Upgrading Kubernetes clusters requires careful planning. While skipping versions (e.g., going from 1.28 to 1.30) may seem tempting, it can introduce unexpected issues. This post explains why sequential upgrades (1.28 → 1.29 → 1.30) are essential and offers tips for safe upgrade paths.

Why Sequential Upgrades Matter

Kubernetes releases new minor versions approximately every three months, and each version contains new features, bug fixes, and deprecations. Skipping versions may create:

  1. Compatibility Issues: API resources or features may be removed between versions.
  2. Breakage in Workloads: Controllers and workloads relying on deprecated APIs could fail.
  3. Unsupported Upgrades: Kubernetes officially supports upgrades between adjacent minor versions only.

Example: Skipping vs. Sequential Upgrades

  • Skipped Upgrade Path:
    1.28 → 1.30
    Potential issues: Unsupported APIs removed, changes in CRDs, or storage drivers breaking unexpectedly.

  • Recommended Path:
    1.28 → 1.29 → 1.30
    Sequential upgrades ensure that each change is applied incrementally, minimizing the risk of failures.

How to Plan Your Upgrade Path

  1. Review Release Notes:
    Carefully read the release notes for each version to understand what changes will affect your workloads.

  2. Test in a Staging Environment:
    Before upgrading production, apply the upgrade to a staging cluster to detect any compatibility issues early.

  3. Use kubeadm or Rancher for Version Management:
    Tools like kubeadm and Rancher simplify version upgrades by ensuring the cluster is upgraded sequentially.

  4. Backup the Cluster:
    Always take an etcd snapshot and backup YAML configurations before upgrading. Refer to KubeBackup for automated YAML exports.

Sequential Upgrade Process

Here’s a general process for sequential upgrades using kubeadm:

  1. Upgrade Control Plane to 1.29:

    kubeadm upgrade apply v1.29.0

  2. Upgrade Worker Nodes to 1.29:

    kubectl drain <node-name> --ignore-daemonsets
kubeadm upgrade node
kubectl uncordon <node-name>

  3. Test Workloads on 1.29:
    Verify that workloads are running without issues after the 1.29 upgrade.

  4. Proceed to 1.30 Upgrade:
    Follow the same process to upgrade to 1.30.0.

Best Practices for Kubernetes Upgrades

  1. Always Upgrade Sequentially:
    Even if it’s a bit more time-consuming, sequential upgrades (e.g., 1.28 → 1.29 → 1.30) prevent API and workload issues.

  2. Monitor Cluster Health Post-Upgrade:
    Use Prometheus and Grafana to monitor cluster health and detect any anomalies during the upgrade.

  3. Automate Rollbacks:
    If something goes wrong, you should be able to rollback quickly using tools like Rancher or backups from etcd snapshots.

  4. Coordinate with Application Teams:
    Inform your developers of upcoming upgrades to avoid disruptions and ensure their workloads remain compatible.

Conclusion

Skipping Kubernetes versions may seem like a shortcut, but it introduces unnecessary risks. Sequential upgrades ensure smoother transitions by addressing changes incrementally, minimizing workload disruptions, and adhering to official Kubernetes upgrade policies. With proper planning and backups, you can upgrade your cluster with confidence.