walkthrough1

Walkthrough: Controlling Access to a Bucket with User Policies

This walkthrough explains how user permissions work with Amazon S3. In this example, you create a bucket with folders. You then create AWS Identity and Access Management (IAM) users in your AWS account and grant those users incremental permissions on your Amazon S3 bucket and the folders in it.

Topics

The Basics of Buckets and Folders

The Amazon S3 data model is a flat structure: You create a bucket, and the bucket stores objects. There is no hierarchy of subbuckets or subfolders, but you can emulate a folder hierarchy. Tools like the Amazon S3 console can present a view of these logical folders and subfolders in your bucket, as shown in the following image.

[Console screenshot showing a hierarchy of buckets, folders, and objects.]

The console shows that a bucket named companybucket has three folders, Private, Development, and Finance, and an object, s3-dg.pdf. The console uses the object names (keys) to create a logical hierarchy with folders and subfolders. Consider the following examples:

  • When you create the Development folder, the console creates an object with the key Development/. Note the trailing slash (/) delimiter.

  • When you upload an object named Projects1.xls in the Development folder, the console uploads the object and gives it the key Development/Projects1.xls.

    In the key, Development is the prefix and / is the delimiter. The Amazon S3 API supports prefixes and delimiters in its operations. For example, you can get a list of all objects from a bucket with a specific prefix and delimiter. On the console, when you open the Development folder, the console lists the objects in that folder. In the following example, the Development folder contains one object.

[Console screenshot showing a hierarchy of buckets, folders, and objects.]

When the console lists the Development folder in the companybucket bucket, it sends a request to Amazon S3 in which it specifies a prefix of Development and a delimiter of / in the request. The console's response looks just like a folder list in your computer's file system. The preceding example shows that the bucket companybucket has an object with the key Development/Projects1.xls.

The console is using object keys to infer a logical hierarchy. Amazon S3 has no physical hierarchy; it only has buckets that contain objects in a flat file structure. When you create objects using the Amazon S3 API, you can use object keys that imply a logical hierarchy. When you create a logical hierarchy of objects, you can manage access to individual folders, as this walkthrough demonstrates.

Before you start, be sure that you are familiar with the concept of the root-level bucket content. Suppose that your companybucket bucket has the following objects:

  • Private/privDoc1.txt
  • Private/privDoc2.zip
  • Development/project1.xls
  • Development/project2.xls
  • Finance/Tax2011/document1.pdf
  • Finance/Tax2011/document2.pdf
  • s3-dg.pdf

These object keys create a logical hierarchy with Private, Development, and the Finance as root-level folders and s3-dg.pdf as a root-level object. When you choose the bucket name on the Amazon S3 console, the root-level items appear as shown in the following image. The console shows the top-level prefixes (Private/, Development/, and Finance/) as root-level folders. The object key s3-dg.pdf has no prefix, and so it appears as a root-level item.

[Console screenshot of the objects tab with the s3-dg.pdf object in the list.]

Walkthrough Summary

In this walkthrough, you create a bucket with three folders (Private, Development, and Finance) in it.

You have two users, Alice and Bob. You want Alice to access only the Development folder, and you want Bob to access only the Finance folder. You want to keep the Private folder content private. In the walkthrough, you manage access by creating IAM users (the example uses the user names Alice and Bob) and granting them the necessary permissions.

IAM also supports creating user groups and granting group-level permissions that apply to all users in the group. This helps you better manage permissions. For this exercise, both Alice and Bob need some common permissions. So you also create a group named Consultants and then add both Alice and Bob to the group. You first grant permissions by attaching a group policy to the group. Then you add user-specific permissions by attaching policies to specific users.

Note
The walkthrough uses companybucket as the bucket name, Alice and Bob as the IAM users, and Consultants as the group name. Because Amazon S3 requires that bucket names be globally unique, you must replace the bucket name with a name that you create.

Preparing for the Walkthrough

In this example, you use your AWS account credentials to create IAM users. Initially, these users have no permissions. You incrementally grant these users permissions to perform specific Amazon S3 actions. To test these permissions, you sign in to the console with each user's credentials. As you incrementally grant permissions as an AWS account owner and test permissions as an IAM user, you need to sign in and out, each time using different credentials. You can do this testing with one browser, but the process will go faster if you can use two different browsers. Use one browser to connect to the AWS Management Console with your AWS account credentials and another to connect with the IAM user credentials.

