Create network tag app-server and service account sa-db@my-project.iam.gserviceaccount.com. Add the tag to the application servers, and associate the service account with the database servers. Run the following command: gcloud compute firewall-rules create app-db-firewall-rule \ --action allow \ --direction ingress \ --rules top:3306 \ --source-tags app-server \ --target-service-accounts sa-db@my- project.iam.gserviceaccount.com

Create service accounts sa-app@my-project.iam.gserviceaccount.com and sa-db@my-project.iam.gserviceaccount.com. Associate the service account sa-app with the application servers, and associate the service account sa-db with the database servers. Run the following command: gcloud compute firewall-rules create app-db-firewall-ru --allow TCP:3306 \ --source-ranges 10.128.0.0/20 \ --source-service-accounts sa-app@my- project.iam.gserviceaccount.com \ --target-service-accounts sa-db@my- project.iam.gserviceaccount.com

Create network tags app-server and db-server. Add the app-server tag to the application servers, and add the db-server tag to the database servers. Run the following command: gcloud compute firewall-rules create app-db-firewall-rule \ --action allow \ --direction ingress \ --rules tcp:3306 \ --source-ranges 10.128.0.0/20 \ --source-tags app-server \ --target-tags db-server