How the controller-runtime Cache Actually Works, and Why Your Controller Does Not Crash the API Server

As Kubernetes adoption has grown, the conversation has shifted beyond running containers to managing increasingly complex application lifecycles. Modern platforms support stateless web services, stateful databases, batch processing, AI workloads, and platform services. At the same time, they must remain reliable during upgrades, scaling events, and infrastructure failures. Every Kubernetes user relies on SIG Apps, whether they realize it or not. Deployments, StatefulSets, DaemonSets, Jobs, and CronJobs form the foundation of how applications are deployed, updated, scaled, and operated across the Kubernetes ecosystem. SIG Apps is focused on improving workload resilience, refining application lifecycle management, and addressing the operational challenges that emerge when applications encounter node failures, rollout disruptions, and increasingly complex infrastructure environments.

Kubernetes v1.37 promotes the PersistentVolumeClaimUnusedSinceTime feature gate to Beta (enabled by default). With this feature, the PersistentVolumeClaim (PVC) protection controller adds an Unused condition to each PVC, telling you whether any running pod currently references it — no custom tooling or cross-referencing required. For the API definition of PVC conditions, see the PersistentVolumeClaim API reference. Read on to learn how the Unused condition works and how to use it. Why track PVC usage? In large-scale Kubernetes clusters, it is common for users to create PVCs and then delete the associated pods without cleaning up the storage, because Kubernetes does not automatically delete PVCs when their pods are removed (to protect against accidental data loss). Over time, these orphaned PVCs may accumulate, silently consuming storage capacity and driving up cloud costs.

Kubernetes v1.37 brings important storage security features: emptyDir permission modes and bind mount options. They help application programmers and security professionals implement rigorous security policies, for example, prohibiting deletion of files across containers or execution of arbitrary binaries from writable volumes, directly in Kubernetes without any complicated circumvention. Linux storage and permission fundamentals Before diving into the new Kubernetes features, let us briefly review the low-level Linux security mechanisms that make them possible. Bind mount flags When Linux mounts or remounts a directory, Virtual File System (VFS) flags control what actions are permitted on that filesystem: noexec: Do not permit direct execution of any binaries on the mounted filesystem. nosuid: Do not allow set-user-identifier or set-group-identifier bits to take effect.

With the release of Kubernetes v1.37, the Pod-Level Resource Managers feature has graduated to Beta status (disabled by default)! First introduced as an Alpha feature in Kubernetes v1.36, this enhancement builds on Pod-Level Resources by equipping Kubelet's Topology Manager, CPU Manager, and Memory Manager to use Pod-level resource declarations (.spec.resources) directly when making hardware placement decisions. Bringing pod-level resources to node managers Before this feature, obtaining exclusive NUMA-aligned CPU cores or memory for latency-critical applications forced cluster operators into an all-or-nothing choice: assign integer resource requests to every container in the Pod, or forfeit exclusive NUMA alignment entirely.

Memory QoS has graduated to Beta in Kubernetes v1.37 and is now enabled by default. On Linux nodes running cgroup v2, the feature uses the memory controller to give the kernel better guidance on how to treat container memory. It was first introduced as Alpha in v1.22, and expanded in v1.36 with tiered memory reservation. This post covers what changed in v1.37, what the Beta promotion means for cluster operators, and how to configure the feature. What changed in v1.37Memory QoS is Beta and enabled by default The MemoryQoS feature gate is now Beta in v1.37. This means every v1.37 kubelet has the feature gate turned on without any configuration change. Turning on the feature by default is safe because the default kubelet configuration does not enable memory throttling or memory reservation.

Changed Block Tracking (CBT) support for CSI drivers shipped as Alpha in September 2025. With the March 2026 v1.0.0 release of the external-snapshot-metadata project, the feature moved to Beta. If you aren't yet familiar with changed block tracking for storage in Kubernetes, the Alpha announcement covers the motivation, the three primary components (the CSI SnapshotMetadata gRPC service, the SnapshotMetadataService CRD, and the external-snapshot-metadata sidecar), and a walkthrough of how to use the API. CBT currently applies to block volumes; file-volume and network file-share changed-list tracking is not covered by this feature. This post focuses on what is different in Beta. What's new in Beta The main change in that release was the promotion of the SnapshotMetadataService CRD from v1alpha1 to v1beta1.