The many types of storage in kubernetes - and why we have them

John Griffith of Red Hat at the June 2019 Kubernetes Colorado Meetup

Introduction to K8s Storage Concepts

Volumes

• early, simple implementation
• storage was external
  • pre-provisioned attachable storage
    • iSCSI
    • EBS
    • NFS
    • ceph
• the user request for volumes was included in the connection info
• kubelet attaches volume to node pod is running on and bind-mounts it

PVs and PVCs

• volumes worked, but they were ugly because users had to know details about storage and how to consume it
• the abstraction begins!
  • the admin creates a PV and configures them in k8s
  • pvs are storage pools that users can request volumes from
  • K8s PV controller tries to allocate from available pools

Kubernetes Dynamic Provisioning

• the admin no longer has to provision
• introduce StorageClass to indicate 'what' storage pool to allocate PVs from
• marked stable in kubernetes version 1.6

Provisioners

• buckle up.
• different use cases warrant different types of storage
• storage vendors start to realize K8s is hot
• everone wants a provisioner for their storage
• lots of bloat

External Provisioners

• make provisioners an add-on
• everyone has to specialize in vendor-specific provisioners

Flex Volumes

• provided a framework to easily create an external provisioner
• could be as simple as a bash script that was loaded on the cluster

CSI

• container storage interface
• goal of the group: design an interace to specify all the operation we will need
• provide a contract to bind the container orchestrator (whatever comes after kubernetes)
• prescribe how to create a plugin for your storage
• keep the provisioners out of the kubernetes source
• provide a spec for storage plugins to work on various container platforms
• defined and built by the community
• see https://kubernetes-csi.github.io/