WIP: blog: node: kubelet podresources API GA in 1.28

I'm intentionally covering multiple related enhancements with a single
blog post.

Enhancements:
- kubernetes/enhancements#606
- kubernetes/enhancements#2403
- kubernetes/enhancements#3743

Signed-off-by: Francesco Romani <fromani@redhat.com>

content/en/blog/_posts/2023-MM-DD-kubelet-podresources-api-ga.md

@@ -0,0 +1,61 @@
+---
+layout: blog
+title: 'Kubernetes v1.28: Kubelet podresources API GA'
+date: 2023-MM-DD
+slug: kubelet-podresources-api-GA
+---
+
+**Author:**
+Francesco Romani (Red Hat)
+
+The podresources API is an API served by the kubelet locally on the node, which exposes the compute resources exclusively
+allocated to containers. In Kubernetes 1.28 the API is now Generally Available.
+
+## What problem does it solve?
+
+The kubelet can allocate exclusive resources to containers, like
+[CPUs, granting exclusive access to full cores](https://github.com/kubernetes/enhancements/tree/master/keps/sig-node/3570-cpumanager)
+or [memory, either regions or hugepages](https://github.com/kubernetes/enhancements/tree/master/keps/sig-node/1769-memory-manager).
+Workloads which require high performance, or low latency (or both) leverage these features.
+The kubelet also can assign [devices to containers](https://github.com/kubernetes/enhancements/tree/master/keps/sig-node/3573-device-plugin)
+Collectively, these features which enable exclusive assignments are known as "resource managers".
+
+The podresources API was [initially proposed to enable device monitoring](https://github.com/kubernetes/enhancements/tree/master/keps/sig-node/606-compute-device-assignment#motivation).
+In order to enable monitoring agents, a key prerequisite is to enable introspection of device assignment, which is performed by the kubelet.
+Serving this purpose was the initial goal of the API. The API was initially extremely simple, with just a single function implemented, `List`,
+to  return information about the assignment of devices to containers.
+
+Without an API like podresources, the only possible option to learn about resource assignment was to read the state files the
+resource managers use. While done out of necessity, the problem with this approach is the path and the format of these file are
+both internal implementation details. Albeit very stable, the project reserves the chance to change them freely.
+Consuming the content of the state files is thus fragile and unsupported, and projects doing this are recommended to consider
+moving to podresources API or to other supported APIs.
+
+Since its inception, the podresources API increased its scope to cover other resource managers than device manager.
+In Kubernetes 1.20, the `List` API reports also CPU cores and memory regions (including hugepages); the API also
+reports the NUMA locality of the devices, while the locality of CPUs and memory can be inferred from the system.
+In kubernetes 1.21, [the API gained the `GetAllocatableResources` function](https://github.com/kubernetes/enhancements/blob/master/keps/sig-node/2403-pod-resources-allocatable-resources/README.md).
+This new API complements the existing `List` API and enables monitoring agents to determine the unallocated resources,
+thus enabling new features built on top of the podresources API like a
+[NUMA-aware scheduler plugin](https://github.com/kubernetes-sigs/scheduler-plugins/blob/master/pkg/noderesourcetopology/README.md).
+
+## Consuming the API
+
+TBD
+
+## Future enhancements
+
+For historical reasons, the podresources API has a less precise specification with respect to the other kubernetes API.
+This leads to unspecified behavior in corner cases.
+[An effort is ongoing](https://github.com/kubernetes/kubernetes/issues/119423) to rectify this state and to have a more precise specification.
+
+The [Dynamic Resource Allocation - DRA infrastructure](https://github.com/kubernetes/enhancements/tree/master/keps/sig-node/3063-dynamic-resource-allocation)
+is a major overhaul of the resource management.
+[Integration with the podresources API](https://github.com/kubernetes/enhancements/tree/master/keps/sig-node/3695-pod-resources-for-dra)
+is already ongoing.
+
+## Getting involved
+
+This feature is driven by the [SIG Node](https://github.com/Kubernetes/community/blob/master/sig-node/README.md) community.
+Please join us to connect with the community and share your ideas and feedback around the above feature and
+beyond. We look forward to hearing from you!