The big innovation of aurora is they decoupled the compute from the storage [1]. Both compute and storage need to auto scale, but compute is the really important one that is hardest. Aurora serverless scales the compute automatically by keeping warm pools of db capacity around [2]. This is great for spiky traffic without degraded performance.

1. https://www.allthingsdistributed.com/files/p1041-verbitski.p... 2. https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide...