What are service-linked roles?

IAM Service-linked roles are used to enable trusted services to perform tasks on behalf of the organization's member accounts, providing an easier and more secure way to delegate permissions to AWS services. When a service-linked role links to an AWS service, that is called a linked service. Only linked services can assume a service-linked role. All actions performed on your behalf by an AWS service using a service-linked role appears in AWS CloudTrail Logs.

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Blog for Service-Linked Roles