When do I use IAM?
When you are performing different job functions
Amazon Identity and Access Management is a core infrastructure service that provides the foundation for access control based on identities within Amazon. You use IAM every time you access your Amazon account.
How you use IAM differs, depending on the work that you do in Amazon.
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Service user – If you use an Amazon service to do your job, then your administrator provides you with the credentials and permissions that you need. As you use more advanced features to do your work, you might need additional permissions. Understanding how access is managed can help you request the right permissions from your administrator.
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Service administrator – If you're in charge of an Amazon resource at your company, you probably have full access to IAM. It's your job to determine which IAM features and resources your service users should access. You must then submit requests to your IAM administrator to change the permissions of your service users. Review the information on this page to understand the basic concepts of IAM.
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IAM administrator – If you're an IAM administrator, you manage IAM identities and write policies to manage access to IAM.
When you are authorized to access Amazon resources
Authentication is how you sign in to Amazon using your identity credentials. You must be authenticated (signed in to Amazon) as the Amazon Web Services account root user, as an IAM user, or by assuming an IAM role.
If you access Amazon programmatically, Amazon provides a software development kit (SDK) and a command line interface (CLI) to cryptographically sign your requests by using your credentials. If you don't use Amazon tools, you must sign requests yourself. For more information about using the recommended method to sign requests yourself, see Signing Amazon API requests in the IAM User Guide.
Regardless of the authentication method that you use, you might be required to provide additional security information. For example, Amazon recommends that you use multi-factor authentication (MFA) to increase the security of your account. To learn more, see Using multi-factor authentication (MFA) in Amazon in the IAM User Guide.
When you sign-in as an IAM user
An IAM user is an identity within your Amazon Web Services account that has specific permissions for a single person or application. Where possible, we recommend relying on temporary credentials instead of creating IAM users who have long-term credentials such as passwords and access keys. However, if you have specific use cases that require long-term credentials with IAM users, we recommend that you rotate access keys. For more information, see Rotate access keys regularly for use cases that require long-term credentials in the IAM User Guide.
An IAM group is an identity that specifies a collection of IAM users. You can't sign in as a group. You can use groups to specify permissions for multiple users at a time. Groups make permissions easier to manage for large sets of users. For example, you could have a group named IAMAdmins and give that group permissions to administer IAM resources.
Users are different from roles. A user is uniquely associated with one person or application, but a role is intended to be assumable by anyone who needs it. Users have permanent long-term credentials, but roles provide temporary credentials. To learn more, see When to create an IAM user (instead of a role) in the IAM User Guide.
When you assume an IAM role
An IAM role is an identity within your Amazon Web Services account that has specific permissions. It is similar to an IAM user, but is not associated with a specific person. You can temporarily assume an IAM role in the Amazon Web Services Management Console by switching roles. You can assume a role by calling an Amazon CLI or Amazon API operation or by using a custom URL. For more information about methods for using roles, see Using IAM roles in the IAM User Guide.
IAM roles with temporary credentials are useful in the following situations:
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Federated user access – To assign permissions to a federated identity, you create a role and define permissions for the role. When a federated identity authenticates, the identity is associated with the role and is granted the permissions that are defined by the role. For information about roles for federation, see Creating a role for a third-party Identity Provider in the IAM User Guide.
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Temporary IAM user permissions – An IAM user or role can assume an IAM role to temporarily take on different permissions for a specific task.
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Cross-account access – You can use an IAM role to allow someone (a trusted principal) in a different account to access resources in your account. Roles are the primary way to grant cross-account access. However, with some Amazon Web Services, you can attach a policy directly to a resource (instead of using a role as a proxy). To learn the difference between roles and resource-based policies for cross-account access, see How IAM roles differ from resource-based policies in the IAM User Guide.
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Cross-service access – Some Amazon Web Services use features in other Amazon Web Services. For example, when you make a call in a service, it's common for that service to run applications in Amazon EC2 or store objects in Amazon S3. A service might do this using the calling principal's permissions, using a service role, or using a service-linked role.
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Forward access sessions (FAS) – When you use an IAM user or role to perform actions in Amazon, you are considered a principal. When you use some services, you might perform an action that then initiates another action in a different service. FAS uses the permissions of the principal calling an Amazon Web Service, combined with the requesting Amazon Web Service to make requests to downstream services. FAS requests are only made when a service receives a request that requires interactions with other Amazon Web Services or resources to complete. In this case, you must have permissions to perform both actions. For policy details when making FAS requests, see Forward access sessions.
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Service role – A service role is an IAM role that a service assumes to perform actions on your behalf. An IAM administrator can create, modify, and delete a service role from within IAM. For more information, see Creating a role to delegate permissions to an Amazon Web Service in the IAM User Guide.
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Service-linked role – A service-linked role is a type of service role that is linked to an Amazon Web Service. The service can assume the role to perform an action on your behalf. Service-linked roles appear in your Amazon Web Services account and are owned by the service. An IAM administrator can view, but not edit the permissions for service-linked roles.
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Applications running on Amazon EC2 – You can use an IAM role to manage temporary credentials for applications that are running on an EC2 instance and making Amazon CLI or Amazon API requests. This is preferable to storing access keys within the EC2 instance. To assign an Amazon role to an EC2 instance and make it available to all of its applications, you create an instance profile that is attached to the instance. An instance profile contains the role and enables programs that are running on the EC2 instance to get temporary credentials. For more information, see Using an IAM role to grant permissions to applications running on Amazon EC2 instances in the IAM User Guide.
To learn whether to use IAM roles or IAM users, see When to create an IAM role (instead of a user) in the IAM User Guide.
When you create policies and permissions
You grant permissions to a user by creating a policy, which is a document that lists the actions that a user can perform and the resources those actions can affect. Any actions or resources that are not explicitly allowed are denied by default. Policies can be created and attached to principals (users, groups of users, roles assumed by users, and resources).
These policies are used with an IAM role:
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Trust policy – Defines which principals can assume the role, and under which conditions. A trust policy is a specific type of resource-based policy for IAM roles. A role can have only one trust policy.
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Identity-based policies (inline and managed) – These policies define the permissions that the user of the role is able to perform (or is denied from performing), and on which resources.
Use the Example IAM identity-based policies to help you define permissions for your IAM identities. After you find the policy that you need, choose view the policy to view the JSON for the policy. You can use the JSON policy document as a template for your own policies.
Note
If you are using IAM Identity Center to manage your users, you assign permission sets in IAM Identity Center instead of attaching a permissions policy to a principal. When you assign a permission set to a group or user in Amazon IAM Identity Center, IAM Identity Center creates corresponding IAM roles in each account, and attaches the policies specified in the permission set to those roles. IAM Identity Center manages the role, and allows the authorized users you’ve defined to assume the role. If you modify the permission set, IAM Identity Center ensures that the corresponding IAM policies and roles are updated accordingly.
For more information about IAM Identity Center, see What is IAM Identity Center? in the Amazon IAM Identity Center User Guide.