Django multiple DB how to write router

Question

I've got two DB, I've written a router.py that correctly manage write and read, but if the read db the default is down I cannot access also the write db getting the

class TestRouter(object):

    def db_for_read(self, model, **hints):

        if model._meta.app_label == 'read_app':
            return 'default'
        if model._meta.app_label == 'write_app':
            return 'write_db'        
        return None

    def db_for_write(self, model, **hints):

        if model._meta.app_label == 'write_app':
            return 'write_db'
        return None

and in settings.py:

DATABASE_ROUTERS = ['prj.dbrouter.TestRouter', ]

this is the error:

cnn = _connect(dsn, connection_factory=connection_factory, async=async)
OperationalError: could not connect to server: Connection refused Is the server running on host "192.168.2.1" and accepting TCP/IP connections on port 5432?

is there a way to say to django to ignore failure in connection to default db?

Answer 1

Error shows that the database to which you want to connect is not accepting request or listening from host "192.168.2.1".

In postgresql.conf file, change listen_addresses = '*'

Lemme elaborate what exactly you should do,

1. Add the database information in your settings.py and also information about the routers.py :

settings.py

DATABASES = {
    'default': {},
    'master': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': '',
        'USER': '',
        'PASSWORD': '',
        'HOST': '',
        'PORT': 5432,
    },
    'slave': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': '',
        'USER': '',
        'PASSWORD': '',
        'HOST': '',
        'PORT': 5432,
    }
}
SLAVE_DATABASES = ['slave']

DATABASE_ROUTERS = ['path.to.your.routers.MasterSlaveRouter']

2. Create the routers.py which will handle switching the read and write request among the database mentioned in settings :

routers.py

from django.conf import settings
import socket


def test_connection_to_db(database_name):
    try:
        db_definition = getattr(settings, 'DATABASES')[database_name]
        s = socket.create_connection(
            (db_definition['HOST'], db_definition['PORT']), 5)
        s.close()
        return True
    except:
        return False


class MasterSlaveRouter(object):
    def db_for_read(self, model, **hints):
        """
        Reads go to a randomly-chosen slave.
        """
        if test_connection_to_db('master'):
            return 'master'
        return 'slave'

    def db_for_write(self, model, **hints):
        """
        Writes always go to master.
        """
        if test_connection_to_db('master'):
            return 'master'
        return 'slave'

    def allow_relation(self, obj1, obj2, **hints):
        """
        Relations between objects are allowed if both objects are
        in the master/slave 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, model):
        """
        All non-auth models end up in this pool.
        """
        return True

So now if your master is down and slave is up. Request will be transferred accordingly and vice-versa. Make sure any one database is up.

HTH! :)