A. Create a new security group in the database VPC and create an inbound rule that allows all traffic from the IP address range of the application VPC. Add a new network ACL rule on the database subnets. Configure the rule to TCP port 1521 from the IP address range of the application VPC. Attach the new security group to the database instances that the application instances need to access.
B. Create a new security group in the application VPC with an inbound rule that allows the IP address range of the database VPC over TCP port 1521. Create a new security group in the database VPC with an inbound rule that allows the IP address range of the application VPC over port 1521. Attach the new security group to the database instances and the application instances that need database access.
C. Create a new security group in the application VPC with no inbound rules. Create a new security group in the database VPC with an inbound rule that allows TCP port 1521 from the new application security group in the application VPC. Attach the application security group to the application instances that need database access, and attach the database security group to the database instances.
D. Create a new security group in the application VPC with an inbound rule that allows the IP address range of the database VPC over TCP port 1521. Add a new network ACL rule on the database subnets. Configure the rule to allow all traffic from the IP address range of the application VPC. Attach the new security group to the application instances that need database access.