Terraform guide to IAM Policies: The Two Cases You Need to Know

When working with IAM policies in Terraform, it's essential to know when to use a pre-existing managed policy and when to create a custom policy. If AWS provides a managed policy that meets your needs, use a policy attachment resource. If not, create a custom policy document using the aws_iam_policy_document data source. This distinction helps avoid confusion and ensures accurate IAM setup. To follow best practices, use managed policies when possible and create custom policies only when necessary. This approach simplifies IAM management and reduces errors.