When you deploy projects containing VM instances that host your websites you have many options on how you decide to apply security protection. One of the method is using Cloud Armor but it requires you to setup a load balancer and not all of Google cloud users are familiar with it.
Another method is to integrate your on-premises firewall with Google cloud. Fortigate offers this feature in its security fabric connector.
In this video, I talked about the integration of Fortigate – Fortinet Firewall with Google cloud. Protect your applications, websites, and projects in Google cloud with Fortigate firewall.