Compute Savings Plans apply to EC2, AWS Fargate, and AWS Lambda usage, maximizing coverage for mixed architectures while retaining flexibility across instance families, regions, OS, and tenancy. For private connectivity, Lambda functions must be configured with VPC access to attach ENIs in the target subnets, enabling direct network access to EC2 in private subnets (no public subnets are required for intra-VPC communication). EC2 Instance Savings Plans only discount EC2 usage and are tied to a specific instance family in a region, reducing flexibility and leaving Lambda costs undiscounted. Keeping Lambda in the service VPC prevents direct access to private EC2 without VPC configuration. Thus, a 1-year Compute Savings Plan plus connecting Lambda to the private subnets minimizes total cost and meets connectivity needs.

References: AWS Savings Plans --- Compute Savings Plans applicability (EC2, Fargate, Lambda); AWS Lambda Developer Guide --- Configuring Lambda to access VPC resources (ENIs, subnets, security groups).