To sign in to the AWS Management Console with your AWS account credentials, go to https://console.aws.amazon.com/. An IAM user cannot sign in using the same link. An IAM user must use an IAM-enabled sign-in page. As the account owner, you can provide this link to your users.

For more information about IAM, see The AWS Management Console Sign-in Page in the IAM User Guide.

To Provide a Sign-In Link for IAM Users

  1. Sign in to the AWS Management Console and open the IAM console at https://console.aws.amazon.com/iam/.

  2. In the Navigation pane, choose IAM Dashboard .

  3. Note the URL under IAM users sign in link:. You will give this link to IAM users to sign in to the console with their IAM user name and password.

Step 1: Create a Bucket

In this step, you sign in to the Amazon S3 console with your AWS account credentials, create a bucket, add folders (Development, Finance, and Private) to the bucket, and upload one or two sample documents in each folder.

  1. Sign in to the AWS Management Console and open the Amazon S3 console at https://console.aws.amazon.com/s3/.

  2. Create a bucket.

    For step-by-step instructions, see How Do I Create an S3 Bucket? in the Amazon Simple Storage Service Console User Guide.

  3. Upload one document to the bucket.

    This exercise assumes that you have the s3-dg.pdf document at the root level of this bucket. If you upload a different document, substitute its file name for s3-dg.pdf.

  4. Add three folders named Private, Finance, and Development to the bucket.

    For step-by-step instructions to create a folder, see Creating a Folder in the Amazon Simple Storage Service Console User Guide.

  5. Upload one or two documents to each folder.

    For this exercise, assume that you have uploaded a couple of documents in each folder, resulting in the bucket having objects with the following keys:

    • Private/privDoc1.txt
    • Private/privDoc2.zip
    • Development/project1.xls
    • Development/project2.xls
    • Finance/Tax2011/document1.pdf
    • Finance/Tax2011/document2.pdf
    • s3-dg.pdf

    For step-by-step instructions, see How Do I Upload Files and Folders to an S3 Bucket? in the Amazon Simple Storage Service Console User Guide.

Step 2: Create IAM Users and a Group

Now use the IAM console to add two IAM users, Alice and Bob, to your AWS account. Also create an administrative group named Consultants, and then add both users to the group.

Warning
When you add users and a group, do not attach any policies that grant permissions to these users. At first, these users don't have any permissions. In the following sections, you grant permissions incrementally. First you must ensure that you have assigned passwords to these IAM users. You use these user credentials to test Amazon S3 actions and verify that the permissions work as expected.

For step-by-step instructions for creating a new IAM user, see Creating an IAM User in Your AWS Account in the IAM User Guide. When you create the users for this walkthrough, select AWS Management Console access and clear Programmatic access.

For step-by-step instructions for creating an administrative group, see Creating Your First IAM Admin User and Group in the IAM User Guide.

Step 3: Verify That IAM Users Have No Permissions

If you are using two browsers, you can now use the second browser to sign in to the console using one of the IAM user credentials.

  1. Using the IAM user sign-in link (see To Provide a Sign-In Link for IAM Users), sign in to the AWS Management Console using either of the IAM user credentials.

  2. Open the Amazon S3 console at https://console.aws.amazon.com/s3/.

    Verify the following console message telling you that access is denied\.

    [Console screenshot showing an access denied error message.]

Now, you can begin granting incremental permissions to the users. First, you attach a group policy that grants permissions that both users must have.

Step 4: Grant Group-Level Permissions

You want the users to be able to do the following:

  • List all buckets owned by the parent account. To do so, Bob and Alice must have permission for the s3:ListAllMyBuckets action.
  • List root-level items, folders, and objects in the companybucket bucket. To do so, Bob and Alice must have permission for the s3:ListBucket action on the companybucket bucket.

First, you create a policy that grants these permissions, and then you attach it to the Consultants group.

