To migrate Kubernetes nodes to cgroup v2 safely, first verify a cgroup-v2-capable Linux distribution and kernel, then use a container runtime that supports it and configure both kubelet and the runtime with the same systemd cgroup driver. Kubernetes normally detects cgroup v2 automatically when those requirements are met. Most pods continue running unchanged, but software that reads cgroup files—monitoring agents, security tools, cAdvisor, and some language runtimes—must be checked.
Use stat -fc %T /sys/fs/cgroup/ on every node to identify the current mode, audit applications that calculate memory from cgroups, and prefer replacing or reinstalling nodes over changing the driver on an already joined node.
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What cgroup v2 changes in Kubernetes
Linux control groups (cgroups) limit and account for CPU, memory, and other resources. Kubernetes places pods and containers in that hierarchy so requests and limits can be enforced. cgroup v2 replaces the older v1 hierarchy with a unified interface and different file names, controls, and delegation rules.
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Kubernetes has treated cgroup v2 as stable since version 1.25. The Kubernetes documentation says that, when the operating system and runtime meet its requirements, “The kubelet automatically detects that the OS is running on cgroup v2 and performs accordingly with no additional configuration required.” That automatic behavior does not remove the need to align the kubelet and runtime drivers or to update software that reads cgroup files directly.
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Compatibility requirements before you migrate
Check these conditions on every Linux worker and control-plane node that will run workloads. The versions below are Kubernetes’ documented minimums or examples; packaged defaults can differ by distribution, so verify the actual installed versions.
| Component | Requirement or documented example | What to verify |
|---|---|---|
| Linux distribution | A distribution that enables cgroup v2 by default | Distribution release documentation and the mounted cgroup filesystem |
| Linux kernel | 5.8 or later | uname -r on each node |
| Container runtime | containerd 1.4 or later, or CRI-O 1.20 or later | Installed runtime version and its cgroup-driver support |
| Kubelet and runtime driver | systemd for both, as recommended for cgroup v2 |
Effective configuration, not only configuration files left on disk |
| Kubernetes release | cgroup v2 stable from Kubernetes 1.25 | Release-specific documentation for your target upgrade |
Meeting these baselines is necessary but is not a guarantee that every vendor package behaves identically. Confirm the runtime’s driver-discovery behavior and the distribution’s boot configuration before changing production nodes.
How to tell whether a node uses cgroup v1 or v2
Run this command locally on each Linux node:
stat -fc %T /sys/fs/cgroup/cgroup2fsmeans the node is using cgroup v2.tmpfsgenerally indicates a cgroup v1 hierarchy.
Record the result together with the kernel, Kubernetes, kubelet, and runtime versions. A mixed cluster is possible during a rolling migration, but each node must be internally consistent and meet the requirements of the workloads scheduled there.
A practical migration procedure
Use a staged, node-by-node process. Test the same operating-system image, runtime package, and bootstrap configuration in a non-production cluster first.
- Inventory the cluster. List every Linux node, its kernel and distribution, Kubernetes version, runtime version, current cgroup mode, and effective cgroup driver. Include dedicated monitoring and security nodes.
- Check workload dependencies. Identify DaemonSets, sidecars, admission components, and application images that read files below
/sys/fs/cgroup. Ask each vendor or project for cgroup v2 support rather than assuming a v1-compatible release will work unchanged. - Prepare the node image. Use a distribution and kernel that satisfy the documented requirements. Install a supported container runtime and configure its cgroup driver to
systemd. - Configure kubelet consistently. Set the kubelet cgroup driver to
systemdwhen automatic runtime discovery is unavailable. For kubeadm-managed clusters, the relevant configuration is aKubeletConfigurationcontainingcgroupDriver: systemd. - Validate before joining. Boot the node, run the filesystem check, inspect the runtime and kubelet logs, and confirm that both components report the same driver. Do not join a node whose driver settings are uncertain.
- Drain and replace nodes in a controlled order. Cordon the node, drain it using your normal disruption policy, remove or reinstall it with the prepared image, and then allow it to rejoin. Respect PodDisruptionBudgets and capacity limits while draining.
- Run workload and observability tests. Check pod startup, resource-limit enforcement, metrics, logging, security agents, and application memory behavior before moving to the next node.
For an already joined node, changing only one driver setting is risky. Kubernetes warns that changing the cgroup driver can prevent existing pod sandboxes from being recreated; restarting kubelet may not repair that state. Replacing the node through established automation is usually safer than an in-place driver conversion.
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Aligning kubelet and the container runtime
Kubelet and the runtime create and manage the same pod hierarchy. If one uses cgroupfs and the other uses systemd, they can place processes in incompatible paths and fail during sandbox creation or recreation. Kubernetes recommends systemd for cgroup v2.
Some newer containerd and CRI-O releases can discover the driver automatically, while older releases require explicit settings. Check the exact runtime documentation and the effective service configuration. A file containing systemd is not proof that the running process used it; verify through runtime and kubelet startup logs or the node’s reported configuration.
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cgroupDriver: systemdApply the setting through the same kubeadm or node-provisioning workflow that manages the rest of your fleet. Avoid hand-editing one node if automation will overwrite it on the next reboot.
Will cgroup v2 break existing pods?
Ordinary applications that rely on Kubernetes resource limits through the container runtime usually do not notice the migration. The risk is concentrated in software that parses cgroup files, assumes v1 paths, or infers available memory from the host instead of the container limit.
