Tutorial / Cram Notes

Identity and Access Management (IAM) roles can be assumed by users, applications, or services from another AWS account. By creating a role with precise permissions and allowing a trusted external AWS account to assume this role, you provide access to the resources without sharing the actual access keys.

For example, to allow users from Account B to access an S3 bucket in Account A, you would:

  1. Create an IAM policy in Account A that defines the necessary permissions on the S3 bucket.
  2. Create an IAM role in Account A and attach the policy from step 1.
  3. Edit the trust relationship for the IAM role to allow users from Account B to assume the role.
  4. Provide the users in Account B with the ability to assume the role, typically by adding permissions to their IAM user policy.

Resource-based Policies

Some AWS services, like S3, support resource-based policies that directly attach permissions policies to the resource itself. For example, an S3 bucket policy can grant read and write permissions to users from a different AWS account directly, without the need to use IAM roles.

Consider this example policy, which could be attached to an S3 bucket in Account A to allow Account B access:

{
“Version”: “2012-10-17”,
“Statement”: [
{
“Effect”: “Allow”,
“Principal”: {“AWS”: “arn:aws:iam::AccountB-ID:root”},
“Action”: [“s3:GetObject”, “s3:PutObject”],
“Resource”: “arn:aws:s3:::bucketname-in-accountA/*”
}
]
}

VPC Peering

AWS Virtual Private Cloud (VPC) allows you to isolate and control your cloud network space. When you need to enable direct network connectivity between VPCs in different AWS accounts, you can establish VPC peering. This allows resources in either VPC to communicate with each other using private IP addresses without routing the traffic through the public internet.

Keep in mind that VPC peering has some limitations:

  • Overlapping CIDR blocks are not allowed.
  • Transitive peering is not supported natively.
  • Limited to certain region pairings depending on service availability and policies.

AWS Resource Access Manager (RAM)

AWS RAM allows you to share AWS resources with any AWS account or through AWS Organizations. Unlike VPC peering, which is for networking resources, RAM can share many types of resources like Subnets, Transit Gateways, and License Configurations.

For example, you can share subnets with other AWS accounts using AWS RAM:

  1. The owner of the subnet (Account A) enables sharing with AWS RAM.
  2. Account A shares the specified subnet(s) with Account B by creating a resource share.
  3. Account B accepts the shared resource, and the subnet appears in their account.

AWS Organizations and Service Control Policies (SCPs)

AWS Organizations helps to manage and govern your environment as you scale with AWS. Using Service Control Policies (SCPs), you can define permissions for member accounts in your organization. SCPs can limit the services, actions, and resources that users and roles in each member account can use.

Consider the following organizing principles when adopting SCPs:

  • Policies are not directly attached to user roles or resources.
  • SCPs limit permissions in member accounts irrespective of the individual policies in those accounts.
  • SCPs are useful for broad strokes governance, like ensuring all member accounts adhere to certain security protocols.

Comparison Table

Resource Sharing Method Use Case Limitations
Cross-Account IAM Roles User or service access across accounts Trust relationships must be explicitly set
Resource-based Policies Resource access without roles or users Supported by few services
VPC Peering Network connectivity between VPCs Non-transitive, no CIDR overlap
AWS RAM Share multiple resource types Requires acceptance by the receiving account
SCPs in AWS Organizations Broad governance across multiple accounts Only limit permissions, do not grant them

Each of these sharing methods serves specific scenarios and should be selected based on the architecture requirements and compliance regulations applicable to your resources and workloads. By employing these sharing strategies thoughtfully, organizations can ensure efficient, secure, and compliant use of AWS resources across different AWS accounts.

Practice Test with Explanation

True or False: AWS Resource Access Manager (RAM) allows you to share your AWS Transit Gateways with other AWS accounts.

  • A) True
  • B) False

Answer: A) True

Explanation: AWS RAM enables you to easily and securely share AWS resources with any AWS account or through AWS Organizations.

Which AWS service enables cross-account access with fine-grained permission controls?

  • A) AWS IAM
  • B) AWS RAM
  • C) Amazon VPC
  • D) AWS Direct Connect

Answer: A) AWS IAM

Explanation: AWS Identity and Access Management (IAM) allows you to manage access to AWS services and resources securely, including setting permissions for cross-account resource access.

In a cross-account scenario, what feature can you use to allow an IAM user in Account B to access resources in Account A?

  • A) Resource-based policies
  • B) Access Control Lists (ACLs)
  • C) IAM roles
  • D) Security Groups

Answer: C) IAM roles

Explanation: IAM roles with trust policies can be used to grant an IAM user in one account permission to access resources in another account.

True or False: An S3 bucket policy cannot be used to grant read access to an S3 bucket to users from another AWS account.

  • A) True
  • B) False

Answer: B) False

Explanation: S3 bucket policies can be used to grant access permissions to users from other AWS accounts, making it possible to share S3 content across accounts.

When sharing an Amazon RDS snapshot with another AWS account, the snapshot can be:

  • A) Public
  • B) Private
  • C) Both A and B
  • D) Neither A nor B

Answer: C) Both A and B

Explanation: Amazon RDS snapshots can be shared as public or private with specific AWS accounts.