Step 4.1: Grant Permission to List All Buckets

In this step, you create a managed policy that grants the users minimum permissions to enable them to list all buckets owned by the parent account. Then you attach the policy to the Consultants group. When you attach the managed policy to a user or a group, you grant the user or group permission to obtain a list of buckets owned by the parent AWS account.

  1. Sign in to the AWS Management Console and open the IAM console at https://console.aws.amazon.com/iam/. Note
    Because you are granting user permissions, sign in using your AWS account credentials, not as an IAM user.

  2. Create the managed policy.

    1. In the navigation pane on the left, choose Policies, and then choose Create Policy.

    2. Choose the JSON tab.

    3. Copy the following access policy and paste it into the policy text field.

      {
      "Version": "2012-10-17",
      "Statement": [
      {
      "Sid": "AllowGroupToSeeBucketListInTheConsole",
      "Action": ["s3:ListAllMyBuckets"],
      "Effect": "Allow",
      "Resource": ["arn:aws:s3:::*"]
      }
      ]
      }

      A policy is a JSON document. In the document, a Statement is an array of objects, each describing a permission using a collection of name-value pairs. The preceding policy describes one specific permission. The Action specifies the type of access. In the policy, the s3:ListAllMyBuckets is a predefined Amazon S3 action. This action covers the Amazon S3 GET Service operation, which returns list of all buckets owned by the authenticated sender. The Effect element value determines whether specific permission is allowed or denied.

    4. Choose Review Policy. On the next page, enter AllowGroupToSeeBucketListInTheConsole in the Name field, and then choose Create policy. Note
      The Summary entry displays a message stating that the policy does not grant any permissions. For this walkthrough, you can safely ignore this message.

  3. Attach the AllowGroupToSeeBucketListInTheConsole managed policy that you created to the Consultants group.

    For step-by-step instructions for attaching a managed policy, see Adding and Removing IAM Identity Permissions in the IAM User Guide.

    You attach policy documents to IAM users and groups in the IAM console. Because you want both users to be able to list the buckets, you attach the policy to the group.

  4. Test the permission.

    1. Using the IAM user sign-in link (see To Provide a Sign-In Link for IAM Users), sign in to the console using any one of IAM user credentials.

    2. Open the Amazon S3 console at https://console.aws.amazon.com/s3/.

      The console should now list all the buckets but not the objects in any of the buckets\.

      [Console screenshot showing a list of buckets.]

Step 4.2: Enable Users to List Root-Level Content of a Bucket

Next, you allow all users in the Consultants group to list the root-level companybucket bucket items. When a user chooses the company bucket on the Amazon S3 console, the user can see the root-level items in the bucket.

[Console screenshot showing the contents of companybucket.]

Note
This example uses companybucket for illustration. You must use the name of the bucket that you created.

To understand the request that the console sends to Amazon S3 when you choose a bucket name, the response that Amazon S3 returns, and how the console interprets the response, it is necessary to examine it a little more closely.

When you choose a bucket name, the console sends the GET Bucket (List Objects) request to Amazon S3. This request includes the following parameters:

  • The prefix parameter with an empty string as its value.
  • The delimiter parameter with / as its value.

The following is an example request.

GET ?prefix=&delimiter=/ HTTP/1.1
Host: companybucket.s3.amazonaws.com
Date: Wed, 01 Aug 2012 12:00:00 GMT
Authorization: AWS AKIAIOSFODNN7EXAMPLE:xQE0diMbLRepdf3YB+FIEXAMPLE=

Amazon S3 returns a response that includes the following <ListBucketResult/> element.

<ListBucketResult xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
<Name>companybucket</Name>
<Prefix></Prefix>
<Delimiter>/</Delimiter>
...
<Contents>
<Key>s3-dg.pdf</Key>
...
</Contents>
<CommonPrefixes>
<Prefix>Development/</Prefix>
</CommonPrefixes>
<CommonPrefixes>
<Prefix>Finance/</Prefix>
</CommonPrefixes>
<CommonPrefixes>
<Prefix>Private/</Prefix>
</CommonPrefixes>
</ListBucketResult>

The key s3-dg.pdf object does not contain the slash (/) delimiter, and Amazon S3 returns the key in the <Contents> element. However, all other keys in the example bucket contain the / delimiter. Amazon S3 groups these keys and returns a <CommonPrefixes> element for each of the distinct prefix values Development/, Finance/, and Private/ that is a substring from the beginning of these keys to the first occurrence of the specified / delimiter.

