How to open a specific port such as 9090 in Google Compute Engine

Question

I have 2 Google Compute Engine instances and I want to open port 9090 in both the instances. I think we need to add some firewall rules.

Can you tell me how can I

Answer 1

I had to fix this by decreasing the priority (making it higher). This caused an immediate response. Not what I was expecting, but it worked.