You can use this module like as below example.
module "your_asg" {
source = "youngookkim/gcp/asg"
version = "v1.0.0"
name = "yourasg"
stack = "dev"
detail = "mk1"
region = "us-central1"
project = "bxb-plm-poc"
network = "${module.vpc.id}"
subnetwork = "${lookup(module.vpc.private_subnets_map, "us-central1")}"
ingress_rules = "${list(map("cidr", "0.0.0.0/0", "port", "443", "protocol", "tcp", "priority", "997"))}"
metadata = "${map("ansible-pull", "hello")}"
}