The console interprets this result and displays the root-level items as three folders and one object key.

[Console screenshot showing the contents of companybucket with three folders and one pdf file.]

If Bob or Alice opens the Development folder, the console sends the GET Bucket (List Objects) request to Amazon S3 with the prefix and the delimiter parameters set to the following values:

  • The prefix parameter with the value Development/.
  • The delimiter parameter with the "/" value.

In response, Amazon S3 returns the object keys that start with the specified prefix.

<ListBucketResult xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
<Name>companybucket</Name>
<Prefix>Development</Prefix>
<Delimiter>/</Delimiter>
...
<Contents>
<Key>Project1.xls</Key>
...
</Contents>
<Contents>
<Key>Project2.xls</Key>
...
</Contents>
</ListBucketResult>

The console shows the object keys.

[Console screenshot showing the development folder containing two xls files.]

Now, return to granting users permission to list the root-level bucket items. To list bucket content, users need permission to call the s3:ListBucket action, as shown in the following policy statement. To ensure that they see only the root-level content, you add a condition that users must specify an empty prefix in the request—that is, they are not allowed to double-click any of the root-level folders. Finally, you add a condition to require folder-style access by requiring user requests to include the delimiter parameter with the value "/".

{
"Sid": "AllowRootLevelListingOfCompanyBucket",
"Action": ["s3:ListBucket"],
"Effect": "Allow",
"Resource": ["arn:aws:s3:::companybucket"],
"Condition":{
"StringEquals":{
"s3:prefix":[""], "s3:delimiter":["/"]
}
}
}

When you choose a bucket on the Amazon S3 console, the console first sends the GET Bucket location request to find the AWS Region where the bucket is deployed. Then the console uses the Region-specific endpoint for the bucket to send the GET Bucket (List Objects) request. As a result, if users are going to use the console, you must grant permission for the s3:GetBucketLocation action as shown in the following policy statement.

{
"Sid": "RequiredByS3Console",
"Action": ["s3:GetBucketLocation"],
"Effect": "Allow",
"Resource": ["arn:aws:s3:::*"]
}

To enable users to list root-level bucket content

  1. Sign in to the AWS Management Console and open the Amazon S3 console at https://console.aws.amazon.com/s3/.

    Use your AWS account credentials, not the credentials of an IAM user, to sign in to the console.

  2. Replace the existing AllowGroupToSeeBucketListInTheConsole managed policy that is attached to the Consultants group with the following policy, which also allows the s3:ListBucket action. Remember to replace companybucket in the policy Resource with the name of your bucket.

    For step-by-step instructions, see Editing IAM Policies in the IAM User Guide. When following the step-by-step instructions, be sure to follow the steps for applying your changes to all principal entities that the policy is attached to.

    {
    "Version": "2012-10-17",
    "Statement": [
    {
    "Sid": "AllowGroupToSeeBucketListAndAlsoAllowGetBucketLocationRequiredForListBucket",
    "Action": [ "s3:ListAllMyBuckets", "s3:GetBucketLocation" ],
    "Effect": "Allow",
    "Resource": [ "arn:aws:s3:::*" ]
    },
    {
    "Sid": "AllowRootLevelListingOfCompanyBucket",
    "Action": ["s3:ListBucket"],
    "Effect": "Allow",
    "Resource": ["arn:aws:s3:::companybucket"],
    "Condition":{
    "StringEquals":{
    "s3:prefix":[""], "s3:delimiter":["/"]
    }
    }
    }
    ]
    }

  3. Test the updated permissions.

    1. Using the IAM user sign-in link (see To Provide a Sign-In Link for IAM Users), sign in to the AWS Management Console.

      Open the Amazon S3 console at https://console.aws.amazon.com/s3/.

    2. Choose the bucket that you created, and the console shows the root-level bucket items. If you choose any folders in the bucket, you won't be able to see the folder content because you haven't yet granted those permissions.
      [Console screenshot showing the company bucket containing three folders.]

