Service-linked roles are a unique category of IAM (Identity and Access Management) roles in AWS, and they play a crucial role in enabling AWS services to perform actions on your behalf securely. Here’s a comprehensive explanation of the key aspects related to service-linked roles and how they operate:
1. Service-Linked Roles Defined:
A service-linked role is a specific type of IAM role directly associated with an AWS service. These roles are preconfigured and maintained by the service itself. They come with all the necessary permissions required for that service to make calls to other AWS services on your behalf. In essence, service-linked roles serve as intermediaries that facilitate the interaction between AWS services and other AWS resources.
2. Creation and Management:
The linked AWS service defines how service-linked roles are created, modified, and deleted. The creation and deletion processes can vary depending on the service’s requirements. Some services may automatically create or delete service-linked roles when certain actions or resources are used, while others may provide options within their service console, API, or CLI for you to manage these roles. Regardless of the method, the primary goal of service-linked roles is to simplify the setup process for a service by eliminating the need for manually configuring permissions.
3. Service-Linked Roles vs. Service Roles:
It’s essential to distinguish between service-linked roles and service roles. Service roles are also IAM roles, but they are roles assumed by services to perform actions on your behalf. The significant difference is that service roles can be created, modified, and deleted by IAM administrators, giving you more control over their permissions. On the other hand, service-linked roles are owned and managed by the service, and you can only view their permissions, not modify them.
4. Permissions and Trust Policies:
The permissions for service-linked roles, including the trust policy and permissions policy, are defined by the linked service. These permissions are tailored to meet the specific requirements of that service, ensuring that it can execute tasks without unnecessary limitations or risks. Importantly, the permissions policy for a service-linked role cannot be attached to any other IAM entity, providing isolation and security.
5. Deleting Service-Linked Roles:
Before you can delete a service-linked role, you must first delete any related resources that depend on it. This safeguard ensures that you don’t inadvertently revoke access to essential resources. Deleting the role is a step-by-step process that necessitates the removal of associated resources and verifying that the role is no longer actively in use.
6. Permissions Configuration:
To configure permissions for an IAM entity (either a user or a role) to create or edit a service-linked role, you must attach specific policies to the entity. These policies define the necessary actions and resources, allowing them to manage service-linked roles. You can configure permissions to allow users to create specific service-linked roles, any service-linked role, edit role descriptions, delete specific service-linked roles, or delete any service-linked role.
7. Indirect Permissions:
Service-linked roles can indirectly transfer their permissions to other users and roles. When a service-linked role is used by an AWS service, it can utilize its permissions to make calls to other AWS services. This means that users and roles with permissions to call a service that employs a service-linked role may gain indirect access to those other services as well.
8. Clean Up Before Deletion:
As mentioned earlier, before deleting a service-linked role, you must ensure that the role has no active sessions and remove any resources associated with it. Cleaning up resources is essential to avoid inadvertently causing disruptions to services that rely on the role.
9. Creation and Deletion Methods:
The method used to create or delete a service-linked role depends on the linked service. Some services create the roles automatically, while others provide options to create or delete them using their console, API, or CLI. If a service does not support manual creation or deletion, you can use the IAM service to create service-linked roles.
10. Limitations and Exceeding IAM Role Limits:
Service-linked roles count toward the limit of IAM roles in an AWS account. However, they have the unique ability to exceed this limit. This means that even if you’ve reached your maximum limit for roles, you can still create and use service-linked roles in your account.
In summary, service-linked roles play a vital role in simplifying the management of permissions between AWS services and other AWS resources. They are specifically designed and configured by the linked service to ensure the seamless execution of tasks. Understanding their creation, permissions, and deletion processes is essential for maintaining secure and efficient operations within your AWS environment.