Troubleshooting S3 Access in Private Subnet
Question
Your company has a set of instances hosted in a private subnet.
These instances need to make calls to the Simple Storage Service.
You have set up the endpoint but cannot reach the S3 buckets from the instances in the private subnet.
Which of the following could be issues for the access? Choose 2 answers from the options given below.
Answers
Explanations
Click on the arrows to vote for the correct answer
A. B. C. D.Answer - B and D.
The prefix for the gateway endpoint needs to be added to the Route table.
The below diagram from the AWS Documentation shows the design of an endpoint.
Option A is incorrect because you should use a gateway for S3.
Option C is incorrect because the prefix should be attached to the Route table and not to the network interface.
For more information on VPC gateway endpoints, please visit the below URL:
https://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/vpce-gateway.html
The issue here is that instances in a private subnet do not have direct access to the internet, and hence they cannot reach services outside the VPC unless there is a specific configuration in place. In this case, we have an S3 endpoint set up, but the instances in the private subnet are not able to reach the S3 buckets.
To resolve this issue, we need to ensure that the following configuration is in place:
An S3 VPC endpoint should be created and attached to the VPC. This will allow the instances in the VPC to connect to S3 without needing to traverse the internet.
The prefix for the S3 endpoint needs to be added to the route table associated with the private subnet. This will ensure that traffic destined for S3 is routed through the endpoint.
If using VPC endpoints, ensure that the prefix for the endpoint is attached to the network interface for the instance. This will ensure that traffic from the instance is sent to the endpoint.
Based on the above information, the two possible issues that could be causing the access issue are:
B. The prefix for the endpoint is not attached to the Route table: If the route table associated with the private subnet does not have the prefix for the S3 endpoint, then the traffic from the instances will not be routed through the endpoint.
C. The prefix for the endpoint is not attached to the Network Interface: If the network interface for the instance does not have the prefix for the S3 endpoint, then traffic from the instance will not be sent to the endpoint.
A and D are not relevant to this issue, as they relate to different configurations. Interface endpoints are used for services that are not available over a gateway endpoint, and attaching an endpoint to the wrong VPC would result in the endpoint being inaccessible, but neither of these issues is related to the current situation.