The most secure, scalable, and manageable method to grant SSH access to a specific group of users for a single instance is by using OS Login. OS Login links a user's Google identity with their VM's POSIX account and manages access through IAM roles.

By setting the instance metadata enable-oslogin=true, you activate this feature for that specific instance. Granting the roles/compute.osLogin IAM role to the dev1 group provides the necessary permissions for its members to establish an SSH connection to any instance with OS Login enabled, without granting them broader administrative privileges. This combination precisely meets the requirement of providing scoped access to the specified group.

B. This option is incomplete. While it correctly enables OS Login, it fails to grant the necessary IAM role (compute.osLogin) to the dev1 group, so the users would have no permission to connect.

C. This method is insecure and unscalable. It requires manually generating, distributing, and managing individual SSH keys for each user, which is prone to error and becomes a significant administrative burden as the group changes.

D. Sharing a single private SSH key among multiple users is a severe security anti-pattern. It eliminates individual accountability and makes key revocation and rotation extremely difficult if the key is compromised.

1. Google Cloud Documentation - About OS Login: "OS Login lets you use Compute Engine IAM roles to grant and revoke SSH access to your Linux instances... OS Login is the recommended way to manage many users across multiple instances or projects." This document also specifies that you enable OS Login by setting the enable-oslogin metadata value to TRUE.

Source: Google Cloud Documentation

"About OS Login".

2. Google Cloud Documentation - Set up OS Login: "After you enable OS Login on one or more instances in your project

you need to grant the necessary IAM roles to users." It lists roles/compute.osLogin as the role required to connect to instances.

Source: Google Cloud Documentation

"Set up OS Login"

Step 2: Grant necessary IAM roles.

3. Google Cloud Documentation - Compute Engine predefined IAM roles: The compute.osLogin role is described as providing "permissions to log in to Compute Engine instances using OS Login. This role does not grant administrator access." This confirms it as the appropriate least-privilege role.

Source: Google Cloud Documentation

"Compute Engine IAM roles"

Predefined roles table.

4. Google Cloud Documentation - Managing SSH keys in metadata: This document describes the manual method of managing keys and contrasts it with OS Login. It explains that blocking project-wide keys is a way to restrict access

but it still relies on manually adding instance-level keys

which is less manageable than OS Login.

Source: Google Cloud Documentation

"Managing SSH keys in metadata"

section "Instance-level public SSH keys".