Access mode

Q: How deeply does Acing the Certified Kubernetes Administrator Exam, Second Edition cover access mode?

Distinguishes four modes, PV/PVC selection rules, and volume compatibility, without detailing storage-driver internals.

As explained in Acing the Certified Kubernetes Administrator Exam, Second Edition

An access mode is a storage configuration specifying how many pods may read from or write to a volume.

An access mode specifies how a Kubernetes volume may be mounted and whether one or multiple nodes or pods may read, write, or both. A PersistentVolume (PV) may declare multiple modes, but a PersistentVolumeClaim (PVC) selects only one. section 7.1.3

Choose the mode from the required access pattern:

ReadWriteOnce (RWO): one node mounts the volume for reading and writing. section 7.1.3
ReadOnlyMany (ROX): multiple nodes mount the volume for reading only. section 7.1.3
ReadWriteMany (RWX): multiple nodes mount the volume for reading and writing. section 7.1.3
ReadWriteOncePod (RWOP): one pod on one node mounts the volume for reading and writing. section 7.1.3

Exam-focused volume selection

Check how many nodes need access, then verify that the volume type supports the selected mode. hostPath supports only ReadWriteOnce; nfs supports ReadWriteOnce, ReadOnlyMany, and ReadWriteMany. emptyDir is temporary pod storage rather than a PV type, so access modes are unavailable. section 7.1.3 section 7.5

Table 7.1 Access modes and their short form, used in the YAML for a PV or PVC

Access mode	Short form	Description
`ReadWriteOnce`	`RWO`	Only one node can mount the volume and read and write to it.
`ReadOnlyMany`	`ROX`	Multiple nodes can mount the volume for reading only.
`ReadWriteMany`	`RWX`	Multiple nodes can mount the volume for writing and reading.
`ReadWriteOncePod`	`RWOP`	Only one pod on that one node can mount that volume for reading and writing.

Use the access-mode table to match each full mode with its YAML short form and mounting behavior. section 7.1.3

How Acing the Certified Kubernetes Administrator Exam, Second Edition covers it

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Also explained in

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Kubernetes in Action, Second EditionAn access mode is a PersistentVolume and PersistentVolumeClaim specification describing how a volume may be mounted by nodes or pods for reading and writing.
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Kubernetes for DevelopersAn access mode specifies how and by how many Pods a persistent volume may be mounted for reading and writing.

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Related concepts

readwriteonceincludes · ReadWriteOnce is a Kubernetes persistent-storage access mode allowing a volume to be mounted for read-write use by a single node.
readonlymanyincludes · ReadOnlyMany is a Kubernetes volume access mode allowing a volume to be mounted concurrently as read-only by multiple nodes or pods.
readwritemanyincludes · ReadWriteMany is a Kubernetes volume access mode allowing a volume to be mounted concurrently as read-write by multiple nodes or pods.
persistent volumeconfigures · A persistent volume is durable storage provisioned independently of an individual workload’s lifecycle, allowing data to survive workload replacement or restart.
emptydir volumecontrasts with · An emptyDir volume is a Kubernetes volume that starts empty, is available to containers in a Pod, and is deleted when the Pod leaves its node.
ReadWriteOncePodincludes · ReadWriteOncePod is a Kubernetes volume access mode allowing a volume to be mounted read-write by only one pod at a time.

This explainer was generated by Manning's knowledge graph from the text of Acing the Certified Kubernetes Administrator Exam, Second Edition. The section links point to the parts of the book it draws on.