Problem scenario
You are used to AWS Security Groups. You created a firewall rule in GCP. You cannot seem to reach the GCP server. What is wrong?
Possible Solution
Does the GCP firewall rule use the same shorthand notation like this?
x.x.x.x/32
Inbound rules in AWS Security Groups use the /32 to allow an IP address to connect to an EC-2 instance or service. For GCP, this /32 will not work. Use /24 or something along those lines.
You may want to see this "How Do You Get a GCP Server to Present a Website on the Internet?" for details.