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Monitoring and security agents
Review third-party monitoring and security agents that run as DaemonSets or host processes. Standalone cAdvisor deployments need cgroup v2 support; Kubernetes identifies cAdvisor 0.43.0 or later as the compatibility example. Confirm the agent’s current documentation, then test CPU, memory, filesystem, and process metrics after migration.
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Java runtimes
Java’s container-awareness behavior depends on the vendor and release. Kubernetes lists these cgroup v2-compatible examples:
| Runtime family | Documented cgroup v2 examples |
|---|---|
| OpenJDK/HotSpot | jdk8u372, 11.0.16, and 15 or later |
| IBM Semeru | 8.0.382.0, 11.0.20.0, and 17.0.8.0 or later |
| IBM Java | 8.0.8.6 or later |
These are compatibility examples, not a substitute for the current support statement from your Java vendor. Verify that the JVM sees the pod’s memory and CPU limits rather than the node totals.
Go applications using automaxprocs
Applications using uber-go/automaxprocs should use version 1.5.1 or higher, which includes cgroup v2 support according to Kubernetes guidance. Confirm the dependency version in the built image, not merely in the source repository.
Node.js memory limits
Node.js obtains cgroup v2 memory limits through libuv starting with Node.js 20.3.0. The Node.js 18 line does not reliably detect those limits. An affected process can size its heap against host memory, then be terminated by the kernel when the pod limit is reached.
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For an affected release, set an explicit heap ceiling appropriate to the pod’s memory limit, for example:
node --max-old-space-size=1536 server.jsLeave headroom for native allocations, buffers, and the runtime itself; the value must not consume the entire Kubernetes memory limit.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Inspecting the cgroup hierarchy after migration
Under cgroup v2, systemd usually organizes Kubernetes workloads into slices and scopes. These commands help confirm placement and resource accounting:
systemctl list-units 'kube*' --type=slice
systemctl list-units 'kube*' --type=scope
systemd-cgls
systemd-cgtop
tree -L 2 -d /sys/fs/cgroup/kubepods.slice
bpftool cgroup list /sys/fs/cgroup/*The first two commands show systemd units; systemd-cgls displays the hierarchy; systemd-cgtop provides live usage; and the tree command shows the Kubernetes slice layout when that path exists. bpftool can reveal eBPF programs attached to cgroups, which is useful when a security or networking component changes behavior after the migration.
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The node reports cgroup v1 unexpectedly
- Check the distribution’s documented default and kernel boot parameters.
- Confirm that the running kernel is at least 5.8.
- Run the filesystem test again after rebooting; changing a package without rebooting does not change the mounted hierarchy.
- Verify that all nodes, not just the control plane, have been converted.
Pods fail to create or sandboxes cannot be recreated
Compare the effective kubelet and runtime drivers first. A mismatch commonly appears after an in-place edit or partial upgrade. Restore matching systemd settings and, when the node is already joined, follow the platform’s node replacement procedure instead of repeatedly restarting kubelet.
Metrics disappear or show host-sized limits
Identify which component reads cgroup files. Upgrade cAdvisor, monitoring agents, and security agents to cgroup v2-aware releases, then restart the DaemonSet so the new binary is actually running. Check both the agent logs and the values exposed for a test pod with a deliberately small memory limit.
Applications are killed for out-of-memory despite a configured limit
First confirm the pod limit and the process’s view of that limit. Node.js 18 is a known risk because it may not detect cgroup v2 memory correctly; set --max-old-space-size or move to a release with the newer libuv behavior. For Java and other runtimes, use the vendor’s cgroup v2 guidance and leave headroom for non-heap memory.
Only some nodes behave differently
Compare the cgroup filesystem result, kernel, runtime, driver, and node image across the affected and unaffected nodes. Scheduling the same test pod on each node can expose an image-specific agent or bootstrap difference. Keep a node-level inventory until the migration is complete.
cgroup v1 deprecation and Kubernetes 1.35
cgroup v1 support is release-sensitive and deprecated. A Kubernetes project article published on 2026-10-06 states that Kubernetes 1.35 defaults to refusing kubelet startup on cgroup v1 unless the failCgroupV1 setting is disabled. That behavior makes the node’s cgroup mode an upgrade prerequisite, not an optional cleanup task.
Before upgrading, read the official documentation for the exact target release, verify every Linux node, and confirm whether your runtime can discover the driver automatically. Do not carry a temporary fallback setting forward without an explicit plan to remove it.
Managed Kubernetes considerations
Managed-service providers control parts of the node image, kernel, runtime, and kubelet configuration. Ask the provider when cgroup v2 will be enabled, whether existing node pools are upgraded in place or replaced, which agent versions are supported, and whether customer workloads need changes. Apply provider-specific instructions rather than forcing host-level settings that the service may overwrite.
For self-managed or kubeadm clusters, keep the migration in infrastructure automation, test node replacement, and document the exact runtime and kubelet versions used. A successful migration is one where every node reports the intended cgroup mode, drivers match, resource limits remain enforceable, and all cgroup-reading software has been validated.
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The Bottom Line
Verify cgroup mode and kernel support on every node, align kubelet and runtime on systemd, audit cgroup-reading software, and replace rather than casually reconfigure joined nodes. With those checks completed, cgroup v2 is usually transparent to ordinary Kubernetes workloads.
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