You can save data transfer cost in AWS by creating a private hosted zone

Not by itself, since it's only DNS. But it can cut costs when your servers currently reach each other through public IPs or public domain names

Where the saving comes from: If `api.domain.in` resolves to an Elastic IP and another EC2 instance in the same VPC calls it:

• From a private subnet, the traffic goes through the NAT Gateway, which charges about $0.045/GB processing.
• Even without NAT, traffic to a public IP is billed as regional transfer, about $0.01/GB each way.

A private hosted zone (split-horizon) makes `api.domain.in` resolve to the private IP inside the VPC. The traffic then stays private: free within the same AZ, about $0.01/GB each way across AZs, and no NAT charge.

When it won't help

• AWS hostnames (`ec2-…amazonaws.com`, RDS endpoints) already resolve to private IPs inside the VPC.
• Traffic to users on the internet doesn't change.

Often a bigger win: S3 and DynamoDB gateway VPC endpoints are free and stop that traffic going through NAT.

Cost: about $0.50 per zone per month, plus query charges, which are negligible. To check, look in Cost Explorer for "NatGateway-Bytes" and "DataTransfer-Regional-Bytes".