Which AWS service allows for cross-account billing?

  • A) AWS Organizations
  • B) AWS Budgets
  • C) AWS Cost Explorer
  • D) AWS RAM

Answer: A) AWS Organizations

Explanation: AWS Organizations supports consolidated billing that enables you to receive a single bill for multiple AWS accounts.

True or False: AWS Network Load Balancer cannot be shared across AWS accounts.

  • A) True
  • B) False

Answer: B) False

Explanation: AWS announced the capability for customers to share their Network Load Balancers across AWS accounts within the same region using AWS RAM.

True or False: AWS allows sharing Amazon EC2 instances directly across AWS accounts.

  • A) True
  • B) False

Answer: B) False

Explanation: While you cannot share EC2 instances directly across accounts, you can share custom Amazon Machine Images (AMIs) to launch EC2 instances in other accounts.

Which service or feature can be used to allow VPC resource sharing across AWS accounts?

  • A) AWS Resource Groups
  • B) VPC peering
  • C) AWS RAM
  • D) Amazon EC2 Auto Scaling

Answer: C) AWS RAM

Explanation: AWS RAM allows you to share Subnets, Transit Gateways, and other VPC resources across AWS accounts.

True or False: Cross-account sharing in AWS always implies resources are shared with full access permissions.

  • A) True
  • B) False

Answer: B) False

Explanation: Cross-account sharing allows the owner to define the level of access permissions, which doesn’t necessarily have to be full access; it can be read-only or custom permissions as well.

Interview Questions

What AWS service allows for the sharing of Amazon EC2 instances across different AWS accounts?

AWS Resource Access Manager (RAM) enables you to share your AWS resources with any AWS account or through AWS Organizations. While EC2 instances themselves cannot be shared, EC2 Reserved Instances or Capacity Reservations can be shared to optimize costs across accounts.

Can you explain how cross-account roles aid in managing multiple AWS accounts?

Cross-account roles allow one AWS account to delegate permissions to access resources to users, groups, or roles in another AWS account. They help in managing multiple accounts by providing a secure way to grant only the necessary permissions needed to perform specific tasks without sharing security credentials directly.

What is the benefit of using AWS Organizations for resource sharing?

AWS Organizations allows for the centralized management of multiple AWS accounts. It simplifies billing, access control, and compliance for those accounts, and allows for the sharing of resources such as Service Control Policies (SCPs) to enforce permission boundaries across accounts.

How can you share an Amazon S3 bucket with another AWS account?

To share an S3 bucket with another AWS account, you can use bucket policies or Access Control Lists (ACLs). Bucket policies provide more flexible permissions and are generally recommended for cross-account access.

What are the implications of sharing resources using cross-account VPC peering?

Cross-account VPC peering allows for direct network connectivity between two VPCs in different AWS accounts. It enables instances in either VPC to communicate with each other as if they are within the same network. However, users must be aware of the data transfer costs and the complexity of network routing rules that come with setting up cross-account VPC peering.

Is it possible to share AWS Direct Connect connections across multiple accounts?

Yes, you can share a Direct Connect connection across multiple accounts using AWS Direct Connect Gateway in conjunction with AWS RAM. This provides an efficient way to allow multiple VPCs, potentially in different accounts, to access the Direct Connect connection.

How do you implement cross-account access to an Amazon DynamoDB table?

Cross-account access to a DynamoDB table can be implemented by creating an IAM role with the necessary permissions and providing the role’s ARN to the other account. The other account assumes the role to interact with the DynamoDB table following the principle of least privilege.

What best practices would you recommend for secure cross-account resource sharing?

Best practices for secure cross-account resource sharing include: using AWS Organizations with Service Control Policies, implementing least privilege access using IAM roles, regularly auditing permissions, utilizing resource tags for better manageability, and using AWS CloudTrail for monitoring cross-account interactions.

How can you monitor cross-account activity to ensure security and compliance?

AWS CloudTrail can be used to monitor cross-account activity, ensuring that all API calls and resource accesses across accounts are logged and auditable. This is essential for maintaining security and compliance.

What steps should be taken if unauthorized cross-account resource access is detected?

Immediately revoke any potentially compromised permissions, investigate the extent of the unauthorized access using AWS CloudTrail logs, assess the impact on resources, and follow the incident response procedures. Implement necessary remediations and consider using AWS GuardDuty for future preventive monitoring.

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Guadalupe Roybal
5 months ago

Great insights on resource sharing across AWS accounts!

Julius Staab
7 months ago

This topic is super relevant for the AWS Certified Advanced Networking – Specialty exam.

Katie Jordan
6 months ago

Can anyone explain the security best practices for cross-account resource sharing?

Dale Dolfing
6 months ago

Appreciate the detailed blog post!

Venla Leino
6 months ago

Has anyone implemented cross-account VPC peering?

کیانا قاسمی

Good information, thanks!

Pepe Fernandes
6 months ago

I think the blog post could have covered cross-account roles in more detail.

Volkan Öztonga
6 months ago

Is there a performance impact when accessing shared resources across AWS accounts?

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