Assuming IAM roles is a fundamental security concept in AWS that allows users, applications, or AWS services to temporarily obtain a set of credentials with specific permissions. Instead of sharing long-term access keys, role assumption provides a more secure approach to granting access to AWS reso…Assuming IAM roles is a fundamental security concept in AWS that allows users, applications, or AWS services to temporarily obtain a set of credentials with specific permissions. Instead of sharing long-term access keys, role assumption provides a more secure approach to granting access to AWS resources.
When you assume a role, you exchange your current credentials for temporary security credentials associated with that role. These temporary credentials include an access key ID, secret access key, and a security token, typically valid for 15 minutes to 12 hours.
The process works through AWS Security Token Service (STS). When an entity wants to assume a role, it calls the sts:AssumeRole API. AWS STS verifies that the requesting entity is allowed to assume the role by checking the role's trust policy. If permitted, STS returns temporary credentials.
Key components include:
1. Trust Policy: Defines who can assume the role. This JSON document specifies trusted principals (AWS accounts, services, or users) that are permitted to assume the role.
2. Permission Policy: Defines what actions the role can perform once assumed. This determines the actual permissions granted.
Common use cases include:
- Cross-account access: Users in one AWS account assuming roles in another account
- EC2 instance profiles: Applications running on EC2 accessing AWS services
- Lambda execution roles: Functions accessing other AWS resources
- Federation: External users obtaining temporary AWS access
For developers, the AWS SDKs handle credential management when assuming roles. You can configure role assumption in your application code or through credential profiles.
Best practices include following the principle of least privilege when defining role permissions, using conditions in trust policies to restrict when roles can be assumed, and implementing proper session duration limits based on your security requirements. Role assumption provides a secure, auditable way to manage access across AWS environments.
Assuming IAM Roles - AWS Developer Associate
Why Assuming IAM Roles is Important
Assuming IAM roles is a fundamental security concept in AWS that enables secure, temporary access to AWS resources. It eliminates the need for sharing long-term credentials, follows the principle of least privilege, and provides a secure way for users, applications, and AWS services to access resources across accounts or within the same account.
What is Assuming an IAM Role?
An IAM role is an AWS identity with specific permissions that can be assumed by trusted entities. Unlike IAM users, roles do not have permanent credentials. Instead, when an entity assumes a role, AWS Security Token Service (STS) provides temporary security credentials consisting of:
These credentials expire after a configurable period (15 minutes to 12 hours by default).
How Assuming Roles Works
Step 1: Role Creation An administrator creates a role with a trust policy that defines who can assume the role and a permissions policy that defines what actions the role can perform.
Step 2: AssumeRole API Call The trusted entity calls the sts:AssumeRole API, providing the role ARN and optionally an external ID or session name.
Step 3: STS Validation AWS STS validates that the requester is allowed to assume the role based on the trust policy.
Step 4: Temporary Credentials Returned If validated, STS returns temporary credentials that the entity uses to make AWS API calls.
Key Components of Role Assumption
Trust Policy: A JSON document attached to the role specifying which principals can assume the role.
Permissions Policy: Defines what AWS resources and actions the role grants access to.
External ID: An optional identifier used for cross-account access to prevent the confused deputy problem.
Session Duration: The length of time temporary credentials remain valid.
Common Use Cases
• Cross-Account Access: Users in Account A assuming a role in Account B • EC2 Instance Roles: Applications on EC2 instances accessing AWS services • Lambda Execution Roles: Lambda functions accessing other AWS resources • Federation: External users assuming roles via SAML or web identity federation • Service Roles: AWS services performing actions on your behalf
Important STS API Actions
• AssumeRole: For IAM users or roles assuming another role • AssumeRoleWithSAML: For SAML-based federation • AssumeRoleWithWebIdentity: For web identity providers like Amazon Cognito, Google, or Facebook • GetSessionToken: For MFA-protected API access
Exam Tips: Answering Questions on Assuming IAM Roles
1. Understand Trust Policies: When a question describes access denied errors when assuming a role, check if the trust policy allows the principal to assume the role.
2. Know the Credential Chain: Temporary credentials from assumed roles take precedence over instance profile credentials when explicitly used.
3. Cross-Account Scenarios: For cross-account access questions, remember that both accounts need proper configuration - the trusting account needs the role with trust policy, and the trusted account needs permission to call sts:AssumeRole.
4. External ID Usage: When questions mention third-party access or confused deputy scenarios, external ID is the solution.
5. Session Duration Limits: Default is 1 hour, maximum is 12 hours for most roles. Role chaining limits session to 1 hour.
6. Service-Linked Roles: These are predefined by AWS services and cannot be modified - only AWS can assume them.
7. Revocation: To revoke active sessions, use the Revoke Session feature which adds a condition to deny all actions for tokens issued before a specific time.
8. Watch for Permission Boundaries: Even if a role has permissions, permission boundaries can restrict the effective permissions.
Common Exam Scenarios
• Lambda function needs to access DynamoDB → Lambda execution role with DynamoDB permissions • User needs temporary elevated privileges → Assume a role with higher permissions • Application on EC2 needs S3 access → Use instance profile with IAM role • Third-party needs access to your resources → Cross-account role with external ID