Your organization’s Google Cloud VMs are deployed via an instance template that configures them with...

External HTTP(S) Load Balancer: Deploy an external HTTP(S) load balancer to manage traffic to your VMs. This load balancer will handle incoming traffic from the internet while the VMs themselves do not have public IP addresses.

Host (VPC) Project Deployment: Deploy the load balancer in the host (VPC) project. This allows for centralized management of network resources and maintains the integrity of your shared VPC configuration.

Backend Configuration: Configure the MIG as the backend for the load balancer. This setup ensures that the VMs can still serve external users while reducing their direct exposure to the internet. This solution provides the required access to external users through the load balancer, enhancing security by not exposing individual VM IP addresses. References:

Google Cloud - External HTTP(S) Load Balancer Overview

Google Cloud - Shared VPC Overview