Your company's web server administrator is migrating on-premises backend servers for an application to GCP.

Create a managed instance group from one of the images of the on-premises servers, and link this instance group to a target pool behind your load balancer.

Create a target pool, add all backend instances to this target pool, and deploy the target pool behind your load balancer.

Deploy a third-party virtual appliance as frontend to these servers that will accommodate the significant differences between these backend servers.

Use GCP's ECMP capability to load-balance traffic to the backend servers by installing multiple equal-priority static routes to the backend servers.