Tutorial / Cram Notes

One of the primary methods for managing cross-account access in AWS is through the use of IAM roles. IAM roles allow you to delegate access with defined permissions to users, applications, or services without having to share long-term access keys. You can assume a role within your own account or in another account. Here’s how you can evaluate cross-account roles:

  • Evaluate Permissions: When creating an IAM role for cross-account access, it’s important to evaluate the permissions the role grants. The permissions should follow the principle of least privilege, granting only the necessary rights to perform a given task.
  • Trust Relationships: These roles must include trust policies that specify which accounts are allowed to assume them. You’ll need to evaluate the trust relationship to ensure it includes the correct trusted account.
  • Security: Evaluating how keys are managed is crucial. When assuming a role, AWS provides temporary security credentials that are automatically rotated.

Example of Creating a Cross-Account Role

To create a role in Account A that can be assumed by Account B, you would take the following high-level steps:

  1. In Account A, create an IAM role with the desired permissions.
  2. Define a trust relationship in the role to allow Account B to assume the role.

{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::ACCOUNT-B-ID:root"
},
"Action": "sts:AssumeRole",
"Condition": {}
}
]
}

  1. In Account B, grant your users permission to assume the role from Account A.

{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": "sts:AssumeRole",
"Resource": "arn:aws:iam::ACCOUNT-A-ID:role/RoleName"
}
]
}

AWS Organizations for Centralized Management

With AWS Organizations, you can create and manage multiple AWS accounts. It offers policies called Service Control Policies (SCPs) that provide central control over the maximum available permissions for all accounts in your organization.

  • Service Control Policies (SCPs): SCPs enable you to whitelist or blacklist permissions for all IAM entities in your member accounts. When evaluating SCPs, you must ensure that these policies do not conflict with the necessary permissions for cross-account operations.
  • Consolidated Billing: AWS Organizations allows for consolidated billing, which simplifies the cost management across multiple accounts. Evaluating your account setup for optimal budgeting and cost allocation is also part of cross-account access management.
  • Organizational Units (OUs): You can use OUs to group accounts and apply SCPs to each OU, managing permissions on a larger scale.

Resource-Based Policies

Resource-based policies are attached directly to AWS resources and specify who has permission to access the resource and what actions they can perform.

  • Usage in Cross-Account Access: When evaluating the use of resource-based policies, consider that these policies can grant access to users, roles, or AWS accounts outside of their own account.
  • Security Concerns: Since resource-based policies can grant access broadly, it is crucial to review them regularly to avoid unintended permissions that might be exploitable.

Best Practices

When evaluating cross-account access management, here are some best practices to consider:

  • Regular Audits: Regularly audit your cross-account permissions using tools like AWS IAM Access Analyzer to ensure that policies are up-to-date and align with the company’s security guidelines.
  • Automated Policy Management: Utilize automation for policy updates, ensuring consistency across accounts.
  • Secure Sharing: When using cross-account roles, prefer using IAM roles over key-sharing and ensure that the AssumeRole permission is tightly scoped.

By taking these measures and practices into account, you can build a secure, compliant, and effective cross-account access management strategy, which is a critical area of expertise for the AWS Certified Solutions Architect – Professional.

Practice Test with Explanation

True/False: Cross-account access in AWS allows you to access resources in another AWS account as if they were in your own account.

  • True

Correct answer: True

Explanation: Cross-account access in AWS is a method that lets you access resources across different AWS accounts in a secure manner, providing permissions to perform actions as though the resources were within your own account.

Which AWS service is primarily used to manage cross-account access?

  • A) AWS IAM (Identity and Access Management)
  • B) AWS S3 (Simple Storage Service)
  • C) AWS EC2 (Elastic Compute Cloud)
  • D) AWS CloudTrail

Correct answer: A) AWS IAM (Identity and Access Management)

Explanation: AWS IAM is the service used to manage access and permissions across AWS services, which includes the ability to configure cross-account access through roles and policies.

In a cross-account role, who is the trusted entity?

  • A) The resource server
  • B) The AWS account that owns the role
  • C) The external AWS account that is given access
  • D) Both B and C are correct

Correct answer: D) Both B and C are correct

Explanation: In a cross-account role, the trusted entity can be both the account that owns the role (trusting account) and the external accounts or users (trusted accounts) that are granted permissions.

