You enable the VPC flow logs in one subnet. You use the ping command from your machine (203.0.113.12) to your EC2 instance (IP address is 172.31.16.140). The ping has failed, and you find below VPC flow logs:
2 123456789010 eni-1235b8ca123456789 203.0.113.12 172.31.16.140 0 0 1 4 336 1432917027 1432917142 ACCEPT OK
2 123456789010 eni-1235b8ca123456789 172.31.16.140 203.0.113.12 0 0 1 4 336 1432917094 1432917142 REJECT OK
Which configurations may result in this result?

Answer options:

A.The EC2 security group and the ACL in the EC2 subnet allow the inbound traffic. The security group denies the outbound traffic.
B.The EC2 security group and the ACL in the EC2 subnet allow the inbound traffic. The ACL denies the outbound traffic.
C.The ACL in the EC2 subnet denies the inbound traffic. The EC2 security group allows the inbound traffic.
D.The EC2 security group denies the inbound traffic. The ACL in the EC2 subnet allows both inbound and outbound traffic.

Correct Answer – B
Check https://docs.aws.amazon.com/vpc/latest/userguide/flow-logs-records-examples.html#flow-log-example-security-groups for the flow log record examples.
Option A is incorrect: Because the security group is stateful. As it allows the incoming traffic, the outbound traffic is automatically allowed.
Option B is CORRECT: Because this ensures that the inbound traffic is accepted. For the outbound traffic, as the ACL denies it, the message will be rejected. The configurations align with the flow logs.
Option C is incorrect: In this scenario, the incoming ping message is accepted. So the ACL rule for the inbound traffic should allow it.
Option D is incorrect: The inbound rule in the security group should allow the traffic since there is an ACCEPT for the incoming message.