Even though they’re in the same region, by default their communication will still be done through the public internet which may result in higher latency and data transfer fees.

To avoid these inconveniences you need to enable traffic to use private IPs over AWS internal network by setting up VPC Peering.

You can learn how to enable VPC Peering in the official documentation: https://redis.io/docs/latest/operate/rc/security/vpc-peering/