S3 Object Storage - Bucket Policy

Bucket Policy Overview

Bucket Policy is a resource-based policy option. It allows users to grant access to buckets to other Scaleway projects and organizations.

By default, all S3 resources in a project are private and can be accessed only by users of the project. To grant access to outside users, a policy file can be added to a bucket via an API call or the AWS-CLI.

Note: Bucket policies use a JSON-based access policy language. You can find more details about the JSON policy grammar on this page.

In this documentation, you will learn how to:

Requirements

You have:

PUT Bucket Policy

This operation applies an S3 bucket policy to an S3 bucket.

Sample API Request:

PUT /myBucket?policy HTTP/1.1
{
    "Version": "2012-10-17",
    "Id": "MyBucketPolicy",
    "Statement": [
        {
            "Sid": "DelegateAccess",
            "Effect": "Allow",
            "Principal":{
                "SCW": "project_id:<PROJECT_ID>"
            },
            "Action": [
                "s3:ListBucket",
                "s3:GetObject"
            ],
            "Resource": [
                "<BUCKET_NAME>",
                "<BUCKET_NAME>/*"
            ]
        }
    ]
}

AWS-CLI Command:

Create the file bucket-policy.json with the following content:

{
    "Version": "2012-10-17",
    "Id": "Mybucketpolicy",
    "Statement": [
        {
            "Sid": "DelegateAccess",
            "Effect": "Allow",
            "Principal": {
                "SCW": "project_id:<PROJECT_ID>"
            },
            "Action": [
                "s3:ListBucket",
                "s3:GetObject"
            ],
            "Resource": [
                "<BUCKET_NAME>",
                "<BUCKET_NAME>/*"
            ]
        }
    ]
}

Then run the following command:

$ aws s3api put-bucket-policy --bucket <BUCKET_NAME> --policy file://bucket-policy.json

GET Bucket Policy

This operation returns the policy of a specified bucket.

Sample API Request:

GET /myBucket?policy HTTP/1.1

Sample API Output:

{
    "Policy": "{\"Version\": \"2012-10-17\", \"Statement\": [{\"Action\": [\"s3:GetObject\"], \"Principal\": {\"SCW\": [\"<PROJECT_ID>\"]}, \"Resource\": [\"myBucket/*\"], \"Effect\": \"Allow\", \"Sid\": \"DelegateGetObject\"}]}"
}

AWS-CLI Command:

$ aws s3api get-bucket-policy --bucket myBucket
{
    "Policy": "{\"Version\": \"2012-10-17\", \"Statement\": [{\"Action\": [\"s3:GetObject\"], \"Principal\": {\"SCW\": [\"<PROJECT_ID>\"]}, \"Resource\": [\"myBucket/*\"], \"Effect\": \"Allow\", \"Sid\": \"DelegateGetObject\"}]}"
}

DELETE Bucket Policy

This operation deletes the Bucket Policy of a specified bucket.

If the operation is successful, no output will be returned.

Sample API Request:

DELETE /MyBucket?policy HTTP/1.1

AWS-CLI Command:

$ aws s3api delete-bucket-policy --bucket myBucket -> code block

How to share buckets in read-only mode

You can implement a Bucket Policy to grant a Scaleway organization or project viewing rights to a bucket in a different project.

For example, you are logged in to Organization A and you have a bucket (A1) inside Project A. You wish to share the bucket in read-only mode with users in Organization B, Project B.

To do so, you have to apply a policy to bucket A1 that grants access to Organization B or Project B and include which API calls they are allowed to make.

To guarantee that they can only view contents, include "s3:ListBucket" and "s3:GetObject" under Action in the bucket-policy.json file you create.

Specify which resources they can access under Resource:

  • "<BUCKET_NAME>" - Grants access to the bucket, but not to the objects inside. If the s3:ListBucket action is applied, this resource specification is required.
  • "<BUCKET_NAME>/*" - Grants access to all objects inside a bucket, but not to the bucket itself. If the s3:GetObject actions is applied, this resource specification is required.
  • "<BUCKET_NAME>/<PREFIX>/*" - Grants access only to objects with the specified prefix inside a bucket, but not to the bucket itself. For example, if you apply a bucket policy that specifies "my_files/movie/*" under Resource, you would grant access to all objects with the movie/ prefix, but not to other objects in my_files/ bucket. If the s3:GetObject actions is applied, this resource specification is required.
{
    "Version": "2012-10-17",
    "Id": "Mybucketpolicy",
    "Statement": [
        {
            "Sid": "DelegateAccess",
            "Effect": "Allow",
            "Principal": {
                "SCW": "project_id:<PROJECT_ID>"
            },
            "Action": [
                "s3:ListBucket",
                "s3:GetObject"
            ],
            "Resource": [
                "<BUCKET_NAME>",
                "<BUCKET_NAME>/*"
            ]
        }
    ]
}

Apply the policy using the Put Bucket Policy API call or run the aws-cli command.

$ aws s3api put-bucket-policy --bucket <SOURCE_BUCKET> --profile default_project --policy file://bucket-policy.json

You can provide the user in Organization B the name of your bucket. If the policy is correctly applied, they will be able to see bucket A1 included in their bucket list when running List_Buckets. If they know the name of an object, they can view their details by running Get_Object.

How to import a copy of objects from a bucket in a different project

To import a copy of objects in a bucket to another bucket in a different project, you need to implement a Bucket Policy. Find the detailed step-by-step in this documentation page.

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