With RDS Aurora, any of your read replicas can be promoted to read/write master in the event of a failure of your primary master. This happens in 10-15 seconds, and is very fast.
So, you can get the benefit of up to 15 read replicas, and not have to pay for an extra standby server that is sitting idle.
So, you can get the benefit of up to 15 read replicas, and not have to pay for an extra standby server that is sitting idle.