Identity-based policies are attached to an identity, such as IAM users, groups of users, and roles. These are IAM policy documents that control what actions an identity can perform, on which resources, and under what conditions. Identity-based policies can be managed or inline policies.
Resource-based policies are IAM policy documents that you attach to a resource, such as a DynamoDB table. These policies grant the specified principal permission to perform specific actions on that resource and defines under what conditions this applies. For example, the resource-based policy for a DynamoDB table also includes the index associated with the table. Resource-based policies are inline policies. There are no managed resource-based policies.
For more information about these policies, see Identity-based policies and resource-based policies in the IAM User Guide.
If the IAM principal is from the same account as the resource owner, a resource-based policy is sufficient to specify access permissions to the resource. You can still choose to have an IAM identity-based policy along with a resource-based policy. For cross-account access, you must explicitly allow access in both the identity and resource policies as specified in Cross-account access with resource-based policies in DynamoDB. When you use both types of policies, a policy is evaluated as described in Determining whether a request is allowed or denied within an account.
