To enable Engineering Group A to attach a Compute Engine instance to a specific subnet (10.1.1.0/24) in a Shared VPC, you should grant the Compute Network User Role at the subnet level. This role allows users to use the subnetwork for their instances without giving them broader permissions at the project level.

Step-by-Step:

Identify the Subnet: Locate the subnet (10.1.1.0/24) in the host project.

Grant Role:

Navigate to the GCP Console > VPC network > VPC networks.

Select the Shared VPC host project and locate the specific subnet.

Click on "Edit" and go to the "IAM & Admin" section.

Assign the "Compute Network User" role to Engineering Group A at the subnet level.

Verification: Ensure that Engineering Group A can now attach Compute Engine instances to the specified subnet.