Understanding bucket policies

Reviewed on 29 December 2021 • Published on 17 February 2021

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

By default, all Object Storage resources in a project are private and can be accessed only by users of said project. Adding a bucket policy to a bucket allows you to grant access to outside users. You can use different combinations of the policy’s component strings to customize your permissions for different purposes as required.

Bucket policies use a JSON-based access policy language and are composed of strings, such as: Version, Id, Statement, Sid, Principal, Action, Effect, Resource and Condition.

Version

Description: IAM syntax version
Required: Yes
Type: const
Value: “2012-10-17”

Sample:

{
    "Version": "2012-10-17",
    "Id": "MyBucketPolicy",
    "Statement": [
        {
            "Sid": "Delegate access",
            "Effect":"Allow",
            "Principal": {
                "SCW": "project_id:<PROJECT_ID>"
            },
            "Action": "s3:ListBucket",
            "Resource": "<BUCKET_NAME>"
        }
    ]
}

Id

Description: Information about the policy as a whole. The length is limited to 280 characters.
Required: No
Type: string

Sample

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

Statement

Description: Statement is an array that defines the rules that should be respected by our policy engine.
Children: Sid, Principal, Action, Effect and Resource
Required: No
Type: array

Samples

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

{    
    "Version": "2012-10-17",
    "Id":"MyBucketPolicy",
    "Statement": [
        {
            "Sid": "Delegate access to project",
            "Effect":"Allow",
            "Principal":{
                "SCW":"project_id:<PROJECT_ID>"
            },
            "Action":[
                "s3:ListBucket",
                "s3:GetObject"
            ],
            "Resource":[
                "<BUCKET_NAME>",
                "<BUCKET_NAME>/*"
            ]
        },
        {
            "Sid": "Delegate PUT to project bis",
            "Effect":"Allow",
            "Principal":{
                "SCW":"project_id:<PROJECT_ID_BIS>"
            },
            "Action":"s3:PutObject",
            "Resource":"<BUCKET_NAME>/*"
        }
    ]
}

Sid

Description: Provides a way to include information about an individual statement.
Required: No
Parent: Statement
Type: string

Sample

{
    "Version": "2012-10-17",
    "Id":"MyBucketPolicy",
    "Statement": [
        {
            "Sid": "Grant list to <PROJECT_ID>",
            "Effect":"Allow",
            "Principal":{
                "SCW":"project_id:<PROJECT_ID>"
            },
            "Action":"s3:ListBucket",
            "Resource":"<BUCKET_NAME>"
        }
    ]
}

Principal

Description: Provides a way to specify a principal using the ProjectID of a Scaleway Project. Note that you can use * to grant access to “everyone”.
Required: Yes
Parent: Statement

Sample

{
    "Version": "2012-10-17",
    "Id":"MyBucketPolicy",
    "Statement": [
        {
            "Sid": "Grant List and GET to everyone",
            "Effect":"Allow",
            "Principal":"*",
            "Action":[
                "s3:ListBucket",
                "s3:GetObject"
            ],
            "Resource":[
                "<BUCKET_NAME>",
                "<BUCKET_NAME>/*"
            ]
        }
    ]
}

{
    "Version": "2012-10-17",
    "Id":"MyBucketPolicy",
    "Statement": [
        {
            "Sid": "Grant List and GET to <PROJECT_ID>",
            "Effect":"Allow",
            "Principal":{
                "SCW":"project_id:<PROJECT_ID>"
            },
            "Action":[
                "s3:ListBucket",
                "s3:GetObject"
            ],
            "Resource":[
                "<BUCKET_NAME>",
                "<BUCKET_NAME>/*"
            ]
        }
    ]
}

{
    "Version": "2012-10-17",
    "Id":"MyBucketPolicy",
    "Statement": [
        {
            "Sid": "Grant List and GET to <PROJECT_ID> and < PROJECT_ID_BIS>",
            "Effect":"Allow",
            "Principal":{
                "SCW":[
                    "project_id:<PROJECT_ID>",
                    "project_id:<PROJECT_ID_BIS>"
                ]
            },
            "Action":[
                "s3:ListBucket",
                "s3:GetObject"
            ],
            "Resource":[
                "<BUCKET_NAME>",
                "<BUCKET_NAME>/*"
            ]
        }
    ]
}

Action

Description: Consists of S3 namespace, a colon, and the name of an action. Action names can include wildcards represented by *.
Required: Yes
Parent: Statement

Sample

{
    "Version": "2012-10-17",
    "Id":"MyBucketPolicy",
    "Statement": [
        {
            "Sid": "Grant List and GET to <PROJECT_ID> and < PROJECT_ID_BIS>",
            "Effect":"Allow",
            "Principal":{
                "SCW":[
                    "project_id:<PROJECT_ID>",
                    "project_id:<PROJECT_ID_BIS>"
                ]
            },
            "Action":"*",
            "Resource":[
                "<BUCKET_NAME>",
                "<BUCKET_NAME>/*"
            ]
        }
    ]
}

Supported actions

*
s3:*
s3:AbortMultipartUpload
s3:DeleteBucketWebsite
s3:DeleteObject
s3:DeleteObjectTagging
s3:DeleteObjectVersion
s3:DeleteObjectVersionTagging
s3:GetBucketTagging
s3:GetBucketVersioning
s3:GetBucketWebsite
s3:GetLifecycleConfiguration
s3:GetObject
s3:GetObjectTagging
s3:GetObjectVersion
s3:GetObjectVersionTagging
s3:ListBucket
s3:ListBucketMultipartUploads
s3:ListMultipartUploadParts
s3:PutBucketTagging
s3:PutBucketVersioning
s3:PutBucketWebsite
s3:PutLifecycleConfiguration
s3:PutObject
s3:PutObjectTagging
s3:PutObjectVersionTagging

