Cross-account resource sharing is a fundamental capability in AWS that enables organizations to securely share resources across multiple AWS accounts while maintaining proper governance and security controls. This approach is essential for enterprises implementing multi-account strategies to achiev…Cross-account resource sharing is a fundamental capability in AWS that enables organizations to securely share resources across multiple AWS accounts while maintaining proper governance and security controls. This approach is essential for enterprises implementing multi-account strategies to achieve workload isolation, billing separation, and security boundaries.
AWS provides several mechanisms for cross-account resource sharing:
**AWS Resource Access Manager (RAM):** This service allows you to share resources like VPC subnets, Transit Gateways, Route 53 Resolver rules, and License Manager configurations with other accounts within your organization or with specific AWS accounts. RAM simplifies resource sharing while reducing operational overhead.
**Resource-based Policies:** Many AWS services support resource-based policies that grant cross-account access. Services like S3, KMS, SNS, SQS, and Lambda allow you to attach policies specifying which external accounts or principals can access the resource and what actions they can perform.
**IAM Roles for Cross-account Access:** Organizations can create IAM roles that trusted accounts can assume. This enables secure, temporary credential-based access to resources in another account through the AssumeRole API call.
**AWS Organizations Integration:** When accounts belong to the same AWS Organization, sharing becomes more streamlined. Service Control Policies (SCPs) can govern what resources can be shared and accessed across organizational units.
**VPC Peering and Transit Gateway:** For network-level resource sharing, VPC peering connections or Transit Gateway attachments enable private network connectivity between accounts, allowing resources to communicate securely.
**Key Considerations:**
- Implement least privilege principles when granting cross-account access
- Use AWS Organizations for centralized management
- Monitor cross-account access using CloudTrail
- Establish clear naming conventions and tagging strategies
- Document resource sharing relationships for compliance and auditing
Cross-account resource sharing reduces duplication, optimizes costs, and enables collaborative architectures while preserving security boundaries between different teams, environments, or business units.
Cross-Account Resource Sharing in AWS
Why Cross-Account Resource Sharing is Important
In enterprise environments, organizations typically operate multiple AWS accounts for various reasons: security isolation, billing separation, development and production environments, or different business units. Cross-account resource sharing enables these accounts to collaborate efficiently while maintaining security boundaries. This capability is essential for implementing least-privilege access, centralizing shared services, and reducing resource duplication across accounts.
What is Cross-Account Resource Sharing?
Cross-account resource sharing refers to the mechanisms and services AWS provides to allow resources in one AWS account to be accessed or used by principals (users, roles, services) in another AWS account. This enables organizations to share infrastructure, data, and services across account boundaries while maintaining proper governance and security controls.
Key AWS Services and Methods for Cross-Account Sharing
1. AWS Resource Access Manager (RAM) RAM allows you to share AWS resources with other accounts or within your AWS Organization. Shareable resources include: - VPC Subnets - Transit Gateways - Route 53 Resolver Rules - License Manager configurations - AWS Outposts - Aurora DB Clusters
2. IAM Role-Based Cross-Account Access You can create IAM roles in one account that can be assumed by principals in another account. This involves: - Creating a role with a trust policy allowing the external account - The external account's users or roles use sts:AssumeRole to obtain temporary credentials
3. Resource-Based Policies Many AWS services support resource-based policies that can grant access to external accounts: - S3 bucket policies - KMS key policies - SNS topic policies - SQS queue policies - Lambda function policies - Secrets Manager secret policies
4. AWS Organizations Service Control Policies (SCPs) SCPs define permission guardrails across accounts within an organization, controlling what actions member accounts can perform.
5. VPC Peering and Transit Gateway Enable network connectivity between VPCs in different accounts for resource communication.
How Cross-Account Resource Sharing Works
Trust Relationships: The resource-owning account must explicitly trust the accessing account through policies or configurations.
Principal Specification: Policies specify which external principals (accounts, roles, or users) can access resources using ARNs.
Permission Evaluation: Access requires both the resource policy to allow access AND the principal's identity policy to permit the action. Both sides must grant permission.
External ID: For enhanced security when third parties assume roles, an external ID can be required in the trust policy to prevent confused deputy attacks.
Common Cross-Account Patterns
- Centralized Logging: All accounts send logs to a central logging account's S3 bucket or CloudWatch Logs - Shared Services VPC: Common services hosted in one account, accessed via VPC sharing or peering - Central Security Account: Security tools and audit roles accessing resources across all accounts - CI/CD Pipelines: Deployment pipelines in one account deploying to multiple environment accounts
Exam Tips: Answering Questions on Cross-Account Resource Sharing
1. Identify the Sharing Method: Determine whether the scenario requires RAM, IAM roles, or resource-based policies. RAM is preferred for VPC subnets and Transit Gateways within Organizations.
2. Remember the Two-Policy Requirement: For IAM role-based access, the trust policy in the target account AND the permissions in the source account must both allow the action.
3. Know Service-Specific Behaviors: Some services like S3 can grant cross-account access through bucket policies alone, while others require role assumption.
4. Organizations vs. Non-Organizations: RAM sharing is simpler within an AWS Organization. Outside Organizations, sharing requires accepting invitations.
5. Consider KMS Implications: When sharing encrypted resources, the KMS key policy must also grant cross-account access, and the key must be a customer-managed key (CMK), not AWS-managed.
6. Look for Security Keywords: Questions mentioning 'least privilege' or 'temporary credentials' often point toward IAM role assumption rather than sharing long-term credentials.
7. External ID Usage: When third-party vendors need access to your account, external IDs in trust policies provide additional security.
8. Evaluate Answer Choices: Eliminate options that require sharing long-term credentials or root account access. Prefer solutions using temporary credentials and role assumption.
9. Network Considerations: For resources requiring network connectivity across accounts, consider whether VPC peering, Transit Gateway, or PrivateLink is most appropriate based on scale and complexity.