Below you fill find the bucket of cost that's the Container Cost Allocation feature accounts for when allocating cost based on utilization.
AWS (EKS / self managed)
For AWS, we include cost for any any Nodes (EC2 instances) that were present in the cluster during the time queried, as well as any attached EBS volumes. Currently PVCs aren't taken into account for allocation.
For GKE, we include cost for any billing line items that have cluster labels with 'key: gke-cluster', and a value of any cluster name Cloudability is collecting utilization data for. This also assumes you have set up a tag mapping in Cloudability for that label key. Typically this will include GCP Compute Engine costs at a minimum.
For Azure, we include any resources under the Resource Group identified in the list of nodes present in the cluster during the time queried. Typically this includes Azure Compute.