gcloud alpha compute reservations set-iam-policy

gcloud alpha compute reservations set-iam-policy - set the IAM policy for a Compute Engine reservation
gcloud alpha compute reservations set-iam-policy (RESERVATION : --zone=ZONE) POLICY_FILE [GCLOUD_WIDE_FLAG]
(ALPHA) Set the IAM policy for the given reservation as defined in a JSON or YAML file.
Reservation resource - The reservation to set the IAM policy for. The arguments in this group can be used to specify the attributes of this resource. (NOTE) Some attributes are not given arguments in this group but can be set in other ways. To set the [project] attribute: provide the argument [reservation] on the command line with a fully specified name; set the property [core/project]; provide the argument [--project] on the command line. This must be specified.
ID of the reservation or fully qualified identifier for the reservation. This positional must be specified if any of the other arguments in this group are specified.
The name of the Google Compute Engine zone.
Path to a local JSON or YAML formatted file containing a valid policy.

The output of the get-iam-policy command is a valid file, as is any JSON or YAML file conforming to the structure of a Policy.

These flags are available to all commands: --account, --billing-project, --configuration, --flags-file, --flatten, --format, --help, --impersonate-service-account, --log-http, --project, --quiet, --trace-token, --user-output-enabled, --verbosity.

Run $ gcloud help for details.

This command uses the compute/alpha API. The full documentation for this API can be found at: https://developers.google.com/compute/docs/reference/latest/
The following command will read am IAM policy defined in a JSON file 'policy.json' and set it for the reservation my-reservation:
gcloud alpha compute reservations set-iam-policy my-reservation  --zone=ZONE policy.json

See https://cloud.google.com/iam/docs/managing-policies for details of the policy file format and contents.

This command is currently in ALPHA and may change without notice. If this command fails with API permission errors despite specifying the right project, you may be trying to access an API with an invitation-only early access allowlist. These variants are also available:
gcloud compute reservations set-iam-policy
gcloud beta compute reservations set-iam-policy