This test succeeds when users use the Amazon S3 console. When you choose a bucket on the console, the console implementation sends a request that includes the prefix parameter with an empty string as its value and the delimiter parameter with "/" as its value.

Step 4.3: Summary of the Group Policy

The net effect of the group policy that you added is to grant the IAM users Alice and Bob the following minimum permissions:

  • List all buckets owned by the parent account.
  • See root-level items in the companybucket bucket.

However, the users still can't do much. Next, you grant user-specific permissions, as follows:

  • Allow Alice to get and put objects in the Development folder.
  • Allow Bob to get and put objects in the Finance folder.

For user-specific permissions, you attach a policy to the specific user, not to the group. In the following section, you grant Alice permission to work in the Development folder. You can repeat the steps to grant similar permission to Bob to work in the Finance folder.

Step 5: Grant IAM User Alice Specific Permissions

Now you grant additional permissions to Alice so that she can see the content of the Development folder and get and put objects in that folder.

Step 5.1: Grant IAM User Alice Permission to List the Development Folder Content

For Alice to list the Development folder content, you must apply a policy to the Alice user that grants permission for the s3:ListBucket action on the companybucket bucket, provided the request includes the prefix Development/. You want this policy to be applied only to the user Alice, so you use an inline policy. For more information about inline policies, see Managed Policies and Inline Policies in the IAM User Guide.

  1. Sign in to the AWS Management Console and open the IAM console at https://console.aws.amazon.com/iam/.

    Use your AWS account credentials, not the credentials of an IAM user, to sign in to the console.

  2. Create an inline policy to grant the user Alice permission to list the Development folder content.

    1. In the navigation pane on the left, choose Users.

    2. Choose the user name Alice.

    3. On the user details page, choose the Permissions tab and then choose Add inline policy.

    4. Choose the JSON tab.

    5. Copy the following policy and paste it into the policy text field.

      {
      "Version": "2012-10-17",
      "Statement": [
      {
      "Sid": "AllowListBucketIfSpecificPrefixIsIncludedInRequest",
      "Action": ["s3:ListBucket"],
      "Effect": "Allow",
      "Resource": ["arn:aws:s3:::companybucket"],
      "Condition":{ "StringLike":{"s3:prefix":["Development/*"] }
      }
      }
      ]
      }

    6. Choose Review Policy. On the next page, enter a name in the Name field, and then choose Create policy.

  3. Test the change to Alice's permissions:

    1. Using the IAM user sign-in link (see To Provide a Sign-In Link for IAM Users), sign in to the AWS Management Console.

    2. Open the Amazon S3 console at https://console.aws.amazon.com/s3/.

    3. On the Amazon S3 console, verify that Alice can see the list of objects in the Development/ folder in the bucket.

      When the user chooses the `/Development` folder to see the list of objects in it, the Amazon S3 console sends the `ListObjects` request to Amazon S3 with the prefix `/Development`\. Because the user is granted permission to see the object list with the prefix `Development` and delimiter `/`, Amazon S3 returns the list of objects with the key prefix `Development/`, and the console displays the list\.

      [Console screenshot showing the development folder containing two xls files.]

Step 5.2: Grant IAM User Alice Permissions to Get and Put Objects in the Development Folder

For Alice to get and put objects in the Development folder, she needs permission to call the s3:GetObject and s3:PutObject actions. The following policy statements grant these permissions, provided that the request includes the prefix parameter with a value of Development/.

{
"Sid":"AllowUserToReadWriteObjectData",
"Action":["s3:GetObject", "s3:PutObject"],
"Effect":"Allow",
"Resource":["arn:aws:s3:::companybucket/Development/*"]
}

  1. Sign in to the AWS Management Console and open the Amazon S3 console at https://console.aws.amazon.com/s3/.

    Use your AWS account credentials, not the credentials of an IAM user, to sign in to the console.

