Your VPC consists of public and private subnets. The private subnets make use of a NAT instance to download updates from the internet. The Instances are trying to download updates from a server that listens on port 8090. But the instances are not able to reach the external server for updates. Which of the following could be relevant issues with this? Choose 3 answers from the options given below.

Answer options:

A.The NAT instance is blocking outbound traffic on port 8090.
B.The Inbound NACL is blocking traffic on ephemeral ports.
C.The Inbound Security Groups are blocking traffic on port 8090.
D.The remote server firewall is blocking traffic.

Answer - A, B and D
The NAT instance could be blocking Outbound Traffic on port 8090 which is not allowing traffic to flow outwards.
The server will answer the request from its port 8090 ( source ). Therefore, the Inbound NACL needs to authorize this incoming traffic from an ephemeral port.
The remote server could also be blocking traffic from the instances.
Option C is invalid because the traffic needs to be authorized by the NACL.
For more information on NAT Instances, please visit the below URL:
https://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_NAT_Instance.html