Initial draft of blog post for in-place pod resize feature

Author: vinaykul

content/en/blog/_posts/2022-10-21-in-place-pod-resize-alpha.md

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+---
+layout: blog
+title: "Kubernetes 1.27: In-place Resource Resize for Kubernetes Pods (alpha)"
+date: 2023-04-04
+slug: in-place-pod-resize-alpha
+---
+
+**Author:** Vinay Kulkarni
+
+Kubernetes v1.27 brings a new alpha feature that allows users to resize CPU
+and memory resources allocated to their pod without restarting them. The
+`resources` field in pod's containers are now mutable for `cpu` and `memory`
+resources. Additionally, a new `restartPolicy` for resize gives users control
+over how their containers are handled during resize.
+
+Kubernetes gets the actual CPU and memory requests and limits enforced on the
+containers via an API call to the container runtime, and hence need support
+from container runtimes. The CRI (Container Runtime Interface) API changes
+for this feature were merged in v1.25 release.
+
+## What's new in 1.27?
+
+Besides the aforementioned resize policy in the pod's spec, a new field named
+`allocatedResources` was added to `containerStatuses` in the pod's status. This
+field reflects the resources allocated to the pod's containers by the node.
+
+In addition, a new field called `resources` was added to the container's status.
+This field reflects the actual resource requests and limits that are configured
+on the running containers as reported by the container runtime.
+
+Lastly, a new field named `resize` was added to the pod's status to show the
+status of the last requested resize. A value of `Proposed` is an acknowledgement
+of the requested resize and indicates that request was validated and recorded. A
+value of `InProgress` indicates that the node has accepted the resize request
+and is in the process of applying the resize request to the pod's containers.
+A value of `Deferred` means that the requested resize cannot be granted at this
+time, and the node will keep retrying. The resize may be granted when other pods
+leave and free up node resources. A value of `InFeasible` is a signal that the
+node cannot accommodate the requested resize. This can happen if the requested
+resize exceeds the maximum resources the node can ever allocate for a pod.
+
+
+## When to use this feature
+
+Below are a few examples where this feature may be useful:
+- Pod is running on node but with either too much or too little resources.
+- Pods are not being scheduled do to lack of sufficient CPU or memory in a
+cluster that is under-utilized.
+- Evicting certain pods that need more resources and scheduling them on
+bigger nodes is an expensive or disruptive operation when other pods on
+the nodes can be moved.
+
+
+## How to use this feature
+
+In order to use this feature in v1.27, the `InPlacePodVerticalScaling`
+feature gate needs to be enabled.
+
+```bash
+root@vbuild:~/go/src/k8s.io/kubernetes# FEATURE_GATES=InPlacePodVerticalScaling=true ./hack/local-up-cluster.sh
+go version go1.20.2 linux/arm64
++++ [0320 13:52:02] Building go targets for linux/arm64
+    k8s.io/kubernetes/cmd/kubectl (static)
+    k8s.io/kubernetes/cmd/kube-apiserver (static)
+    k8s.io/kubernetes/cmd/kube-controller-manager (static)
+    k8s.io/kubernetes/cmd/cloud-controller-manager (non-static)
+    k8s.io/kubernetes/cmd/kubelet (non-static)
+...
+...
+Logs:
+  /tmp/etcd.log
+  /tmp/kube-apiserver.log
+  /tmp/kube-controller-manager.log
+
+  /tmp/kube-proxy.log
+  /tmp/kube-scheduler.log
+  /tmp/kubelet.log
+
+To start using your cluster, you can open up another terminal/tab and run:
+
+  export KUBECONFIG=/var/run/kubernetes/admin.kubeconfig
+  cluster/kubectl.sh
+
+Alternatively, you can write to the default kubeconfig:
+
+  export KUBERNETES_PROVIDER=local
+
+  cluster/kubectl.sh config set-cluster local --server=https://localhost:6443 --certificate-authority=/var/run/kubernetes/server-ca.crt
+  cluster/kubectl.sh config set-credentials myself --client-key=/var/run/kubernetes/client-admin.key --client-certificate=/var/run/kubernetes/client-admin.crt
+  cluster/kubectl.sh config set-context local --cluster=local --user=myself
+  cluster/kubectl.sh config use-context local
+  cluster/kubectl.sh
+
+```
+
+
+## Example Use Cases
+
+### Cloud-based Development Environment
+
+In this scenario, a developer or development teams write their code locally
+but build and test the code in Kubernetes pods that with consistent configs.
+Such pods need minimal resources when the user is writing code, but need
+significantly more CPU and memory when the user builds the code or runs a
+battery of tests. This use case can leverage in-place pod resize feature
+(with a help from eBPF) to quickly resize the pod's resources and avoid
+kernel OOM (out of memory) killer from terminating the user's processes.
+
+This [KubeCon North America 2022 conference talk](https://www.youtube.com/watch?v=jjfa1cVJLwc)
+illustrates the use case.
+
+### Java processes initialization CPU requirements
+
+Some Java applications may need significantly more CPU during initialization
+than what is needed during normal process running times. If such
+applications specify CPU requests and limits suited for normal operation,
+they may suffer very long startup times. Such pods can request higher CPU
+values at the time of pod creation, and can resize down to normal running
+needs once the application has finished initializing.
+
+
+## References
+
+TBD-placeholder
+