Troubleshooting VPC Endpoint Connectivity to S3 in us-east-1
Question
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)
Answers
Explanations
Click on the arrows to vote for the correct answer
A. B. C. D.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.htmlSo 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.
The two possible reasons why the connection to the S3 bucket is failing from the EC2 instance are:
B. Main route table does not have internet gateway association: If the main route table does not have an internet gateway association, the EC2 instance will not be able to access any services outside of the VPC, including S3. An internet gateway is required for traffic to go outside of the VPC, so if the main route table does not have an internet gateway association, the EC2 instance will not be able to communicate with the S3 bucket. To resolve this issue, you can associate an internet gateway with the VPC and update the main route table to include a route for all traffic to the internet gateway.
D. Main route table does not have NAT gateway association: If the main route table does not have a NAT gateway association and the EC2 instance is not in a private subnet with a NAT gateway, the EC2 instance will not be able to access S3 or any services outside of the VPC. A NAT gateway is used to provide internet access to resources in private subnets, so if the main route table does not have a NAT gateway association and the EC2 instance is not in a private subnet with a NAT gateway, the connection will fail. To resolve this issue, you can create a NAT gateway in a public subnet and associate it with the main route table.
The other options, A and C, are not correct in this scenario.
A. EC2 instance security group outbound rules are restricted and does not contain prefix list: This option is not related to the issue at hand. Security groups are used to control inbound and outbound traffic to instances, but prefix lists are not relevant to this issue.
C. Subnet's Network ACL inbound rule does not allow traffic from S3: This option is not correct because the VPC Endpoint for S3 has been created and added to the main route table. Therefore, the traffic to S3 should be routed through the VPC Endpoint and not through the subnet's Network ACL.
