AWS allows users to assign metadata to their resources through tags, and these tags enable better classification and tracking of resources. Each tag is defined by a key and an operational value which is customer defined and makes it easier to filter and manage resources. If resources that are supposed to be tagged are left untagged, it can lead to reliability issues. In some use-cases, for example, scheduling EC2 instances based on tags, missing tags can prevent cost savings. 

A simple workflow can be created to identify untagged resources with the Workflow Editor. The filter node filters the resources whose tag values are absent, giving you a list of individual resources without tags. In this example, the node takes into account the name, environment, role or project keys that have no values. The custom node is used to emit this specific data into the report node, to produce a detailed report of untagged resources. The workflow shown below finds untagged RDS instances.