Upgrade Kubernetes on Worker Nodes

Upgrading the Kubernetes version in a cluster ensures that your infrastructure is up to date and secure. This process involves updating the Kubernetes control plane and worker nodes to a new version while also making sure that the Redpanda cluster continues to function with minimal downtime.

Prerequisites

  • A staging environment in which to test the upgrade procedure before performing it in production.

  • A running Redpanda deployment on a Kubernetes cluster.

  • Familiarity with your hosting platform (GKE, EKS, AKS, or self-hosted) and any CLI tools your platform provides, such as gcloud or eksctl.

  • Confirmation that the new version of Kubernetes is compatible with the version of Redpanda you are using. See the Helm chart requirements.

  • Upgrade the Redpanda Helm chart.

Upgrade the Redpanda Helm chart

Before upgrading Kubernetes, upgrade your Redpanda Helm chart to the latest version. Upgrading the chart ensures that older versions of Kubernetes resources are replaced by newer versions. Failing to do so might lead to Helm encountering deprecated versions during the Kubernetes upgrade, resulting in errors and potential downtime.

For example, starting in Kubernetes 1.25 and later, the v1beta1 version of the PodDisruptionBudget resource is deprecated. If you were running a previous version of Kubernetes and you performed a Helm upgrade after updating Kubernetes, Helm would carry out a 3-way merge between the desired state, the previous state, and the current state of your cluster. If your cluster’s previous state still referenced the v1beta1 resource version, Helm would fail to upgrade as this version isn’t available in your version of Kubernetes.

See Upgrade Redpanda in Kubernetes.

Minimize data loss and downtime during Kubernetes upgrades

Upgrading the Kubernetes version involves updating Kubernetes components and other dependencies, which requires node restarts. To minimize data loss and downtime during the upgrade process, you must take precautions. This section outlines essential information on how the Helm chart helps maintain high availability and what steps you can take to avoid data loss, depending on the type of storage volumes that you use.

The Helm chart provides the following features to minimize data loss and downtime during the upgrade process:

  • A Pod Disruption Budget (PDB) that limits the number of concurrently unavailable Pods within the StatefulSet, ensuring the desired level of redundancy. Hosting platforms such as EKS and GKE respect the PDB during node upgrades, providing a safer upgrade process. For the default PDB, see budget.maxUnavailable in the Helm chart.

  • Graceful shutdowns for all Pods within the StatefulSet to reduce potential data corruption.

Depending on your type of storage volume, you must take precautions to ensure your deployment can tolerate node restarts and avoid data loss:

PersistentVolumes

If you use PersistentVolumes (PV) to store the Redpanda data directory, take the following precautions:

  • Verify compatibility between your storage classes and PersistentVolumes (PV) configurations with the new Kubernetes version.

  • If you use local PVs, your data is bound to the node where the PV is created, risking data loss during node deletions or failures. To minimize the risk of data loss, see Best practices for local storage.

    Data in remote PVs remains safe during upgrades, as the PV is decoupled from the worker nodes.

hostPath

Data in hostPath volumes is bound to a specific node, risking data loss during node deletions or failures. To minimize the risk of data loss, see Best practices for local storage.

emptyDir

Data in emptyDir volumes is ephemeral and will be lost when the container is terminated or the node is deleted. To minimize the risk of data loss, see Best practices for local storage.

Best practices for local storage

When using local storage (local PV, hostPath, or emptyDir), data loss can occur during Kubernetes upgrades. To minimize the risk of data loss, follow these best practices before you upgrade:

  • Replicate all topics: If you have topics with a replication factor of 1, temporarily increase the replication factor of those topics before you upgrade. A replication factor of at least 2 ensures that even if one node experiences data loss, you can still recover the data from a replica on another node. See rpk topic alter-config.

    rpk topic alter-config [<topic-name>,] --set replication.factor=<replication-factor>

    After increasing the replication factor, monitor for under-replicated partitions and wait until all partitions are replicated.

  • Delete PVCs: If you are using local PVs in Kubernetes version 1.26 or earlier, make sure to delete the PersistentVolumeClaims (PVC) before upgrading the worker node. Otherwise, your Pods will remain in a pending state when they are rescheduled because the PVs are bound to the node through node affinity.

    Deleting a PVC does not remove it from the system immediately. Instead, a deletionTimestamp is set on the PVC, but it will not be deleted until the associated Pod is terminated.

  • Decommission brokers: Decommission the broker on the worker node planned for an upgrade. Decommissioning helps prevent data loss by gracefully moving the broker’s topic partitions and replicas to other brokers in the cluster. See Decommission Brokers.

Upgrade Kubernetes on your hosting platform

In this section, you can find helpful resources for upgrading Kubernetes on different hosting platforms.

Before you upgrade, make sure that you’ve read the prerequisites and the section on minimizing data loss and downtime.

For all hosting platforms, you must upgrade the control plane first. Control plane components are backward-compatible with older worker node versions. Some hosting platforms may upgrade the control plane for you automatically.

Before you upgrade a worker node, make sure that it is cordoned to prevent new Pods from being scheduled on it. Then, make sure that it is drained to ensure that any running Pods are safely evicted before the upgrade. The eviction process minimizes the risk of data loss or corruption by triggering a graceful shutdown of the Pods.

After completing the upgrade process, verify the health of your Redpanda deployment and ensure that data has been retained as expected.

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