# Cross-account access

It is often desirable to run the Quilt control plane (CloudFormation stack) in a separate account from your data plane (S3 buckets).

Assume that we have two accounts, *ControlAccount* (containing the Quilt CloudFormation stack) and *DataAccount* (containing the desired S3 buckets).

## Object ownership

If you want *DataAccount* to have access to S3 objects put by *ControlAccount* (and you probably do), you need to ensure that S3 bucket has `ObjectOwnership` set to `BucketOwnerEnforced`, see [docs](https://docs.aws.amazon.com/AmazonS3/latest/userguide/about-object-ownership.html) for details.

## Bucket policies

To ensure that the Quilt stack in the *ControlAccount* can access and administer S3 buckets in the *DataAccount*, you can apply a bucket policy similar to the following to buckets in your *DataAccount*.

> Quilt admins can still control which users do and do not have access to the following bucket via Admin panel Roles and Policies.

```json
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::CONTROL_ACCOUNT:root"
            },
            "Action": [
                "s3:GetObject",
                "s3:GetObjectVersion",
                "s3:ListBucket",
                "s3:ListBucketVersions",
                "s3:DeleteObject",
                "s3:DeleteObjectVersion",
                "s3:PutObject",
                "s3:GetBucketNotification",
                "s3:PutBucketNotification"
            ],
            "Resource": [
                "arn:aws:s3:::bucket-in-data-account",
                "arn:aws:s3:::bucket-in-data-account/*"
            ]
        }
    ]
}
```

## CloudTrail

For security, auditing, and user-facing analytics, it is recommended that all S3 buckets in Quilt enable logging via CloudTrail. For cross-account buckets you must provide an existing trail to Quilt when you deploy the CloudFormation template, and you must add the buckets in question to CloudTrail.


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