How Multi-AZ cluster behaves for Storage class change ?

In Aurora Multi-AZ clusters, changing the storage class (e.g., gp2 → gp3) is applied seamlessly to all cluster nodes because Aurora storage is shared and distributed, so downtime is minimal to none.

If we change the Storage class of Primary , Do we face Downtime ?

Most storage class changes (gp2 → gp3) are applied online with minimal or no downtime, especially in Multi-AZ deployments, because the standby ensures high availability.

What will happen if we change the storage class from "gp2" to "gp3" of Primary DB instance ? Does the Standy also reflect the same ?

If we change the storage type of the primary RDS instance (e.g., from gp2 → gp3), the standby instance is automatically updated to match the same storage class. You don’t need to manually change the standby — AWS handles it for you.

In Multi-AZ deployment , Backups will be taken from Primary or Standy DB Instance ?

Standby DB instance because to avoid performance impact

Can we assign Route 53 private hoster zone for RDS located in Private Subnet ?

Yes, we can associate a Route 53 Private Hosted Zone with an RDS instance in a private subnet and it’s actually a best practice for private databases.