Effect

Description: Uses Allow or Deny to indicate whether the policy allows or denies access.
Required: Yes
Parent: Statement

Sample

Allow

{
    "Version": "2012-10-17",
    "Id":"MyBucketPolicy",
    "Statement": [
        {
            "Sid": "Grant List and GET to <PROJECT_ID> and <PROJECT_ID_BIS>",
            "Effect":"Allow",
            "Principal":{
                "SCW":[
                    "project_id:<PROJECT_ID>",
                    "project_id:<PROJECT_ID_BIS>"
                ]
            },
            "Action":[
                "s3:ListBucket",
                "s3:GetObject"
            ],
            "Resource":[
                "<BUCKET_NAME>",
                "<BUCKET_NAME>/*"
            ]
        }
    ]
}

Deny

{
  "Version": "2012-10-17",
  "Id": "MyBucketPolicy",
  "Statement": [
    {
      "Sid": "Deny DELETE to everyone",
      "Effect": "Deny",
      "Principal": "*",
      "Action": "s3:DeleteObject",
      "Resource": "*"
    }
  ]
}

Resource

Description: Consists in the S3 resource path.
Required: Yes
Parent: Statement

Sample

"<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:PutObject, s3:GetObject and s3:DeleteObject actions are 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:PutObject, s3:GetObject and s3:DeleteObject actions are applied, this resource specification is required.

{
    "Version": "2012-10-17",
    "Id":"MyBucketPolicy",
    "Statement": [
        {
            "Sid": "Grant List and GET to <PROJECT_ID> and < PROJECT_ID_BIS>",
            "Effect":"Allow",
            "Principal":{
                "SCW":[
                    "project_id:<PROJECT_ID>",
                    "project_id:<PROJECT_ID_BIS>"
                ]
            },
            "Action":[
                "s3:ListBucket",
                "s3:GetObject"
            ],
            "Resource":[
                "<BUCKET_NAME>",
                "<BUCKET_NAME>/*"
            ]
        }
    ]
}

{
    "Version": "2012-10-17",
    "Id":"MyBucketPolicy",
    "Statement": [
        {
            "Sid": "Grant List and GET to <PROJECT_ID> and < PROJECT_ID_BIS>",
            "Effect":"Allow",
            "Principal":{
                "SCW":[
                    "project_id:<PROJECT_ID>",
                    "project_id:<PROJECT_ID_BIS>"
                ]
            },
            "Action":[
                "s3:ListBucket",
                "s3:GetObject"
            ],
            "Resource":[
                "<BUCKET_NAME>",
                "<BUCKET_NAME>/photos/*"
            ]
        }
    ]
}

Condition

Description: The Condition element allows you specify conditions for when a Policy is in effect.
Required: No
Parent: Statement
Condition Keys: aws:SourceIp, aws:Referer, aws:CurrentTime, aws:EpochTime

Examples

You can use the IpAddress condition to Allow actions for specific IP ranges or addresses.

{
  "Version": "2012-10-17",
  "Id": "MyBucketPolicy",
  "Statement": [
    {
      "Sid": "Grant List and GET from my Instances",
      "Effect": "Allow",
      "Principal": "*",
      "Action": ["s3:ListBucket", "s3:GetObject"],
      "Resource": ["<BUCKET_NAME>", "<BUCKET_NAME>/*"],
      "Condition": {
        "IpAddress": {
          "aws:SourceIp": "192.0.2.0/24"
        }
      }
    }
  ]
}

You can allow access only within a set timeframe, by implementing the DateGreaterThan and DateLessThan conditions.

{
  "Version": "2012-10-17",
  "Id": "MyBucketPolicy",
  "Statement": [
    {
      "Sid": "Grant List and GET to <PROJECT_ID> for 10 years",
      "Effect": "Allow",
      "Principal": {
        "SCW": "project_id:<PROJECT_ID>"
      },
      "Action": ["s3:ListBucket", "s3:GetObject"],
      "Resource": ["<BUCKET_NAME>", "<BUCKET_NAME>/photos/*"],
      "Condition": {
        "DateGreaterThan": {
          "aws:CurrentTime": "2020-01-01T00:00:00Z"
        },
        "DateLessThan": {
          "aws:CurrentTime": "2030-01-01T00:00:00Z"
        }
      }
    }
  ]
}

You can also allow access according to the HTTP referer.

{
  "Version": "2012-10-17",
  "Id": "MyBucketPolicy",
  "Statement": [
    {
      "Sid": "Allow access to assets from my website",
      "Effect": "Allow",
      "Principal": "*",
      "Action": "s3:GetObject",
      "Resource": ["<BUCKET_NAME>/assets/*"],
      "Condition": {
        "StringLike": {
          "aws:Referer": "https://console.scaleway.com"
        }
      }
    }
  ]
}

Supported conditions

IpAddress
NotIpAddress
StringEquals
StringNotEquals
StringEqualsIgnoreCase
StringNotEqualsIgnoreCase
StringLike
StringNotLike
DateGreaterThan
DateGreaterThanEquals
DateLessThan
DateLessThanEquals