serviceLabel property

An optional prefix to the service name for this forwarding rule.

If specified, the prefix is the first label of the fully qualified service name. The label must be 1-63 characters long, and comply with RFC1035. Specifically, the label must be 1-63 characters long and match the regular expression [a-z]([-a-z0-9]*[a-z0-9])? which means the first character must be a lowercase letter, and all following characters must be a dash, lowercase letter, or digit, except the last character, which cannot be a dash. This field is only used for internal load balancing.