Ansible Inventory

• for recording and grouping of hosts 
• Dynamic
• where frequently a playbook will create a new cloud resource and then attempt to use it as if it were part of the inventory. This will fail, as the resource was not part of the inventory when the playbook launched. All is not lost though! A special module is provided that allows a playbook to temporarily add inventory to the in-memory inventory object, the add_host module

GCE dynamic inventory

https://docs.ansible.com/ansible/latest/scenario_guides/guide_gce.html. Except, it is slightly incomplete.
ansible.cfg also needs:

[defaults]
host_key_checking = False  # so as not to prompt for host key confirmation
private_key_file = /path/a/private_key  # a key that has a public key on the metadata for the project otherwise Ansible can’t connect
remote_user = ansible  # if the remote host is set to not allow root login
 
[inventory]
enable_plugins = gcp_compute
 
[ssh_connection]
retries = 6  # to give enough time and attempts to allow the instance to boot up fully

The “Wait for SSH to come up” task needs:

delay: 120
sleep: 10

to allow time for the machine to boot up

The gcp_compute_instance documentation is out-of-date.
network_interfaces.network and network_interfaces.subnetwork are maps not a strings. E.g.

network_interfaces:
    - network:
        selfLink: "{{ platform.network }}"

disks.boot is a required field for the first disk. E.g.

disks:
    - auto_delete: yes
      boot: yes

The returned object if formatted differently. For example,

…
  register: prototype_vm
- name: Wait for SSH for instance
  wait_for:
    delay: 120
    host: "{{ prototype_vm.networkInterfaces[0].networkIP }}"

More up-to-date documentation is in the source code: https://github.com/ansible/ansible/blob/devel/lib/ansible/modules/cloud/google/gcp_compute_instance.py#L30

Authentication isn’t explained very well. However, reading the source code it is clear that to use the service account assigned to the instance where Ansible will be ran from, the auth_kind needs to be application:

- name: Create an instance
  hosts: localhost
  gather_facts: no
  connection: local
  vars:
      auth_kind: application
 
  tasks:
    - include_tasks: tasks/to_create_instance.yml
 
- name: Configure prototype instance
  hosts: prototype_vms
  connection: ssh
  become: True
  roles:
    - role_to_configure_vm
 
- name: create prototype instance
  gcp_compute_instance:
    auth_kind: "{{ auth_kind }}"