Understanding Reclaim Policies for Persistent Volumes in Kubernetes
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Chapter 1: Introduction to Stateful Workloads
When it comes to managing stateful workloads within a Kubernetes cluster, challenges often arise, particularly concerning data management. The robust features of Kubernetes can pose difficulties when dealing with stateful services that depend heavily on data retention. Many of these challenges now have established solutions, especially as numerous stateful workloads—like databases and backend systems—necessitate a comprehensive understanding of various configurations, including the reclaim policy for persistent volumes.
Section 1.1: What is a Reclaim Policy?
To clarify the concept of reclaim policies, we can refer to the official Kubernetes documentation, which states:
> When a user is finished using their volume, they can remove the PVC objects from the API, which enables reclamation of the resource. The reclaim policy for a PersistentVolume indicates to the cluster what actions to take with the volume once it has been released from its claim. Presently, volumes can be set to either Retain, Recycle, or Delete.
This gives us three distinct options: Retain, Recycle, or Delete. Let’s explore the implications of each policy.
Subsection 1.1.1: Retain
Choosing to retain means that the data will persist even after the claim is removed. All policies activate only when the original PVC is deleted. Until that point, the data remains intact regardless of the policy selected.
If the retain policy is applied, the data will be safeguarded, preventing any other PVC from claiming it. An administrator will need to follow this process to reclaim the data:
- Delete the PersistentVolume.
- Manually clear the data on the corresponding storage asset.
- Manually remove the associated storage asset.
Section 1.2: Delete
Opting for the delete policy means that both the PV and its data are released as soon as the PVC is removed. This simplifies the management of your volumes but introduces a risk of data loss due to unforeseen circumstances. It's essential to remember that if you attempt to delete a PVC currently in use by a Pod, the removal will be deferred until the PVC is no longer in use to prevent data loss.
Similarly, for the PV, if an administrator deletes it while still attached to a PVC, the removal will be postponed until the PV is detached.
Section 1.3: Recycle
The recycle policy operates somewhat like the delete policy but instead of eliminating the volume, it clears the contents of the PV. Practically speaking, this policy functions similarly to executing a command like rm -rf on the storage asset. However, be aware that this policy is now deprecated; although it remains supported, you should avoid using it for new workloads.
Chapter 2: Video Insights on Persistent Volumes
The first video titled "Using Persistent Volumes and Claims in Kubernetes Cluster" dives into the essentials of managing persistent volumes and their claims, providing practical insights and guidance.
The second video, "Day 29/40 Kubernetes Volume Simplified | Persistent Volume, Persistent Volume Claim & Storage Class," offers a simplified overview of persistent volumes, their claims, and the associated storage classes, making it easier to grasp these concepts.