Yeah, we've had a PlanetScale cluster since the early days that powers the dashboard experience (turbopuffer.com/dashboard). That's a fairly standard webapp (customers, orgs, users, API keys, namespace stats) that benefits from the relational model.
When we built the cplane it was natural to just store the cplane ops in MySQL too. cplane ops belong to clusters which belong to customers, so it's actually rather nice to be able to foreign key it all together [0].
[0] Well, not actually enforced foreign keys, because Vitess, but you get the idea. It lets us apply settings at the customer level that flow to all ops for that customer's clusters.
When we built the cplane it was natural to just store the cplane ops in MySQL too. cplane ops belong to clusters which belong to customers, so it's actually rather nice to be able to foreign key it all together [0].
[0] Well, not actually enforced foreign keys, because Vitess, but you get the idea. It lets us apply settings at the customer level that flow to all ops for that customer's clusters.