  2. Edit the inline policy that you created in the previous step.

    1. In the navigation pane on the left, choose Users.

    2. Choose the user name Alice.

    3. On the user details page, choose the Permissions tab and expand the Inline Policies section.

    4. Next to the name of the policy that you created in the previous step, choose Edit Policy.

    5. Copy the following policy and paste it into the policy text field, replacing the existing policy.

      {
      "Version": "2012-10-17",
      "Statement":[
      {
      "Sid":"AllowListBucketIfSpecificPrefixIsIncludedInRequest",
      "Action":["s3:ListBucket"],
      "Effect":"Allow",
      "Resource":["arn:aws:s3:::companybucket"],
      "Condition":{
      "StringLike":{"s3:prefix":["Development/*"]
      }
      }
      },
      {
      "Sid":"AllowUserToReadWriteObjectDataInDevelopmentFolder",
      "Action":["s3:GetObject", "s3:PutObject"],
      "Effect":"Allow",
      "Resource":["arn:aws:s3:::companybucket/Development/*"]
      }
      ]
      }

  3. Test the updated policy:

    1. Using the IAM user sign-in link (see To Provide a Sign-In Link for IAM Users), sign into the AWS Management Console.

    2. Open the Amazon S3 console at https://console.aws.amazon.com/s3/.

    3. On the Amazon S3 console, verify that Alice can now add an object and download an object in the Development folder.

Step 5.3: Explicitly Deny IAM User Alice Permissions to Any Other Folders in the Bucket

User Alice can now list the root-level content in the companybucket bucket. She can also get and put objects in the Development folder. If you really want to tighten the access permissions, you could explicitly deny Alice access to any other folders in the bucket. If there is any other policy (bucket policy or ACL) that grants Alice access to any other folders in the bucket, this explicit deny overrides those permissions.

You can add the following statement to the user Alice policy that requires all requests that Alice sends to Amazon S3 to include the prefix parameter, whose value can be either Development/* or an empty string.

{
"Sid": "ExplicitlyDenyAnyRequestsForAllOtherFoldersExceptDevelopment",
"Action": ["s3:ListBucket"],
"Effect": "Deny",
"Resource": ["arn:aws:s3:::companybucket"],
"Condition":{ "StringNotLike": {"s3:prefix":["Development/*",""] },
"Null" : {"s3:prefix":false }
}
}

There are two conditional expressions in the Condition block. The result of these conditional expressions is combined by using the logical AND. If both conditions are true, the result of the combined condition is true. Because the Effect in this policy is Deny, when the Condition evaluates to true, users can't perform the specified Action.

  • The Null conditional expression ensures that requests from Alice include the prefix parameter.

    The prefix parameter requires folder-like access. If you send a request without the prefix parameter, Amazon S3 returns all the object keys.

    If the request includes the prefix parameter with a null value, the expression evaluates to true, and so the entire Condition evaluates to true. You must allow an empty string as value of the prefix parameter. From the preceding discussion, recall that allowing the null string allows Alice to retrieve root-level bucket items as the console does in the preceding discussion. For more information, see Step 4.2: Enable Users to List Root-Level Content of a Bucket.

  • The StringNotLike conditional expression ensures that if the value of the prefix parameter is specified and is not Development/*, the request fails.

Follow the steps in the preceding section and again update the inline policy that you created for user Alice.

Copy the following policy and paste it into the policy text field, replacing the existing policy.

{
"Version": "2012-10-17",
"Statement":[
{
"Sid":"AllowListBucketIfSpecificPrefixIsIncludedInRequest",
"Action":["s3:ListBucket"],
"Effect":"Allow",
"Resource":["arn:aws:s3:::companybucket"],
"Condition":{
"StringLike":{"s3:prefix":["Development/*"]
}
}
},
{
"Sid":"AllowUserToReadWriteObjectDataInDevelopmentFolder",
"Action":["s3:GetObject", "s3:PutObject"],
"Effect":"Allow",
"Resource":["arn:aws:s3:::companybucket/Development/*"]
},
{
"Sid": "ExplicitlyDenyAnyRequestsForAllOtherFoldersExceptDevelopment",
"Action": ["s3:ListBucket"],
"Effect": "Deny",
"Resource": ["arn:aws:s3:::companybucket"],
"Condition":{ "StringNotLike": {"s3:prefix":["Development/*",""] },
"Null" : {"s3:prefix":false }
}
}
]
}

Step 6: Grant IAM User Bob Specific Permissions

Now you want to grant Bob permission to the Finance folder. Follow the steps that you used earlier to grant permissions to Alice, but replace the Development folder with the Finance folder. For step-by-step instructions, see Step 5: Grant IAM User Alice Specific Permissions.

