using that queryset showing error something like 'read-only access for that table.' that means for update it should route to master db.
Here is my DB Settings for Multiple DB:
DATABASES = {
'master': {
'ENGINE': 'django.db.backends.mysql',
'STORAGE_ENGINE': 'MyISAM / INNODB / ETC',
'NAME': 'db',
'USER': 'master',
'PASSWORD': 'master',
'HOST': 'localhost',
'PORT': '3306',
},
'slave': {
'ENGINE': 'django.db.backends.mysql',
'STORAGE_ENGINE': 'MyISAM / INNODB / ETC',
'NAME': 'db',
'USER': 'name',
'PASSWORD': 'pass',
'HOST': 'localhost',
'PORT': '3306',
},
'slave2': {
'ENGINE': 'django.db.backends.mysql',
'STORAGE_ENGINE': 'MyISAM / INNODB / ETC',
'NAME': 'db',
'USER': 'name',
'PASSWORD': 'pass',
'HOST': 'localhost',
'PORT': '3306',
}
}
DATABASE_ROUTERS = ['path.to.AuthRouter']
Please provide me the best way to handle multiple db route automatically in django.
"""
DB Router core class which auto selects required database configuration
"""
class AuthRouter:
def db_for_read(self, model, **hints):
"""
Reads go to a replica.
"""
print 'db_for_read'
print model
return 'slave'
def db_for_write(self, model, **hints):
"""
Writes always go to master ie default.
"""
print 'db_for_write'
print model
return 'master'
def allow_relation(self, obj1, obj2, **hints):
"""
Relations between objects are allowed if both objects are
in the default/replica pool.
"""
db_list = ('master', 'slave')
if obj1._state.db in db_list and obj2._state.db in db_list:
return True
return None
def allow_migrate(self, db, app_label, model_name=None, **hints):
"""
All non-auth models end up in this pool.
"""
return True

Answer 1

You can split the read operations and isolate the writing operations for master DB like:
AuthRouter should call master DB since that's the fresh information from users.
class AuthRouter:
def db_for_read(self, model, **hints):
"""
Reads go to a replica.
"""
return 'master'
def db_for_write(self, model, **hints):
"""
Writes always go to master ie default.
"""
return 'master'
def allow_relation(self, obj1, obj2, **hints):
"""
Relations between objects are allowed if both objects are
in the default/replica pool.
"""
db_list = ('master', 'slave')
if obj1._state.db in db_list and obj2._state.db in db_list:
return True
return None
def allow_migrate(self, db, app_label, model_name=None, **hints):
"""
All non-auth models end up in this pool.
"""
return True
class PrimaryReplicaRouter(object):
"""
A router to control all read/write database operations.
"""
def db_for_read(self, model, **hints):
"""
Reads go to a randomly-chosen replica.
"""
return select_rand_db()
def db_for_write(self, model, **hints):
"""
Writes always go to primary.
"""
return 'master'
def allow_relation(self, obj1, obj2, **hints):
"""
Relations between objects are allowed if both objects are
in the primary/replica pool.
"""
return True
def allow_migrate(self, db, app_label, model_name=None, **hints):
"""
All non-auth models end up in this pool.
"""
return True
def select_rand_db():
from numpy.random import choice
"""
this function returns rand db or default if running tests
:return:
"""
return choice(['master', 'slave'], p=[0.5, 0.5])