Here’s how to create an instance with CUD (committed used discounts) reservations.
gcloud compute instances create instance-name \ --no-address \ --private-network-ip 10.0.0.24 \ --source-machine-image=projects/project-id/global/machineImages/image-name \ --subnet=https://www.googleapis.com/compute/v1/projects/your-project/regions/us-central1/subnetworks/your-sub-network \ --machine-type=n1-standard-4 \ --reservation-affinity=specific \ --reservation=your-reservation-name \ --zone=us-central1-a \ --project=your-project-id |