Why is my lambda function unable to access S3?

Question

I am creating AWS Lambda functions using the C++ SDK. I create these functions with the following role:

Role Document:

{
  "permissionsBoundary": {},
  "roleName": "my_role",
  "policies": [
    {
      "document": {
        "Version": "2012-10-17",
        "Statement": [
          {
            "Effect": "Allow",
            "Action": "s3:*",
            "Resource": "*"
          }
        ]
      },
      "name": "AmazonS3FullAccess",
      "id": "SOMEID",
      "type": "managed",
      "arn": "arn:aws:iam::aws:policy/AmazonS3FullAccess"
    }
  ],
  "trustedEntities": [
    "lambda.amazonaws.com"
  ]
}

When it comes to permissions that's all I do. My lambda functions is still unable to access S3, though. Why is that?

Do I have to create a policy that lets the lambda function assume my_role?

Do your buckets have bucket policies with deny statements? Also to confirm you're using Lambda not Lambda@Edge? — Chris Williams
– Chris Williams, Commented Jul 12, 2020 at 10:51
Have you also validated from the console that policies are attached as expected? — Chris Williams
– Chris Williams, Commented Jul 12, 2020 at 10:55
@ChrisWilliams No. But when I check via the browser I can see that the my_role is attached. However the permissions are not listed — User12547645
– User12547645, Commented Jul 12, 2020 at 11:02
@ChrisWilliams About the S3 Bucket: All policies seem normal. All public access blocked. No other deny statements — User12547645
– User12547645, Commented Jul 12, 2020 at 11:04
Right so this will be the cause, do you have the full code of you attaching this? I can't see any examples in this format — Chris Williams
– Chris Williams, Commented Jul 12, 2020 at 11:04

User12547645 · Accepted Answer · 2020-07-12 13:24:27Z

1

Solution: I was passing the wrong bucket name. The bucket name to an old account, which the function could (obviously) not access.

answered Jul 12, 2020 at 13:24

User12547645

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