No external database. It does use SQLite, which is okay unless you’re making a SaaS with thousands of users, and maybe even more, given it uses RabbitMQ for the writes. [1]
The Compose file sets up a volume for it, so the data is persisted correctly.
[1]: If everything’s set up correctly, there shouldn’t be concurrent writes to the SQLite db, and it should scale pretty well then. (The RabbitMQ + SQLite stack is a bit weird, I agree.)
