def METHOD_NAME(cli_ctx, aks, resource_group_name):
    from msrestazure.tools import is_valid_resource_id
    aks_is_id = is_valid_resource_id(aks)
    if aks_is_id:
        return aks
    if aks and not aks_is_id:
        from msrestazure.tools import resource_id
        from azure.cli.core.commands.client_factory import get_subscription_id
        return resource_id(
            subscription=get_subscription_id(cli_ctx),
            resource_group=resource_group_name,
            namespace='Microsoft.ContainerService',
            type='managedClusters',
            name=aks)
    raise ArgumentUsageError('Usage error: --aks')