Amazon RDS removes the headaches of running a relational database reliably at scale, allowing Amazon RDS customers to focus on innovation for their customers. Read Replicas enables you to elastically scale out beyond the capacity constraints of a single DB Instance for read-heavy database workloads.
You can now create one or more replicas of a given “source” DB Instance and serve incoming read traffic from multiple copies of your data within a VPC environment. You can create a Read Replica with a few clicks of the AWS Management Console or using the CreateDBInstanceReadReplica API.
Amazon VPC allows you to customize the network configuration to closely resemble a traditional network that you might operate in your own datacenter. I described the process of launching a DB Instance inside of a VPC in an earlier post.
Amazon RDS in VPC enables you to have a DB instance within a private network powering a public web application. The DB instance is on a private subnet, which does not have a public IP address. You can also use Amazon RDS + VPC to run corporate applications that are not intended to be accessed from the Internet.