Resize CPU and Memory Resources assigned to Containers

FEATURE STATE: Kubernetes v1.27 [alpha] (enabled by default: false)

This page assumes that you are familiar with Quality of Service for Kubernetes Pods.

This page shows how to resize CPU and memory resources assigned to containers of a running pod without restarting the pod or its containers. A Kubernetes node allocates resources for a pod based on its requests, and restricts the pod's resource usage based on the limits specified in the pod's containers.

Changing the resource allocation for a running Pod requires the InPlacePodVerticalScaling feature gate to be enabled. The alternative is to delete the Pod and let the workload controller make a replacement Pod that has a different resource requirement.

A resize request is made through the pod /resize subresource, which takes the full updated pod for an update request, or a patch on the pod object for a patch request.

For in-place resize of pod resources:

  • A container's resource requests and limits are mutable for CPU and memory resources. These fields represent the desired resources for the container.
  • The resources field in containerStatuses of the Pod's status reflects the resources allocated to the pod's containers. For running containers, this reflects the actual resource requests and limits that are configured as reported by the container runtime. For non-running containers, these are the resources allocated for the container when it starts.
  • The resize field in the Pod's status shows the status of the last requested pending resize. It can have the following values:
    • Proposed: This value indicates that a pod was resized, but the Kubelet has not yet processed the resize.
    • InProgress: This value indicates that the node has accepted the resize request and is in the process of applying it to the pod's containers.
    • Deferred: This value 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 are removed and free up node resources.
    • 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.
    • "": An empty or unset value indicates that the last resize completed. This should only be the case if the resources in the container spec match the resources in the container status.

If a node has pods with an incomplete resize, the scheduler will compute the pod requests from the maximum of a container's desired resource requests, and it's actual requests reported in the status.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

Your Kubernetes server must be at or later than version 1.27. To check the version, enter kubectl version.

The InPlacePodVerticalScaling feature gate must be enabled for your control plane and for all nodes in your cluster.

Container Resize Policies

Resize policies allow for a more fine-grained control over how pod's containers are resized for CPU and memory resources. For example, the container's application may be able to handle CPU resources resized without being restarted, but resizing memory may require that the application hence the containers be restarted.

To enable this, the Container specification allows users to specify a resizePolicy. The following restart policies can be specified for resizing CPU and memory:

  • NotRequired: Resize the container's resources while it is running.
  • RestartContainer: Restart the container and apply new resources upon restart.

If resizePolicy[*].restartPolicy is not specified, it defaults to NotRequired.

Below example shows a Pod whose Container's CPU can be resized without restart, but resizing memory requires the container to be restarted.

apiVersion: v1
kind: Pod
metadata:
  name: qos-demo-5
  namespace: qos-example
spec:
  containers:
  - name: qos-demo-ctr-5
    image: nginx
    resizePolicy:
    - resourceName: cpu
      restartPolicy: NotRequired
    - resourceName: memory
      restartPolicy: RestartContainer
    resources:
      limits:
        memory: "200Mi"
        cpu: "700m"
      requests:
        memory: "200Mi"
        cpu: "700m"

Limitations

In-place resize of pod resources currently has the following limitations:

  • Only CPU and memory resources can be changed.
  • Pod QoS Class cannot change. This means that requests must continue to equal limits for Guaranteed pods, Burstable pods cannot set requests and limits to be equal for both CPU & memory, and you cannot add resource requirements to Best Effort pods.
  • Init containers and Ephemeral Containers cannot be resized.
  • Resource requests and limits cannot be removed once set.
  • A container's memory limit may not be reduced below its usage. If a request puts a container in this state, the resize status will remain in InProgress until the desired memory limit becomes feasible.
  • Windows pods cannot be resized.

Create a pod with resource requests and limits

You can create a Guaranteed or Burstable Quality of Service class pod by specifying requests and/or limits for a pod's containers.

Consider the following manifest for a Pod that has one Container.

pods/qos/qos-pod-5.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: qos-demo-5
  namespace: qos-example
spec:
  containers:
  - name: qos-demo-ctr-5
    image: nginx
    resources:
      limits:
        memory: "200Mi"
        cpu: "700m"
      requests:
        memory: "200Mi"
        cpu: "700m"

Create the pod in the qos-example namespace:

kubectl create namespace qos-example
kubectl create -f https://k8s.io/examples/pods/qos/qos-pod-5.yaml

This pod is classified as a Guaranteed QoS class requesting 700m CPU and 200Mi memory.

View detailed information about the pod:

kubectl get pod qos-demo-5 --output=yaml --namespace=qos-example

Also notice that the values of resizePolicy[*].restartPolicy defaulted to NotRequired, indicating that CPU and memory can be resized while container is running.

spec:
  containers:
    ...
    resizePolicy:
    - resourceName: cpu
      restartPolicy: NotRequired
    - resourceName: memory
      restartPolicy: NotRequired
    resources:
      limits:
        cpu: 700m
        memory: 200Mi
      requests:
        cpu: 700m
        memory: 200Mi
...
  containerStatuses:
...
    name: qos-demo-ctr-5
    ready: true
...
    resources:
      limits:
        cpu: 700m
        memory: 200Mi
      requests:
        cpu: 700m
        memory: 200Mi
    restartCount: 0
    started: true
...
  qosClass: Guaranteed

Updating the pod's resources

Let's say the CPU requirements have increased, and 0.8 CPU is now desired. This may be specified manually, or determined and programmatically applied by an entity such as VerticalPodAutoscaler (VPA).

Now, patch the Pod's Container with CPU requests & limits both set to 800m:

kubectl -n qos-example patch pod qos-demo-5 --subresource resize --patch '{"spec":{"containers":[{"name":"qos-demo-ctr-5", "resources":{"requests":{"cpu":"800m"}, "limits":{"cpu":"800m"}}}]}}'

Query the Pod's detailed information after the Pod has been patched.

kubectl get pod qos-demo-5 --output=yaml --namespace=qos-example

The Pod's spec below reflects the updated CPU requests and limits.

spec:
  containers:
    ...
    resources:
      limits:
        cpu: 800m
        memory: 200Mi
      requests:
        cpu: 800m
        memory: 200Mi
...
  containerStatuses:
...
    resources:
      limits:
        cpu: 800m
        memory: 200Mi
      requests:
        cpu: 800m
        memory: 200Mi
    restartCount: 0
    started: true

Observe that the resources in the containerStatuses have been updated to reflect the new desired CPU requests. This indicates that node was able to accommodate the increased CPU resource needs, and the new CPU resources have been applied. The Container's restartCount remains unchanged, indicating that container's CPU resources were resized without restarting the container.

Clean up

Delete your namespace:

kubectl delete namespace qos-example

What's next

For application developers

For cluster administrators

Last modified October 30, 2024 at 5:17 PM PST: KEP 2837: Pod Level Resources Alpha (0374213f57)