Admission controllers intercept requests to the Kubernetes API server. We won’t go into the details of admission controllers since the list of those supported by Kubernetes is relatively big.

We are interested only in the DefaultStorageClass which happens to be already enabled in the cluster we created with kops.

DefaultStorageClass admission controller observes creation of PersistentVolumeClaims. Through it, those that do not request any specific storage class are automatically assigned a default storage class. As a result, PersistentVolumeClaims that do not request any special storage class are bound to PersistentVolumes created from the default StorageClass. From a user’s perspective, there’s no need to care about volume types since they will be provisioned based on the default type unless they choose a specific class.