You have an existing VPC in us-east-1. You have created a VPC Endpoint for S3 and added it to the main route table. You have launched an EC2 instance inside a subnet that is associated with the main route table. From the new EC2 instance, when requesting the S3 bucket within us-east-1, you noticed that the connection is failing. What could be the reason? ( Choose 2 options)

Answer options:

A.EC2 instance security group outbound rules are restricted and does not contain prefix list.
B.Main route table does not have internet gateway association.
C.Subnet’s Network ACL inbound rule does not allow traffic from S3.
D.Main route table does not have NAT gateway association.

Answer: A and C
For option A, By default, Amazon VPC security groups allow all outbound traffic unless you`ve specifically restricted outbound access.
For a gateway endpoint, if your security group`s outbound rules are restricted, you must add a rule that allows outbound traffic from your VPC to the service that`s specified in your endpoint. To do this, you can use the service`s prefix list ID as the destination in the outbound rule.
https://aws.amazon.com/premiumsupport/knowledge-center/connect-s3-vpc-endpoint/
So this option is correct.
For option B, when using the VPC endpoint for S3, an internet gateway is not required to route traffic to S3. VPC endpoint routes traffic internally within AWS without going out to the internet.
https://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/vpc-endpoints.html
So this option is incorrect.
For Option C, The default network ACL is configured to allow all traffic to flow in and out of the subnets with which it is associated. If your network ACL rules restrict traffic, you must specify the CIDR block ( IP address range ) for Amazon S3. So this option is correct.
For option D, when using the VPC endpoint for S3, the NAT gateway is not required to route traffic to S3. VPC endpoint routes traffic internally within AWS without going out to the internet. So this option is incorrect.