---
layout: blog
title: "Kubernetes 1.29: Single Pod Access Mode for PersistentVolumes Graduates to Stable"
date: 2023-12-18
slug: read-write-once-pod-access-mode-ga
author: >
  Chris Henzie (Google)
---

With the release of Kubernetes v1.29, the `ReadWriteOncePod` volume access mode
has graduated to general availability: it's part of Kubernetes' stable API. In
this blog post, I'll take a closer look at this access mode and what it does.

## What is `ReadWriteOncePod`?

`ReadWriteOncePod` is an access mode for
[PersistentVolumes](/docs/concepts/storage/persistent-volumes/#persistent-volumes) (PVs)
and [PersistentVolumeClaims](/docs/concepts/storage/persistent-volumes/#persistentvolumeclaims) (PVCs)
introduced in Kubernetes v1.22. This access mode enables you to restrict volume
access to a single pod in the cluster, ensuring that only one pod can write to
the volume at a time. This can be particularly useful for stateful workloads
that require single-writer access to storage.

For more context on access modes and how `ReadWriteOncePod` works read
[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)
in the _Introducing Single Pod Access Mode for PersistentVolumes_ article from 2021.

## How can I start using `ReadWriteOncePod`?

The `ReadWriteOncePod` volume access mode is available by default in Kubernetes
versions v1.27 and beyond. In Kubernetes v1.29 and later, the Kubernetes API
always recognizes this access mode.

Note that `ReadWriteOncePod` is
[only supported for CSI volumes](/docs/concepts/storage/persistent-volumes/#access-modes),
and before using this feature, you will need to update the following
[CSI sidecars](https://kubernetes-csi.github.io/docs/sidecar-containers.html)
to these versions or greater:

- [csi-provisioner:v3.0.0+](https://github.com/kubernetes-csi/external-provisioner/releases/tag/v3.0.0)
- [csi-attacher:v3.3.0+](https://github.com/kubernetes-csi/external-attacher/releases/tag/v3.3.0)
- [csi-resizer:v1.3.0+](https://github.com/kubernetes-csi/external-resizer/releases/tag/v1.3.0)

To start using `ReadWriteOncePod`, you need to create a PVC with the
`ReadWriteOncePod` access mode:

```yaml
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: single-writer-only
spec:
  accessModes:
  - ReadWriteOncePod # Allows only a single pod to access single-writer-only.
  resources:
    requests:
      storage: 1Gi
```

If your storage plugin supports
[Dynamic provisioning](/docs/concepts/storage/dynamic-provisioning/), then
new PersistentVolumes will be created with the `ReadWriteOncePod` access mode
applied.

Read [Migrating existing PersistentVolumes](/blog/2021/09/13/read-write-once-pod-access-mode-alpha/#migrating-existing-persistentvolumes)
for details on migrating existing volumes to use `ReadWriteOncePod`.

## How can I learn more?

Please see the blog posts [alpha](/blog/2021/09/13/read-write-once-pod-access-mode-alpha),
[beta](/blog/2023/04/20/read-write-once-pod-access-mode-beta), and
[KEP-2485](https://github.com/kubernetes/enhancements/blob/master/keps/sig-storage/2485-read-write-once-pod-pv-access-mode/README.md)
for more details on the `ReadWriteOncePod` access mode and motivations for CSI
spec changes.

## How do I get involved?

The [Kubernetes #csi Slack channel](https://kubernetes.slack.com/messages/csi)
and any of the standard
[SIG Storage communication channels](https://github.com/kubernetes/community/blob/master/sig-storage/README.md#contact)
are great methods to reach out to the SIG Storage and the CSI teams.

Special thanks to the following people whose thoughtful reviews and feedback helped shape this feature:

* Abdullah Gharaibeh (ahg-g)
* Aldo Culquicondor (alculquicondor)
* Antonio Ojea (aojea)
* David Eads (deads2k)
* Jan Šafránek (jsafrane)
* Joe Betz (jpbetz)
* Kante Yin (kerthcet)
* Michelle Au (msau42)
* Tim Bannister (sftim)
* Xing Yang (xing-yang)

If you’re interested in getting involved with the design and development of CSI
or any part of the Kubernetes storage system, join the
[Kubernetes Storage Special Interest Group](https://github.com/kubernetes/community/tree/master/sig-storage) (SIG).
We’re rapidly growing and always welcome new contributors.