Access modes
- Docker & Kubernetes course
- Advanced
- Lesson 34/70
- 4 min
Learn ReadWriteOnce, ReadOnlyMany and ReadWriteMany.
Access modes
Access modes say how a disk can be mounted at the same time:
ReadWriteOnce(RWO): a single node reads and writes. Cloud block disks (EBS, PD) are like this.ReadOnlyMany(ROX): many nodes only read.ReadWriteMany(RWX): many nodes read and write; file systems like NFS, CephFS and EFS are needed.ReadWriteOncePod(RWOP): a single pod reads and writes.
$ kubectl get pv -o custom-columns=AD:.metadata.name,MOD:.spec.accessModes
AD MOD
nfs-pv [ReadWriteMany]
pvc-9c1d [ReadWriteOnce]The RWO trap
Using an RWO PVC in a multi-replica Deployment is a common mistake: if the replicas land on different nodes, the second can't attach the disk. Solutions: a separate disk per replica (StatefulSet), RWX storage, or moving the data to object storage (S3):
Warning FailedAttachVolume Multi-Attach error for volume "pvc-9c1d…"
Volume is already exclusively attached to one node and can't be attached to anotherPractice A shared upload area
Write a PersistentVolumeClaim YAML: name yuklemeler; ReadWriteMany under accessModes; storageClassName: nfs; resources.requests.storage: 20Gi.
Starter code
# buraya yazSample solution
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: yuklemeler
spec:
accessModes:
- ReadWriteMany
storageClassName: nfs
resources:
requests:
storage: 20GiExpected output
persistentvolumeclaim/yuklemeler created NAME STATUS CAPACITY ACCESS MODES STORAGECLASS yuklemeler Bound 20Gi RWX nfs
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which mode is needed for 3 web pods on different nodes to write to the same upload folder?
- ReadOnlyMany
- ReadWriteOncePod
- ReadWriteMany Correct answer
- ReadWriteOnce
Explanation: An RWO disk can't be attached to a second node; the pod stays Pending or ContainerCreating.
2 Request read-write from many nodes.
spec:
accessModes:
- ____spec:
accessModes:
- ReadWriteManyExplanation: RWX requires a shared file system.
3 Match the modes.
| Term | Meaning |
|---|---|
RWO |
One node writes |
ROX |
Many nodes read |
RWX |
Many nodes write |
RWOP |
One pod writes |