Troubleshooting Access Denied Error for VPC Endpoint to S3 Bucket

Answer - C.

Option A is incorrect since the default endpoint policy will already allow complete S3 access.

Option B is incorrect since the right approach is to add the VPC Endpoint to the S3 bucket policy.

Option D is incorrect since you are not supposed to add this to the Bucket ACL.

You need to ensure that the S3 bucket allows access to the VPC Endpoint.

Below is a sample from the AWS Documentation.

Restricting Access to a Specific VPC Endpoint.

The following is an example of an S3 bucket policy that restricts access to a specific bucket, examplebucket, only from the VPC endpoint with the ID vpce-1a2b3c4d.

The policy denies all access to the bucket if the specified endpoint is not being used.

The aws:sourceVpce condition is used to specify the endpoint.

The aws:sourceVpce condition does not require an ARN for the VPC endpoint resource, only the VPC endpoint ID.

For more information about using conditions in a policy, see Specifying Conditions in a Policy.

{

"Version": "2012-10-17",

"Id": "Policy1415115909152",

"Statement": [

{

"Sid": "Access-to-specific-VPCE-only",

"Principal": "*",

"Action": "s3:*",

"Effect": "Deny",

"Resource": ["arn:aws:s3:::examplebucket",

"arn:aws:s3:::examplebucket/*"],

"Condition": {

"StringNotEquals": {

"aws:sourceVpce": "vpce-1a2b3c4d"

}

}

}

]

}

For more information on VPC endpoints and S3 bucket policies, please refer to the below URL.

https://docs.aws.amazon.com/AmazonS3/latest/dev/example-bucket-policies-vpc-endpoint.html

In this scenario, you have created a VPC Endpoint to S3 in a private subnet. However, when trying to access the S3 bucket, you receive an "access denied" error. To resolve this issue, you need to modify the endpoint or bucket policy to allow access to the S3 bucket.

Firstly, you need to understand the difference between the endpoint policy and bucket policy in AWS.

Endpoint policy is a JSON-based policy that defines the permissions for a VPC Endpoint. It controls which resources can be accessed through the VPC Endpoint, and which actions are allowed or denied. When you create a VPC Endpoint, the default policy is applied, which allows full access to S3.

Bucket policy is also a JSON-based policy that defines the permissions for an S3 bucket. It controls who can access the bucket and what actions they can perform on the objects within the bucket.

Now let's go through the options:

A. Add the VPC endpoint to the Endpoint policy to allow access to the S3 bucket.

This option is correct. You need to add the VPC endpoint to the endpoint policy to allow access to the S3 bucket. By default, the VPC Endpoint policy allows full access to S3. However, you might have modified the policy, and you need to add the S3 bucket to the policy to allow access.

B. Add the VPC to the S3 bucket policy.

This option is incorrect. You do not add a VPC to an S3 bucket policy. The S3 bucket policy controls access to the bucket, and you need to modify it to allow access to the VPC Endpoint.

C. Add the VPC Endpoint to the S3 bucket policy.

This option is also correct. You can add the VPC Endpoint to the S3 bucket policy to allow access to the bucket. However, this is not the recommended approach because it limits the VPC Endpoint's access to only the specified S3 bucket.

D. Add the VPC endpoint to the Bucket ACL.

This option is incorrect. You do not add a VPC endpoint to the Bucket Access Control List (ACL). The Bucket ACL controls who can access the bucket, and you need to modify it to allow access to the VPC Endpoint.

To summarize, the correct options are A and C. You need to modify either the VPC Endpoint policy or the S3 bucket policy to allow access to the S3 bucket. It is recommended to modify the VPC Endpoint policy to allow access to all S3 buckets rather than adding the VPC Endpoint to each bucket policy.