Question

Basically, to not have to worry about replication lag if a user is logged in, we want them to read/write to the master; but if the user is not logged in, we want them to read from the replica and write to the master. Is this possible using Django routers?

Answer 1

This might be bad practice, but at any point within your code, as long as you are using Django >= 1.2, with the using() method and using keyword, you have total control over which database select your QuerySets and do your saves and deletes.

For example, for a QuerySet:

>>> MyModel.objects.using('replica').all()

or saving an object:

>>> my_object.save(using='master')

So you could always do something like this in a view:

query_set = MyModel.objects.all()

if request.user.is_authenticated():
    query_set = query_set.using('master')

But this could get very cumbersome and should you decide to go along this road, you should seek a more elegant ways to mitigate it. Signals, middlewares and/or model managers come to mind.

See Manually selecting a database from the Django documentation.