Designing resource policies to restrict access to authorized users (for example, S3 bucket policies, DynamoDB policies)

What is the difference between an IAM policy and a resource-based policy?

An IAM policy is attached to IAM users, groups, or roles in AWS and defines the permissions those identities have. In contrast, a resource-based policy is attached directly to a specific AWS resource, such as an S3 bucket or a DynamoDB table, and specifies who has access to that resource and what actions they can perform on it.

Can you explain what an S3 bucket policy is and how it helps in restricting access?

An S3 bucket policy is a type of resource-based policy, written in JSON, that you attach to an Amazon S3 bucket. It defines the permissions for who can access the S3 bucket and what actions they can perform, such as put, get, or delete objects. This helps in ensuring that only authorized users or services can access or manipulate the data stored in the S3 bucket.

When would you choose to use a bucket policy over an IAM policy for controlling access to S3 buckets?

You would choose to use a bucket policy over an IAM policy when you want to manage permissions at the bucket level rather than at the user or group level. This is especially useful for granting access to users from other AWS accounts or when managing permissions for multiple buckets in a consistent manner.

Describe a scenario where you need to restrict access to a DynamoDB table using a policy.

A common scenario would be if you want to restrict access so only certain IAM users or roles within your AWS account can read data from or write data to a DynamoDB table. Additionally, you might want to restrict certain actions based on conditions, such as limiting write access only to a specific IP address range or during certain times of the day.

What is the role of condition operators in IAM policies?

Condition operators in IAM policies allow you to specify conditions for when a policy is in effect. For example, you can use “IpAddress” to restrict access to a resource only from certain IP addresses, or “DateGreaterThan” to only allow access after a certain date. This enables finer-grained access control and can enhance the security by limiting how and when a resource can be accessed.

How would you grant access to specific folders within an S3 bucket?

You would use the “Resource” element in an S3 bucket policy to specify the ARNs (Amazon Resource Names) of the bucket and the particular folder paths you want to allow access to. Using the “StringLike” condition with the “s3:prefix” key allows you to match folder names.

How do you ensure a policy allows access to an S3 bucket only if the request is made over a secure connection (HTTPS)?

In your bucket policy, you can use a condition to enforce access only over SSL by including the “aws:SecureTransport” key with a value of “true.” This will deny any request made over an unsecured connection (HTTP).

Explain how to provide cross-account access to an S3 bucket using bucket policies.

To provide cross-account access, you need to specify the AWS account ID of the external account in the “Principal” element of your S3 bucket policy. You also define the actions and resources that the external account can access.

What are best practices when creating resource policies for access control?

Best practices include following the principle of least privilege (granting the minimal permissions necessary), regularly reviewing and updating policies, avoiding the use of wildcard actions or principals unless absolutely necessary, using condition clauses to restrict access, and incorporating logging and monitoring to track access.

Can you use resource tags to control access to S3 buckets or DynamoDB tables?

Yes, you can include tags in a policy condition to control access to resources. For example, you can use the “aws:RequestTag/your-tag-key” condition key to restrict write access to an S3 bucket or a DynamoDB table only if the request includes a specific tag.

How can you automatically deny all unencrypted requests to an S3 bucket?

You can create a bucket policy with a condition that denies any S3 operation when the request lacks the necessary encryption headers, such as “x-amz-server-side-encryption” for server-side encryption with AWS KMS keys.

If an IAM user needs to temporarily access a DynamoDB table with increased permissions, how would you securely manage this?

You would use IAM roles with temporary security credentials for assuming the required role with increased permissions. When the task is completed, you can revoke the role or let the temporary credentials expire to automatically reduce permissions.