Add blog for PersistentVolume last phase transition time

Author: RomanBednar

content/en/blog/_posts/2023-10-23-pv-last-phase-transtition-time.md

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+---
+layout: blog
+title: PersistentVolume Last Phase Transition Time in Kubernetes
+date: 2023-10-23
+slug: persistent-volume-last-phase-transition-time
+---
+
+**Author:** Roman Bednář (Red Hat)
+
+In the recent Kubernetes v1.28 release, we (SIG Storage) introduced a new alpha feature that aims to improve PersistentVolume (PV)
+storage management and help cluster administrators gain better insights into the lifecycle of PVs.
+With the addition of the `lastPhaseTransitionTime` field into the status of a PV,
+cluster administrators are now able to track the last time a PV transitioned to a different
+[phase](/docs/concepts/storage/persistent-volumes/#phase), allowing for more efficient
+and informed resource management.
+
+## Why do we need new PV field? {#why-new-field}
+
+PersistentVolumes in Kubernetes play a crucial role in providing storage resources to workloads running in the cluster.
+However, managing these PVs effectively can be challenging, especially when it comes
+to determining the last time a PV transitioned between different phases, such as
+`Pending`, `Bound` or `Released`.
+Administrators often need to know when a PV was last used or transitioned to certain
+phases; for instance, to implement retention policies, perform cleanup, or monitor storage health.
+
+In the past, Kubernetes users have faced data loss issues when using the `Delete` retain policy and had to resort to the safer `Retain` policy.
+When we planned the work to introduce the new `lastPhaseTransitionTime` field, we
+wanted to provide a more generic solution that can be used for various use cases,
+including manual cleanup based on the time a volume was last used or producing alerts based on phase transition times.
+
+## How lastPhaseTransitionTime helps
+
+Provided you've enabled the feature gate (see [How to use it](#how-to-use-it), the new `.status.lastPhaseTransitionTime` field of a PersistentVolume (PV)
+is updated every time that PV transitions from one phase to another.
+``
+Whether it's transitioning from `Pending` to `Bound`, `Bound` to `Released`, or any other phase transition, the `lastPhaseTransitionTime` will be recorded.
+For newly created PVs the phase will be set to `Pending` and the `lastPhaseTransitionTime` will be recorded as well.
+
+This feature allows cluster administrators to:
+
+1. Implement Retention Policies
+
+   With the `lastPhaseTransitionTime`, administrators can now track when a PV was last used or transitioned to the `Released` phase.
+   This information can be crucial for implementing retention policies to clean up resources that have been in the `Released` phase for a specific duration.
+   For example, it is now trivial to write a script or a policy that deletes all PVs that have been in the `Released` phase for a week.
+
+2. Monitor Storage Health
+
+   By analyzing the phase transition times of PVs, administrators can monitor storage health more effectively.
+   For example, they can identify PVs that have been in the `Pending` phase for an unusually long time, which may indicate underlying issues with the storage provisioner.
+
+## How to use it
+
+The `lastPhaseTransitionTime` field is alpha starting from Kubernetes v1.28, so it requires
+the `PersistentVolumeLastPhaseTransitionTime` feature gate to be enabled.
+
+If you want to test the feature whilst it's alpha, you need to enable this feature gate on the `kube-controller-manager` and the `kube-apiserver`.
+
+Use the `--feature-gates` command line argument:
+
+```shell
+--feature-gates="...,PersistentVolumeLastPhaseTransitionTime=true"
+```
+
+Keep in mind that the feature enablement does not have immediate effect; the new field will be populated whenever a PV is updated and transitions between phases.
+Administrators can then access the new field through the PV status, which can be retrieved using standard Kubernetes API calls or through Kubernetes client libraries.
+
+Here is an example of how to retrieve the `lastPhaseTransitionTime` for a specific PV using the `kubectl` command-line tool:
+
+```shell
+kubectl get pv <pv-name> -o jsonpath='{.status.lastPhaseTransitionTime}'
+```
+
+## Going forward
+
+This feature was initially introduced as an alpha feature, behind a feature gate that is disabled by default.
+During the alpha phase, we (Kubernetes SIG Storage) will collect feedback from the end user community and address any issues or improvements identified.
+
+Once sufficient feedback has been received, or no complaints are received the feature can move to beta.
+The beta phase will allow us to further validate the implementation and ensure its stability.
+
+At least two Kubernetes releases will happen between the release where this field graduates
+to beta and the release that graduates the field to general availability (GA). That means that
+the earliest release where this field could be generally available is Kubernetes 1.32,
+likely to be scheduled for early 2025.
+
+## Getting involved
+
+We always welcome new contributors so if you would like to get involved you can
+join our [Kubernetes Storage Special-Interest-Group](https://github.com/kubernetes/community/tree/master/sig-storage) (SIG).
+
+If you would like to share feedback, you can do so on our
+[public Slack channel](https://app.slack.com/client/T09NY5SBT/C09QZFCE5).
+If you're not already part of that Slack workspace, you can visit https://slack.k8s.io/ for an invitation.
+
+Special thanks to all the contributors that provided great reviews, shared valuable insight and helped implement this feature (alphabetical order):
+
+- Han Kang ([logicalhan](https://github.com/logicalhan))
+- Jan Šafránek ([jsafrane](https://github.com/jsafrane))
+- Jordan Liggitt ([liggitt](https://github.com/liggitt))
+- Kiki ([carlory](https://github.com/carlory))
+- Michelle Au ([msau42](https://github.com/msau42))
+- Tim Bannister ([sftim](https://github.com/sftim))
+- Wojciech Tyczynski ([wojtek-t](https://github.com/wojtek-t))
+- Xing Yang ([xing-yang](https://github.com/xing-yang))