Step 7: Secure the Private Folder

In this example, you have only two users. You granted all the minimum required permissions at the group level and granted user-level permissions only when you really need to permissions at the individual user level. This approach helps minimize the effort of managing permissions. As the number of users increases, managing permissions can become cumbersome. For example, you don't want any of the users in this example to access the content of the Private folder. How do you ensure that you don't accidentally grant a user permission to it? You add a policy that explicitly denies access to the folder. An explicit deny overrides any other permissions.

To ensure that the Private folder remains private, you can add the following two deny statements to the group policy:

  • Add the following statement to explicitly deny any action on resources in the Private folder (companybucket/Private/*).

    {
    "Sid": "ExplictDenyAccessToPrivateFolderToEveryoneInTheGroup",
    "Action": ["s3:*"],
    "Effect": "Deny",
    "Resource":["arn:aws:s3:::companybucket/Private/*"]
    }

  • You also deny permission for the list objects action when the request specifies the Private/ prefix. On the console, if Bob or Alice opens the Private folder, this policy causes Amazon S3 to return an error response.

    {
    "Sid": "DenyListBucketOnPrivateFolder",
    "Action": ["s3:ListBucket"],
    "Effect": "Deny",
    "Resource": ["arn:aws:s3:::*"],
    "Condition":{
    "StringLike":{"s3:prefix":["Private/"]}
    }
    }

Replace the Consultants group policy with an updated policy that includes the preceding deny statements. After the updated policy is applied, none of the users in the group can access the Private folder in your bucket.

  1. Sign in to the AWS Management Console and open the Amazon S3 console at https://console.aws.amazon.com/s3/.

    Use your AWS account credentials, not the credentials of an IAM user, to sign in to the console.

  2. Replace the existing AllowGroupToSeeBucketListInTheConsole managed policy that is attached to the Consultants group with the following policy. Remember to replace companybucket in the policy with the name of your bucket.

    For instructions, see Editing Customer Managed Policies in the IAM User Guide. When following the instructions, make sure to follow the directions for applying your changes to all principal entities that the policy is attached to.

    {
    "Version": "2012-10-17",
    "Statement": [
    {
    "Sid": "AllowGroupToSeeBucketListAndAlsoAllowGetBucketLocationRequiredForListBucket",
    "Action": ["s3:ListAllMyBuckets", "s3:GetBucketLocation"],
    "Effect": "Allow",
    "Resource": ["arn:aws:s3:::*"]
    },
    {
    "Sid": "AllowRootLevelListingOfCompanyBucket",
    "Action": ["s3:ListBucket"],
    "Effect": "Allow",
    "Resource": ["arn:aws:s3:::companybucket"],
    "Condition":{
    "StringEquals":{"s3:prefix":[""]}
    }
    },
    {
    "Sid": "RequireFolderStyleList",
    "Action": ["s3:ListBucket"],
    "Effect": "Deny",
    "Resource": ["arn:aws:s3:::*"],
    "Condition":{
    "StringNotEquals":{"s3:delimiter":"/"}
    }
    },
    {
    "Sid": "ExplictDenyAccessToPrivateFolderToEveryoneInTheGroup",
    "Action": ["s3:*"],
    "Effect": "Deny",
    "Resource":["arn:aws:s3:::companybucket/Private/*"]
    },
    {
    "Sid": "DenyListBucketOnPrivateFolder",
    "Action": ["s3:ListBucket"],
    "Effect": "Deny",
    "Resource": ["arn:aws:s3:::*"],
    "Condition":{
    "StringLike":{"s3:prefix":["Private/"]}
    }
    }
    ]
    }

Step 8: Clean Up

To clean up, open the IAM console and remove the users Alice and Bob. For step-by-step instructions, see Deleting an IAM User in the IAM User Guide.

To ensure that you aren't charged further for storage, you should also delete the objects and the bucket that you created for this exercise.

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