gcloud alpha compute instance-groups unmanaged add-instances

NAME: gcloud alpha compute instance-groups unmanaged add-instances - adds instances to an unmanaged instance group by name
SYNOPSIS: gcloud alpha compute instance-groups unmanaged add-instances NAME --instances=INSTANCE,[INSTANCE,…] [--zone=ZONE] [GCLOUD_WIDE_FLAG …]
DESCRIPTION: (ALPHA) gcloud alpha compute instance-groups unmanaged add-instances adds existing instances to an unmanaged instance group by name. For example:
gcloud alpha compute instance-groups unmanaged add-instances my-group --instances my-instance-1,my-instance-2 --zone us-central1-a
POSITIONAL ARGUMENTS: NAME

Name of the instance group to operate on.
REQUIRED FLAGS: --instances=INSTANCE,[INSTANCE,…]

A list of names of instances to add to the instance group. These must exist beforehand and must live in the same zone as the instance group.
OPTIONAL FLAGS: --zone=ZONE

Zone of the instance group to operate on. If not specified and the compute/zone property isn't set, you might be prompted to select a zone (interactive mode only).
To avoid prompting when this flag is omitted, you can set the compute/zone property:
gcloud config set compute/zone ZONE

A list of zones can be fetched by running:
gcloud compute zones list

To unset the property, run:
gcloud config unset compute/zone

Alternatively, the zone can be stored in the environment variable CLOUDSDK_COMPUTE_ZONE.
GCLOUD WIDE FLAGS: These flags are available to all commands: --access-token-file, --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.
NOTES: This command is currently in alpha and might change without notice. If this command fails with API permission errors despite specifying the correct project, you might be trying to access an API with an invitation-only early access allowlist. These variants are also available:
gcloud compute instance-groups unmanaged add-instances

gcloud beta compute instance-groups unmanaged add-instances