A Guide to Kubernetes Versions and Releases

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A Guide to Kubernetes Versions and Releases

Kubernetes, the industry-leading container orchestration platform, follows a consistent and predictable release cycle. Understanding this cycle, the versioning scheme, and the support policies is crucial for administrators, developers, and anyone working with Kubernetes clusters. This guide provides a comprehensive overview of Kubernetes versions and releases.

1. Versioning Scheme (Semantic Versioning)

Kubernetes adheres to the Semantic Versioning 2.0.0 specification (SemVer). A version string looks like this:

v<MAJOR>.<MINOR>.<PATCH>

  • MAJOR (X): The major version is incremented when incompatible API changes are made. This is relatively rare in Kubernetes. For instance, moving from v1 to v2 of an API would necessitate a major version bump. Kubernetes itself is still at Major version 1 (e.g., v1.28.0). Major version bumps almost always require significant changes to applications and configurations.

  • MINOR (Y): The minor version is incremented when new functionality is added in a backward-compatible manner. This is the most common type of release. A new minor version (e.g., 1.27 to 1.28) might introduce new APIs, features, and enhancements, but existing applications and configurations should continue to work without modification. However, it’s always best practice to review the release notes for deprecations and recommended updates.

  • PATCH (Z): The patch version is incremented for backward-compatible bug fixes. These fixes address security vulnerabilities, stability issues, or other problems. Patch releases (e.g., 1.28.0 to 1.28.1) are generally safe to apply without rigorous testing, although testing is always recommended.

Example:

  • v1.27.3: Major version 1, minor version 27, patch version 3.
  • v1.28.0: Major version 1, minor version 28, patch version 0 (initial release of a minor version).
  • v1.29.2-gke.1504000: Google Kubernetes Engine specific version number.

Pre-release and Build Metadata:

SemVer allows for pre-release and build metadata to be appended to the version string:

  • Pre-release: Indicates a version that is unstable and might not satisfy the intended compatibility requirements. Examples:

    • v1.29.0-alpha.1 (Alpha release – very early, highly experimental)
    • v1.29.0-beta.2 (Beta release – more stable than alpha, but still undergoing testing)
    • v1.29.0-rc.1 (Release Candidate – a final candidate for release, barring any critical issues)

  • Build Metadata: Provides additional information about the build, such as the build number or commit hash. This is often used by Kubernetes distributions.

    • v1.28.2+8e513618075845
    • v1.29.2-gke.1504000 (GKE specific version)

2. Release Cadence and Support Window

Kubernetes follows a relatively fast release cycle:

  • Minor Releases (X.Y.0): Approximately every three to four months (about three releases per year).
  • Patch Releases (X.Y.Z): As needed to address bugs and security vulnerabilities. There is generally at least one patch release per month for supported minor versions.

Support Policy:

The Kubernetes project officially supports the three most recent minor releases. This is commonly referred to as the “n-2” support policy. For example, if the latest release is 1.29, then versions 1.29, 1.28, and 1.27 are supported. Older versions (e.g., 1.26 in this example) are no longer officially supported, meaning they will not receive patch updates for bug fixes or security vulnerabilities.

Important Considerations:

  • Skew Policy: The Kubernetes control plane components (API server, scheduler, controller manager) support a skew of up to one minor version between themselves. This means the API server can be one minor version ahead or behind the other control plane components.

    • For instance, if your API server is at 1.28, the scheduler and controller manager can be at 1.27, 1.28, or 1.29.

  • Node (kubelet) Skew: The kubelet (the agent running on each node) can be up to three minor versions older than the control plane components. It cannot be newer than the control plane.

    • Example: If your API server is at 1.29, your kubelets can be at 1.26, 1.27, 1.28, or 1.29, but not 1.30.

  • kubectl Skew: The kubectl command-line tool supports a skew of one minor version in either direction from the API server.

    • Example: If your API server is at 1.28, you can use kubectl versions 1.27, 1.28, or 1.29.

3. Release Channels (for Managed Kubernetes Services)

Managed Kubernetes services (like GKE, EKS, AKS) often provide “release channels” that allow you to choose the level of stability and feature velocity you desire. These channels typically map to different Kubernetes versions and patch levels. Common channel types include:

  • Rapid: Provides the newest Kubernetes releases, potentially including alpha or beta features. Highest risk of instability.
  • Regular: A balance between new features and stability. Typically tracks the latest supported minor release.
  • Stable: Focuses on stability and long-term support. Might lag behind the latest releases by one or two minor versions.

The specific names and behaviors of release channels vary between providers. Consult your provider’s documentation for details.

4. Finding Release Information

  • Kubernetes Release Notes: The primary source of information for each release. Found on the Kubernetes GitHub repository (https://github.com/kubernetes/kubernetes/releases). Each release has detailed release notes, including changes, deprecations, and known issues.
  • Kubernetes Blog: (https://kubernetes.io/blog/) Announcements and articles about major releases and features.
  • Kubernetes Slack Channel (#sig-release): A place to discuss release-related topics with the community and maintainers.
  • Managed Kubernetes Provider Documentation: If you use a managed service (GKE, EKS, AKS, etc.), consult their documentation for details on their release processes, channels, and supported versions.
  • K8s Version Website: k8s-version.info provides a clear, up-to-date view of the currently supported and upcoming Kubernetes versions.

5. Upgrading Kubernetes

Upgrading a Kubernetes cluster is a critical operational task. The process generally involves:

  1. Review Release Notes: Thoroughly read the release notes for the target version and all intermediate versions. Pay close attention to deprecations, API changes, and known issues.
  2. Test in a Staging Environment: Always test upgrades in a non-production environment that mirrors your production cluster.
  3. Backup: Ensure you have a reliable backup of your cluster’s etcd data and any persistent volumes.
  4. Upgrade Control Plane: Upgrade the control plane components (API server, scheduler, controller manager) first.
  5. Upgrade Nodes: Upgrade the kubelets on your worker nodes. This often involves draining and cordoning nodes.
  6. Update Add-ons and Clients: Update any cluster add-ons (e.g., networking plugins, monitoring tools) and client tools (kubectl) to compatible versions.
  7. Post-Upgrade Testing: After the upgrade, perform thorough testing to ensure your applications are functioning correctly.

Important Upgrade Notes:

  • Skipping Minor Versions: Generally, you should upgrade one minor version at a time (e.g., 1.27 to 1.28, then 1.28 to 1.29). Skipping minor versions (e.g., 1.27 directly to 1.29) is not recommended and not officially supported by the Kubernetes project. It can lead to compatibility issues and unexpected behavior.
  • Automated Upgrades: Managed Kubernetes services often provide automated upgrade features, simplifying the upgrade process. However, always understand the implications and test the upgrade process thoroughly.
  • Rolling Updates vs. Blue/Green Deployments: Consider using blue/green deployments for critical clusters, where you create a new cluster with the target version and gradually switch traffic.

Conclusion

Understanding Kubernetes versions and releases is crucial for maintaining a stable, secure, and up-to-date containerized environment. By following the guidelines in this article, you can effectively manage your Kubernetes clusters and take advantage of the latest features and improvements. Remember to always consult the official Kubernetes documentation and release notes for the most accurate and up-to-date information.

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