Event-Based Mirroring: Automated per-Subnet Configuration

[chelma]

Description

Per design discussion in (#35), we currently require a human to intervene when the subnets within a User VPC change. This task is to convert the management of per-Subnet resources from a manual, CDK/CloudFormation operation to an automated, event-based, Lambda/AWS SDK operation.

This task will likely entail:

• Create new Rules to listen for VPC Service events that indicate a subnet configuration may have changed, and Lambdas to determine what subnet changes occurred
• Lambdas to handle new/removed Subnets by creating/destroying the per-Subnet mirroring resources
• Update the existing Rules/Lambdas to play nicely with the new behavior
• Update the add-vpc and remove-vpc code to use events rather than CDK/CloudFormation to handle per-Subnet resources

Acceptance Criteria

• Demonstrate the ability to gracefully handle the user adding a new subnet
• Demonstrate the ability to gracefully handle the user removing an existing, monitored subnet
• Demonstrate updated add-vpc and remove-vpc behavior works correctly