To enable secure communication between a serverless function (such as AWS Lambda) and a relational database instance located within a private subnet of a Virtual Private Cloud (VPC), the developer must configure the serverless function with the specific network settings corresponding to that VPC. This includes the ID of the VPC, the subnets within the VPC where the database is situated, and the security groups that govern the allowed network traffic to and from the serverless function. This will provide the network path necessary for the function to access the database without exposing it to the public internet. Increasing the function's memory does not directly enable network connectivity to the VPC resources. A VPC Peering connection is unnecessary and inappropriate when both resources are in the same VPC. Opening public access to the database contradicts the requirement for private access and raises significant security risks.