Hey thanks! I wouldn't say it's a hard dependency, in fact it can work with other things that are API-compatible with DynamoDB, like Scylla for example if you wanted to self-host everything:

http://scylla.docs.scylladb.com/master/alternator/alternator

And in terms of using something like Firestore, the storage needs of this are very simple so it wouldn't be very hard to add that in. I tried to keep all the persistence-related functionality separated off, so it is swappable:

https://github.com/pickledish/cardi/tree/master/src/dynamodb