True/False: To enable a user from Account A to access resources in Account B, Account B must create a resource-based policy rather than using IAM roles.

  • False

Correct answer: False

Explanation: Account B can use IAM roles with a trust policy to grant access to users in Account A, rather than having to create a resource-based policy.

Which policy type enables cross-account access when applied to an IAM role?

  • A) Identity-based policy
  • B) Resource-based policy
  • C) SCP (Service Control Policies)
  • D) Trust policy

Correct answer: D) Trust policy

Explanation: A trust policy is applied to an IAM role to establish a trust relationship between two AWS accounts, enabling cross-account access.

True/False: Cross-account access can be achieved without sharing IAM user credentials between accounts.

  • True

Correct answer: True

Explanation: Cross-account access is typically achieved through roles and policies, which do not require the sharing of IAM user credentials between accounts.

After setting up a cross-account role for Account A to access resources in Account B, what must a user in Account A do to start using the resources?

  • A) Log in to Account B with an IAM user
  • B) Assume the cross-account role from Account A
  • C) Share the resource’s ARN with Account A
  • D) Create an identical IAM role in Account A

Correct answer: B) Assume the cross-account role from Account A

Explanation: A user in Account A must assume the cross-account role granted by Account B to access the resources without the need to log in directly to Account B.

The use of AWS Organizations facilitates automatic cross-account access between accounts within the same organization.

  • A) True
  • B) False

Correct answer: B) False

Explanation: AWS Organizations does not automatically enable cross-account access between accounts. It is used for account management and governance. Cross-account access must still be explicitly set up via IAM roles and trust policies.

True/False: An IAM user can assume multiple roles at the same time to access resources in different accounts.

  • False

Correct answer: False

Explanation: An IAM user can assume only one role at a time. To access resources in different accounts simultaneously, they would need to assume each role in separate sessions.

The external ID is an optional feature in IAM roles trust policy to ensure security when granting cross-account access.

  • A) True
  • B) False

Correct answer: A) True

Explanation: The external ID is an optional feature that is used as a shared secret between the trusting and trusted account, enhancing the security of the cross-account role when third-party services are involved.

True/False: It is recommended to use the same IAM role across multiple AWS accounts for simplicity when setting up cross-account access.

  • False

Correct answer: False

Explanation: It is recommended to use separate IAM roles tailored to each AWS account’s access requirements to ensure the principle of least privilege.

An organization can use AWS Resource Access Manager (RAM) to share resources with external accounts.

  • A) True
  • B) False

Correct answer: A) True

Explanation: AWS RAM is a service that allows you to share AWS resources with any AWS account or within your organization, helping to manage cross-account resource access.

Interview Questions

What is the purpose of cross-account access in AWS, and when might it be necessary?

The purpose of cross-account access is to allow users or services in one AWS account to access resources in another AWS account. This is often necessary when organizations are managing multiple AWS accounts and need to share resources such as S3 buckets, or when they are collaborating with external partnerships that require access to certain resources without having to replicate them.

Can you describe what a resource-based policy is and how it differs from an identity-based policy in the context of AWS cross-account access?

A resource-based policy is attached directly to an AWS resource and specifies who (principally which accounts, users, or roles) has permissions to access that resource. In contrast, an identity-based policy is attached to IAM users, groups, or roles within an AWS account and specifies what resources they can access. In cross-account scenarios, resource-based policies allow the owner of the accessed resource to maintain control over who can access it, regardless of the account.

What are AWS Organizations and how do they relate to cross-account access management?

AWS Organizations is a service that allows you to manage and govern your environment across multiple AWS accounts. With an organization, you can centrally manage policies, security, and automation settings, and streamline billing. It supports cross-account access management by enabling service control policies (SCPs) that apply permissions across all accounts within the organization.

How can you use IAM roles to delegate cross-account access, and what are the benefits?

IAM roles for cross-account access can be created with a trust policy that allows principals from another AWS account to assume the role. The benefit of using IAM roles is that they do not require sharing of security credentials between accounts and provide a secure way to delegate permissions to users from another account.

