We've engineered in protections from noisy neighbors in both CPU and I/O usage and we do not over-commit resources.

If your or another customer's workload grows and needs to size up we launch three whole new database servers of the appropriate size (whether that's more CPU+RAM, more storage, or both), restore the most recent backups there, catch up on replication, and then orchestrate changing the primary.

Downtime when you resize typically amounts to needing to reconnect i.e. it's negligible.