The ECS security group must allow inbound HTTPS traffic. For an inbound security-group rule, the Internet clients are the source, so the correct rule permits TCP destination port 443 from source 0.0.0.0/0. This makes Option C correct. Alibaba Cloud security groups are stateful, which means response traffic belonging to an allowed connection is automatically permitted and does not require a matching outbound security-group rule.

Network ACLs behave differently. Alibaba Cloud VPC network ACLs are stateless. If the ACL permits an inbound HTTPS request but does not permit the corresponding return packet, the TCP session cannot operate correctly. The inbound ACL therefore needs TCP 443 from Internet clients, while the outbound ACL must permit return traffic to client ephemeral destination ports. Alibaba Cloud explicitly recommends 1024–65535 when all client ephemeral-port implementations must be supported.

Option D permits only the incoming side of the ACL and therefore fails because response packets remain blocked. Option E incorrectly assumes that outbound server responses use destination port 443; the server ' s source port is 443, but the destination is the client ' s ephemeral port.

Study Guide reference: Securing Workloads on Alibaba Cloud — stateful Security Groups, stateless network ACLs, HTTPS exposure, and ephemeral ports.

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