volume_binding_mode.md

title	VolumeBindingMode
authors	k8s sig-storage authors
owners	k8s sig-storage authors
creation-date	2021-06-16
last-updated	2021-06-16
status	Implemented

StorageClass VolumeBindingMode

Table of Contents

• StorageClass VolumeBindingMode
  • Table of Contents
  • Summary
  • Motivation
    • Goals
  • Proposal
    • Implementation Details
    • Usage Details
    • Test Plan
  • Graduation Criteria
  • Drawbacks
  • Alternatives

Summary

This proposal points out workflow details to support volume binding modes.

Motivation

Goals

• As a user, I should be able to provision volume before deploying an application.
• As a user, I should be able to provision volume only when an application is requested.

Proposal

Implementation Details

LVM-LocalPV doesn't have any direct dependency over volumebinding modes moreover these are standard Kubernetes storageclass option. For more information about workflow is available here.

LVM-LocalPV honours both types of VolumeBindingModes Immediate & WaitForFirstConsumer.

• Configuring Immediate informs Kubernetes volume provisioning should be instantiated right after creation of PersistentVolumeClaim(PVC).
• Configuring WaitForFirstConsumer inform Kubernetes volume provisioning should be only after availability of consumer.

Note: If VolumeBindingMode is unspecified then defaults to Immediate mode.

Usage Details

• User/Admin can specify type of binding mode according to their usecases:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: openebs-lvm
provisioner: local.csi.openebs.io
parameters:
  storage: "lvm"
  vgpattern: "lvmvg.*"
volumeBindingMode: WaitForFirstConsumer     ## It can also replaced by Immediate volume binding mode depends on use case.

Test Plan

• Provision volume with immediate binding mode and verify that volume should get provisioned.
• Provision volume with delayed binding mode and verify that volume should remain in pending state till application deployed on volume.
• Provision application with delayed volume binding mode and verify whether pod is scheduled on a node where maximum capacity is available.

Graduation Criteria

All testcases mentioned in Test Plan section need to be automated

Drawbacks

NA

Alternatives

NA