Плохая практика фаер на инстансе держать, вообще фаер на инстансе никуда не упал и не надо именно на инстансе настраивать
Use iptables and routes to limit or filter egress traffic
While the Cloud Platform firewall rules can control ingress traffic to your VM instances, network routes can control egress from VMs to IP address ranges. Examples include routing all external traffic through a NAT gateway, all traffic to corporate IP ranges through a VPN gateway, or denying access to IP ranges by routing to a non-existent IP. If you require control over the egress traffic from the VM instances to specific ports, such as filtering all traffic through port 80, configure iptables or another host-based filtering mechanism on the instance.
https://cloud.google.com/docs/enterprise/best-practices-for-enterprise-organizations