The correct security-group design is to allow inbound database access from the EC2 instances’ security group rather than from individual IP addresses. AWS security groups can reference another security group as the source, which is the scalable and recommended approach for application-to-database communication in dynamic environments such as Auto Scaling groups. That way, newly launched instances automatically inherit access without requiring IP-based rule updates. Option A is brittle because private IPs change as instances scale. Option C is not how security-group rules are defined, and option D reverses the traffic direction. Therefore, allowing the database security group to accept traffic from the web-servers security group is the right architecture.

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