public function instanceConfigurations(array $options = [])
    {
        $resultLimit = $this->pluck('resultLimit', $options, false) ?: 0;

        return new ItemIterator(
            new PageIterator(
                function (array $config) {
                    return $this->instanceConfiguration($config['name'], $config);
                },
                [$this->connection, 'listInstanceConfigs'],
                ['projectId' => InstanceAdminClient::projectName($this->projectId)] + $options,
                [
                    'itemsKey' => 'instanceConfigs',
                    'resultLimit' => $resultLimit
                ]
            )
        );
    }