Blog post about cgroup v1 support moving to maintenance mode / KEP-4569

Signed-off-by: Harshal Patil <harpatil@redhat.com>

content/en/blog/_posts/2024-08-15-moving-cgroup-v1-support-maintenance-mode-kubernetes-1-31.md

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+---
+layout: blog
+title: "Moving cgroup v1 Support into Maintenance Mode in Kubernetes 1.31"
+date: 2024-08-15
+slug: moving-cgroup-v1-support-maintenance-mode-kubernetes-1-31
+author: Harshal Patil
+---
+
+As Kubernetes continues to evolve and adapt to the changing landscape of
+container orchestration, the community has decided to move cgroup v1 support
+into maintenance mode in v1.31. This shift aligns with the broader industry's
+move towards cgroup v2, offering improved functionality, scalability, and
+a more consistent interface. But before we delve into what this means for
+Kubernetes, let's take a step back and understand what cgroups are and their
+significance in Linux and Kubernetes.
+
+## Understanding cgroups
+
+[Control groups](https://man7.org/linux/man-pages/man7/cgroups.7.html), or
+cgroups, are a Linux kernel feature that allows the allocation, prioritization,
+denial, and management of system resources (such as CPU, memory, disk I/O,
+and network bandwidth) among processes. This functionality is crucial for
+maintaining system performance and ensuring that no single process can
+monopolize system resources, which is especially important in multi-tenant
+environments.
+
+There are two versions of cgroups:
+[v1](https://docs.kernel.org/admin-guide/cgroup-v1/index.html) and
+[v2](https://docs.kernel.org/admin-guide/cgroup-v2.html). While cgroup v1
+provided sufficient capabilities for resource management, it had limitations
+that led to the development of cgroup v2. Cgroup v2 offers a more unified
+and consistent interface and better resource control features.
+
+## Cgroups in Kubernetes Kubernetes, a leading container orchestration
+
+platform, relies heavily on cgroups to manage and isolate the resources
+consumed by containers running in pods. Each container in Kubernetes is
+placed in its own cgroup, which allows Kubernetes to enforce resource limits,
+monitor usage, and ensure fair resource distribution among all containers.
+
+### How Kubernetes Uses cgroups:
+
+* **Resource Allocation**: Ensures that containers do not exceed their
+allocated CPU and memory limits.
+* **Isolation**: Isolates containers from each other to prevent resource
+contention.
+* **Monitoring**: Tracks resource usage for each container to provide
+insights and metrics.
+
+## Transitioning to Cgroup v2
+
+The Linux community has been focusing on cgroup v2 for new features and
+improvements. Major Linux distributions and projects like systemd are
+transitioning towards cgroup v2, which provides several benefits over cgroup
+v1, such as Unified Hierarchy, Improved Interface, Better Resource Control etc.
+
+Given these advantages, Kubernetes is also making the move to embrace cgroup
+v2 more fully. However, this transition needs to be handled carefully to avoid
+disrupting existing workloads and to provide a smooth migration path for users.
+
+## Moving cgroup v1 Support into Maintenance Mode
+
+### What Does Maintenance Mode Mean?
+
+When cgroup v1 is placed into maintenance mode in Kubernetes, it means that:
+
+1. **Feature Freeze**: No new features will be added to cgroup v1 support.
+2. **Security Fixes**: Critical security fixes will still be provided.
+3. **Best-Effort Bug Fixes**: Major bugs may be fixed if feasible, but some
+issues might remain unresolved.
+
+### Why Move to Maintenance Mode?
+
+The move to maintenance mode is driven by the need to stay in line with the
+broader ecosystem and to encourage the adoption of cgroup v2, which offers
+better performance, security, and usability. By transitioning cgroup v1 to
+maintenance mode, Kubernetes can focus on enhancing support for cgroup v2
+and ensure it meets the needs of modern workloads. It's important to note
+that maintenance mode does not mean deprecation; cgroup v1 will continue to
+receive critical security fixes and major bug fixes as needed.
+
+## Impact on Users
+
+Users currently relying on cgroup v1 are highly encouraged to plan for the
+transition to cgroup v2. This transition involves:
+
+1. **Upgrading Systems**: Ensuring that the underlying operating systems and
+container runtimes support cgroup v2.
+2. **Testing Workloads**: Verifying that workloads and applications function
+correctly with cgroup v2.
+
+## Further reading
+
+- [Cgroup v2 in
+Kubernetes](https://kubernetes.io/docs/concepts/architecture/cgroups/)