A backend is simply a store for objects. It needs to support four operations:
There are a few other operations, like deleting an entry, that are useful, but not strictly necessary.
Backends are identified by a URI type string, generically called jugdir. For example, to connect to a redis backend, use redis:host:port/database. Your backend should support a similar scheme.
You can start with the file jug/backends/generic.py which provides a template with documentation. Implement the functions in there.