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Default Storage Class Prerequisite📜

  • Big Bang assumes the cluster you’re deploying to supports dynamic volume provisioning.
  • A Big Bang cluster should have 1 Storage Class (SC) annotated as the default SC.
  • For production deployments, it is recommended to leverage a SC that supports the creation of volumes that support ReadWriteMany Access Mode, as there are a few Big Bang add-ons, where an HA application configuration requires a storage class that supports ReadWriteMany.

How Dynamic Volume Provisioning Works in a Nut Shell📜

  • StorageClass + PersistentVolumeClaim = Dynamically Created Persistent Volume
  • A PersistentVolumeClaim that does not reference a specific SC will leverage the default SC, of which there should only be one, identified using Kubernetes annotations. Some helm charts allow a SC to be explicitly specified so that multiple SCs can be used simultaneously.

How To Check What Storage Classes Are Installed on Your Cluster📜

  • kubectl get storageclass can be used to see what storage classes are available on a cluster; the default will be marked accordingly. NOTE: You can have multiple storage classes, but you should only have one default storage class.
kubectl get storageclass
# NAME                   PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
# local-path (default)   rancher.io/local-path   Delete          WaitForFirstConsumer   false                  47h

AWS Specific Notes📜

Example AWS Storage Class Configuration📜

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: gp2
  annotations:
    storageclass.kubernetes.io/is-default-class: 'true'
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp2 #gp3 isn't supported by the in-tree plugin
  fsType: ext4
#  encrypted: 'true' #requires kubernetes nodes have IAM rights to a KMS key
#  kmsKeyId: 'arn:aws-us-gov:kms:us-gov-west-1:110518024095:key/b6bf63f0-dc65-49b4-acb9-528308195fd6'
reclaimPolicy: Retain
allowVolumeExpansion: true

AWS EBS Volumes📜

  • AWS EBS Volumes have the following limitations:
  • An EBS volume can only be attached to a single Kubernetes Node at a time, thus ReadWriteMany Access Mode isn’t supported.
  • An EBS PersistentVolume in Availability Zone (AZ) 1, cannot be mounted by a worker node in AZ2.

AWS EFS Volumes📜

  • An AWS EFS Storage Class can be installed according to the vendors docs.
  • AWS EFS Storage Class supports ReadWriteMany Access Mode.
  • AWS EFS Persistent Volumes can be mounted by worker nodes in multiple AZs.
  • AWS EFS is basically NetworkFileSystem (NFS) as a Service. NFS cons like latency apply equally to EFS, and therefore it’s not a good fit for for databases.

Azure Specific Notes📜

Azure Disk Storage Class Notes📜

  • The Kubernetes Docs offer an example Azure Disk Storage Class
  • An Azure disk can only be mounted with Access mode type ReadWriteOnce, which makes it available to one node in AKS.
  • An Azure Disk PersistentVolume in AZ1 can be mounted by a worker node in AZ2, although some additional lag is involved in such transitions.

Bare Metal/Cloud Agnostic Store Class Notes📜

NOTE: No storage class specific container images exist in IronBank at this time. * Approved IronBank Images will show up in https://registry1.dso.mil. * https://repo1.dso.mil/dsop can be used to check status of IronBank images.