What is External ID, and why is it important when setting up a cross-account access role?

External ID is an optional field that you can use when setting up an IAM role for cross-account access. It acts as a secret key to prevent the “confused deputy” problem, where an unauthorized third party could coerce a trusted entity to act on their behalf. When configuring a role for another account to assume, using an External ID that the trusting account generates ensures the trust is not inadvertently extended to others.

Explain how AWS STS (Security Token Service) is utilized within cross-account role assumption.

AWS STS is a web service that lets you request temporary, limited-privilege credentials for IAM users or for users that you authenticate. When assuming a cross-account role, STS provides a set of temporary security credentials that the assuming account’s user can use to make AWS API calls. This is more secure than sharing long-term access keys because the credentials are temporary and automatically expire.

How does the ‘Principal’ element in an IAM policy work in cross-account scenarios?

In a cross-account scenario, the ‘Principal’ element in an IAM policy or resource-based policy is used to specify the external AWS account, IAM user, or IAM role that is allowed to access the resource. It indicates who is trusted to access the resource when the policy is evaluated during an access attempt.

Describe the concept of least privilege and how it should be applied in cross-account access management.

The principle of least privilege means giving an IAM user or role the minimum level of access necessary to perform its tasks. In cross-account access management, this means ensuring that the policies applied to cross-account roles strictly limit the permissions to what is necessary for the tasks at hand and exclude any unnecessary permissions that could be exploited for malicious purposes.

How can Amazon CloudTrail be used to monitor cross-account activity?

Amazon CloudTrail can be used to log, continuously monitor, and retain account activity related to actions across all AWS infrastructure. With CloudTrail, you can detect unusual activity in your AWS accounts, including cross-account actions, by collecting information on API calls made or changes to IAM policies and roles. These logs can be analyzed to ensure compliance and audit cross-account interactions.

What is AWS Resource Access Manager (RAM), and how does it facilitate resource sharing across accounts?

AWS Resource Access Manager (RAM) is a service that enables you to share AWS resources with any AWS account or within your AWS Organization. It simplifies the process of sharing resources like Subnets, Transient Gateway, and License configurations, without having to create duplicate resources in multiple accounts. RAM ensures that resource sharing is both secure and efficient, helping manage cross-account access centrally.

Can you explain what a service control policy (SCP) is and how it is used in conjunction with cross-account access within AWS Organizations?

A service control policy (SCP) is a type of policy that can be applied to all AWS accounts within an AWS Organization, or to specific organizational units (OUs) within an organization. SCPs specify the maximum permissions for an account, essentially creating guardrails—regardless of the individual identity-based or resource-based policies. This helps to ensure that even with cross-account access, actions performed across accounts do not exceed the organization’s defined compliance and security boundaries.

Explain the difference between sharing resources using cross-account roles and using resource sharing features such as those provided by AWS RAM.

Sharing resources using cross-account roles involves creating IAM roles with policies granting the necessary permissions, which users or services in other accounts can assume to access resources. On the other hand, resource sharing features like AWS RAM allow sharing of specific AWS resources directly with other accounts without creating IAM roles. While IAM roles offer fine-grained access control and are commonly used for user access, AWS RAM is optimized for straightforward resource sharing at the resource level, especially useful for supported services like VPC Subnets, Route 53 Resolver rules, etc.

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Christian Nieto
6 months ago

Great blog post! It helped me understand the nuances of cross-account access management in AWS.

Silvia Peña
6 months ago

Can someone explain the difference between resource-based policies and identity-based policies in AWS?

Morgane Fontai
6 months ago

How effective is AWS IAM in managing cross-account access compared to other cloud providers?

سینا پارسا

This post is extremely helpful for understanding cross-account access management for the AWS Certified Solutions Architect – Professional exam.

Lucia Cruz
6 months ago

Can anyone explain more about resource-based policies vs. role assumptions?

Austin Woods
6 months ago

Appreciate the detailed steps! This is a great tutorial!

Isabelle Kumar
6 months ago

Why do we need both resource-based policies and roles for cross-account access?

Velibor Živanović

Thanks for this comprehensive guide. It sums up what I needed!

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