AWS S3 Bucket Policy to allow only lowercase files

Question

Is it possible to limit s3 bucket to lowercase files/directories only?

Some downstream systems are case insensitive so I want to prevent any issues.

There's a Lambda workaround, but is it possible to specify this requirement as a bucket policy?

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Enforce lower-case",
            "Effect": "Deny",
            "Principal":"*",
            "Action": "s3:PutObject",
            "Resource": "arn:aws:s3:::mybucket/*",
            "Condition": {
                "StringNotEquals": {
                    "s3:KeyName": "lower(s3:KeyName)"
                }
            }
        }
    ]
}

This isn't possible. The `StringLike`/`StringNotLike` wildcards are fairly simple, you can't create a full Regex-like expression. — Anon Coward, Nov 17 '22 at 19:57

score 3 · Accepted Answer · answered Nov 17 '22 at 19:59

3

No, that is not possible because:

String manipulation isn't allowed in IAM policy
IAM string condition operators do not support regular expressions

answered Nov 17 '22 at 19:59

Paolo

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score 1 · Answer 2 · answered Nov 17 '22 at 20:26

1

An alternative approach would be to have the S3 bucket trigger an AWS Lambda function, which could:

Examine the object Key
If the Key is not strictly lowercase, then Copy the object to a new lowercase Key and delete the original object

However, it would mean that Foo would rename to foo and a later FOO would overwrite foo.

answered Nov 17 '22 at 20:26

John Rotenstein

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This doesn't answer the question. Also, OP is already aware of the lambda workaround. – Paolo Nov 17 '22 at 21:26

AWS S3 Bucket Policy to allow only lowercase files

2 Answers2