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IAM Access Policies

Manage access in AWS by creating policies and attaching them to IAM identities (users, groups of users, or roles) or AWS resources. A policy is an object in AWS that, when associated with an identity or resource, defines their permissions. AWS evaluates these policies when an IAM principal (user or role) makes a request. Permissions in the policies determine whether the request is allowed or denied. Most policies are stored in AWS as JSON documents.

Policy types​

The following policy types, listed in order from most frequently used to less frequently used, are available for use in AWS.

  1. Identity-based policies – Attach managed and inline policies to IAM identities (users, groups to which users belong, or roles). Identity-based policies grant permissions to an identity.

  2. Resource-based policies – Attach inline policies to resources. The most common examples of resource-based policies are Amazon S3 bucket policies and IAM role trust policies. Resource-based policies grant permissions to the principal that is specified in the policy. Principals can be in the same account as the resource or in other accounts.

  3. Permissions boundaries – Use a managed policy as the permissions boundary for an IAM entity (user or role). That policy defines the maximum permissions that the identity-based policies can grant to an entity, but does not grant permissions. Permissions boundaries do not define the maximum permissions that a resource-based policy can grant to an entity.

  4. AWS Organizations SCPs – Use an AWS Organizations service control policy (SCP) to define the maximum permissions for IAM users and IAM roles within accounts in your organization or organizational unit (OU). SCPs limit permissions that identity-based policies or resource-based policies grant to IAM users or IAM roles within the account. SCPs do not grant permissions.

  5. AWS Organizations RCPs – Use an AWS Organizations resource control policy (RCP) to define the maximum permissions for resources within accounts in your organization or organizational unit (OU). RCPs limit permissions that identity-based and resource-based policies can grant to resources in accounts within your organization. RCPs do not grant permissions.

  6. Access control lists (ACLs) – Use ACLs to control which principals in other accounts can access the resource to which the ACL is attached. ACLs are similar to resource-based policies, although they are the only policy type that does not use the JSON policy document structure. ACLs are cross-account permissions policies that grant permissions to the specified principal. ACLs cannot grant permissions to entities within the same account.

  7. Session policies – Pass advanced session policies when you use the AWS CLI or AWS API to assume a role or a federated user. Session policies limit the permissions that the role or user's identity-based policies grant to the session. Session policies limit permissions for a created session, but do not grant permissions. For more information, see Session Policies.

Policies and permissions in AWS Identity and Access Management - AWS Identity and Access Management

Trust policy​

Trust policies define which principal entities (accounts, users, roles, and federated users) can assume the role. An IAM role is both an identity and a resource that supports resource-based policies. For this reason, you must attach both a trust policy and an identity-based policy to an IAM role. The IAM service supports only one type of resource-based policy called a role trust policy, which is attached to an IAM role.