sourceServiceAccounts property

If source service accounts are specified, the firewall rules apply only to traffic originating from an instance with a service account in this list.

Source service accounts cannot be used to control traffic to an instance's external IP address because service accounts are associated with an instance, not an IP address. sourceRanges can be set at the same time as sourceServiceAccounts. If both are set, the firewall applies to traffic that has a source IP address within the sourceRanges OR a source IP that belongs to an instance with service account listed in sourceServiceAccount. The connection does not need to match both fields for the firewall to apply. sourceServiceAccounts cannot be used at the same time as sourceTags or targetTags.