Currently, a single-backend application will need to do this:
We could simplify it to this:
A few details:
We would have to give a name to this default backend. default, maybe? In that case we should forbid the use of that name for named backends.
Existing applications relying on default_backend should continue to work, but maybe we should deprecate this configuration property. People who really need to define the default backend at deployment time can use the programmatic mapping.
We should still allow the definition of named backends, but they will only be used when explicitly referenced.
We should use the default backend wherever possible in tests and documentation, and add separate tests and documention for named backends.
In examples for setting configuration properties, we should only include an example for the default backend. We'll just mention in the section about named backends how the prefix changes for those.