August 26, 2025 - CKS Kubernetes v1.33 available

CKS now supports Kubernetes v1.33 + cgroup v2

Update CKS CKS now supports Kubernetes v1.33, bringing the latest features and security updates to your Kubernetes clusters. This release also includes cgroup v2 as the default control group version.

Overview

This release brings Kubernetes v1.33 support to CKS, and uses cgroup v2 as the default Linux control group version - with containerd 2.0 as the default Container Runtime Interface (CRI).

As of Kubernetes v1.31, cgroup v1 support has been in maintenance mode, with cgroup v2 support in Kubernetes reaching GA as of v1.25.

CoreWeave has supported cgroup v2 in beta on CKS since early 2024, with extensive testing and validation. We feel confident in recommending cgroup v2 as the default for new clusters, and we encourage users to test and validate cgroup v2 in their environments.

Note that SUNK users will require a minimum version of SUNK v6.0.0, as well as slurmConfig.cgroupConfig.CgroupPlugin: cgroup/v2 in their chart configuration to enable cgroup v2 support.

Key improvements in Kubernetes v1.33

For a detailed breakdown of all the features and enhancements available in Kubernetes v1.33, please refer to the Kubernetes v1.33: Octarine Release blog post. Some of the key improvements include:

• Official support for Sidecar containers: Stable support for the Sidecar container pattern, allowing users to run additional containers alongside their main application container in the same pod.
• Improved Pod affinity terms: Enhanced pod affinity and anti-affinity rules, using matchLabelKeys and mismatchLabelKeys fields for finer grained scheduling.
• Improved Pod topology spread skew calculation: PodTopologySpread now supports nodeAffinityPolicy and nodeTaintsPolicy fields, weighting pod spread by node affinity and taints.

Migration considerations

When upgrading to Kubernetes v1.33:

• Review the Kubernetes v1.33 changelog for detailed changes
• Review Migrating to cgroup v2 documentation to understand the implications of switching from cgroup v1 to cgroup v2
• For SUNK installations, ensure you have SUNK v6.0.0 or later and set slurmConfig.cgroupConfig.CgroupPlugin: cgroup/v2 in your chart configuration

Migration notes

CKS clusters

• Existing clusters will continue to work without changes
• New clusters can be created with Kubernetes v1.33
• Plan for upgrading existing clusters to v1.33 when ready
• Clusters upgrading from v1.32 or earlier will have cgroup v2 enabled by default on newly created nodepools