106 lines
4.4 KiB
Markdown
106 lines
4.4 KiB
Markdown
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---
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layout: blog
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title: "Kubernetes 1.27: Single Pod Access Mode for PersistentVolumes Graduates to Beta"
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date: 2023-04-20
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slug: read-write-once-pod-access-mode-beta
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---
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**Author:** Chris Henzie (Google)
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With the release of Kubernetes v1.27 the ReadWriteOncePod feature has graduated
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to beta. In this blog post, we'll take a closer look at this feature, what it
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does, and how it has evolved in the beta release.
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## What is ReadWriteOncePod?
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ReadWriteOncePod is a new access mode for
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[PersistentVolumes](/docs/concepts/storage/persistent-volumes/#persistent-volumes) (PVs)
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and [PersistentVolumeClaims](/docs/concepts/storage/persistent-volumes/#persistentvolumeclaims) (PVCs)
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introduced in Kubernetes v1.22. This access mode enables you to restrict volume
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access to a single pod in the cluster, ensuring that only one pod can write to
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the volume at a time. This can be particularly useful for stateful workloads
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that require single-writer access to storage.
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For more context on access modes and how ReadWriteOncePod works read
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[What are access modes and why are they important?](/blog/2021/09/13/read-write-once-pod-access-mode-alpha/#what-are-access-modes-and-why-are-they-important)
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in the _Introducing Single Pod Access Mode for PersistentVolumes_ article from 2021.
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## Changes in the ReadWriteOncePod beta
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The ReadWriteOncePod beta adds support for
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[scheduler preemption](/docs/concepts/scheduling-eviction/pod-priority-preemption/)
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of pods using ReadWriteOncePod PVCs.
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Scheduler preemption allows higher-priority pods to preempt lower-priority pods,
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so that they can start running on the same node. With this release, pods using
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ReadWriteOncePod PVCs can also be preempted if a higher-priority pod requires
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the same PVC.
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## How can I start using ReadWriteOncePod?
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With ReadWriteOncePod now in beta, it will be enabled by default in cluster
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versions v1.27 and beyond.
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Note that ReadWriteOncePod is
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[only supported for CSI volumes](/docs/concepts/storage/persistent-volumes/#access-modes).
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Before using this feature you will need to update the following
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[CSI sidecars](https://kubernetes-csi.github.io/docs/sidecar-containers.html)
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to these versions or greater:
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- [csi-provisioner:v3.0.0+](https://github.com/kubernetes-csi/external-provisioner/releases/tag/v3.0.0)
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- [csi-attacher:v3.3.0+](https://github.com/kubernetes-csi/external-attacher/releases/tag/v3.3.0)
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- [csi-resizer:v1.3.0+](https://github.com/kubernetes-csi/external-resizer/releases/tag/v1.3.0)
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To start using ReadWriteOncePod, create a PVC with the ReadWriteOncePod access mode:
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```yaml
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kind: PersistentVolumeClaim
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apiVersion: v1
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metadata:
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name: single-writer-only
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spec:
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accessModes:
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- ReadWriteOncePod # Allow only a single pod to access single-writer-only.
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resources:
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requests:
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storage: 1Gi
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```
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If your storage plugin supports
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[dynamic provisioning](/docs/concepts/storage/dynamic-provisioning/),
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new PersistentVolumes will be created with the ReadWriteOncePod access mode applied.
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Read [Migrating existing PersistentVolumes](/blog/2021/09/13/read-write-once-pod-access-mode-alpha/#migrating-existing-persistentvolumes)
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for details on migrating existing volumes to use ReadWriteOncePod.
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## How can I learn more?
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Please see the [alpha blog post](/blog/2021/09/13/read-write-once-pod-access-mode-alpha)
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and [KEP-2485](https://github.com/kubernetes/enhancements/blob/master/keps/sig-storage/2485-read-write-once-pod-pv-access-mode/README.md)
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for more details on the ReadWriteOncePod access mode and motivations for CSI spec changes.
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## How do I get involved?
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The [Kubernetes #csi Slack channel](https://kubernetes.slack.com/messages/csi)
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and any of the standard
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[SIG Storage communication channels](https://github.com/kubernetes/community/blob/master/sig-storage/README.md#contact)
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are great mediums to reach out to the SIG Storage and the CSI teams.
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Special thanks to the following people whose thoughtful reviews and feedback helped shape this feature:
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* Abdullah Gharaibeh (ahg-g)
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* Aldo Culquicondor (alculquicondor)
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* Antonio Ojea (aojea)
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* David Eads (deads2k)
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* Jan Šafránek (jsafrane)
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* Joe Betz (jpbetz)
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* Kante Yin (kerthcet)
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* Michelle Au (msau42)
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* Tim Bannister (sftim)
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* Xing Yang (xing-yang)
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If you’re interested in getting involved with the design and development of CSI
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or any part of the Kubernetes storage system, join the
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[Kubernetes Storage Special Interest Group](https://github.com/kubernetes/community/tree/master/sig-storage) (SIG).
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We’re rapidly growing and always welcome new contributors.
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