devtrackers.gg
The "data migration" reference is probably TMI and will cause widespread panic, but for the sake of transparency, we wanted to provide a bit more detail than just "servers coming down for maintenance for up to 12 hours!".
That said, its literally a necessary database maintenance that just needed to happen. And given the time required, it there would be no ideal window that didn't impact someone's prime time.
This particular maintenance will not need to happen again for a long time.