A SysOps administrator configures an Amazon S3 gateway endpoint in a VPC. The private subnets inside the VPC do not have outbound internet access. User logs in to an Amazon EC2 instance in one of the private subnets and cannot upload a file to an Amazon S3 bucket in the same AWS Region.
Which solution will solve this problem?
The EC2 instance in a private subnet without outbound internet access needs a route to the Amazon S3 gateway endpoint to communicate with an S3 bucket in the same AWS Region. By updating the route table associated with the private subnet to include the S3 prefix list destination routes to the S3 gateway endpoint, this ensures that network traffic intended for S3 is correctly directed through the endpoint and not tried to be sent to the internet. This resolves the issue of uploading a file to the S3 bucket.
"For Route tables, select the route tables to be used by the endpoint. We automatically add a route that points traffic destined for the service to the endpoint network interface." https://docs.aws.amazon.com/vpc/latest/privatelink/vpc-endpoints-s3.html#associate-route-tables-s3 So route should be already enable by default, Change need to bedone in s3 bucket policy
why not C : route cannot solve issue (security or policy grant needed)
WHY NOT A or D. the issue is related to network connectivity, not permissions.
not necessarily. the question says the user cannot upload. the first thing I would check is obviously the bucket policy. being in a private subnet and using a S3 endpoint doesn't rely much on the network connectivity, does it?
When you create a gateway endpoint, you select the VPC route tables for the subnets that you enable. The following route is automatically added to each route table that you select. The destination is a prefix list for the service owned by AWS and the target is the gateway endpoint.
I tackled a similar issue in work this week and I still couldn't confidently answer this. I click-ops a dummy network my findings: routes are by default, VPC -> local prefix list would apply to a SG. Endpoint policy by default allows absolutely everything. By default an s3 bucket has no policy.
In the question As the SysOps admin already configures an Amazon S3 gateway endpoint in a VPC then Updating the EC2 subnet route table to include the S3 prefix list destination routes to the S3 gateway endpoint is not required. So just Update the S3 bucket policy to allow s3:PutObject access from the private subnet CIDR block.
It’s C - subnet route table must have an entry pointing to the VPC gateway prefix.
C is the way here.
A - you need access to allow upload Put object. why not D ? well this is a potential cause, however, when you create S3 Gateway Endpoint you can associate your subnets and that creates a route automatically. https://docs.aws.amazon.com/vpc/latest/privatelink/vpc-endpoints-s3.html#create-gateway-endpoint-s3:~:text=For%20Route%20tables%2C%20select%20the%20route%20tables%20to%20be%20used%20by%20the%20endpoint.%20We%20automatically%20add%20a%20route%20that%20points%20traffic%20destined%20for%20the%20service%20to%20the%20endpoint%20network%20interface. Why not C ? Once traffic is routed via the S3 Gateway endpoint, then the private subnet CIDR is irrelevant.
https://repost.aws/knowledge-center/connect-s3-vpc-endpoint#:~:text=An%20outbound%20rule%20allowing%20traffic%20to%20the%20ID%20of%20the%20prefix%20list%20associated%20with%20the%20gateway%20VPC%20endpoint.
C makes the most sense here.
When an Amazon S3 gateway endpoint is configured in a VPC, the private subnets within the VPC need to have their route tables updated to route the S3 traffic to the gateway endpoint, instead of the internet. Without the appropriate route table updates, the EC2 instance in the private subnet will not be able to communicate with the S3 bucket, even if the instance has the necessary S3 permissions. Option A is incorrect because the issue is not related to the IAM role permissions, but rather the routing configuration. Option B is incorrect because allowing outbound traffic to 0.0.0.0/0 on port 80 is not necessary to solve this problem. The issue is with the routing to the S3 gateway endpoint, not the internet access. Option D is incorrect because the S3 bucket policy is not the issue here. The problem is with the routing, not the permissions on the S3 bucket.
Why Option C is Essential: Directing Traffic to S3: Without the correct route in the subnet’s route table, the instance cannot send traffic to S3 because it doesn’t know that it should use the gateway endpoint. Using the Gateway Endpoint: The S3 gateway endpoint enables access to S3 without internet. For this to work, the route table must have a route for the S3 prefix list pointing to the endpoint. Why Option D Alone is Insufficient: Access Control vs. Network Path: S3 Bucket Policy: Controls who (or what) can access the bucket and perform specific actions (e.g., s3:PutObject). While necessary for access control, it does not configure the network path needed for the EC2 instance to reach S3. Network Configuration: Ensures that there is a valid route for the traffic from the EC2 instance to S3.
To resolve the issue where a user cannot upload a file to an Amazon S3 bucket from an Amazon EC2 instance in a private subnet without outbound internet access, even with an S3 gateway endpoint configured, you should: C. Update the EC2 subnet route table to include the S3 prefix list destination routes to the S3 gateway endpoint. The primary step needed here is to ensure that the route table associated with the private subnet where the EC2 instance resides correctly routes S3 traffic to the S3 gateway endpoint, enabling secure, private connectivity to S3.
The answer is C: Each subnet route table must have a route that sends traffic destined for the service to the gateway endpoint using the prefix list for the service https://docs.aws.amazon.com/vpc/latest/privatelink/gateway-endpoints.html
Why not A? Its actually A and C.