Configure Default CPU Requests and Limits for a Namespace

Define a default CPU resource limits for a namespace, so that every new Pod in that namespace has a CPU resource limit configured.

This page shows how to configure default CPU requests and limits for a namespace.

A Kubernetes cluster can be divided into namespaces. If you create a Pod within a namespace that has a default CPUlimit, and any container in that Pod does not specify its own CPU limit, then the control plane assigns the default CPU limit to that container.

Kubernetes assigns a default CPUrequest,but only under certain conditions that are explained later in this page.

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 usingminikube or you can use one of these Kubernetes playgrounds:

You must have access to create namespaces in your cluster.

If you're not already familiar with what Kubernetes means by 1.0 CPU,read meaning of CPU.

Create a namespace

Create a namespace so that the resources you create in this exercise are isolated from the rest of your cluster.

kubectl create namespace default-cpu-example

Create a LimitRange and a Pod

Here's a manifest for an example LimitRange.The manifest specifies a default CPU request and a default CPU limit.

admin/resource/cpu-defaults.yaml 
apiVersion: v1
kind: LimitRange
metadata:
  name: cpu-limit-range
spec:
  limits:
  - default:
      cpu: 1
    defaultRequest:
      cpu: 0.5
    type: Container

Create the LimitRange in the default-cpu-example namespace:

kubectl apply -f https://k8s.io/examples/admin/resource/cpu-defaults.yaml --namespace=default-cpu-example

Now if you create a Pod in the default-cpu-example namespace, and any container in that Pod does not specify its own values for CPU request and CPU limit,then the control plane applies default values: a CPU request of 0.5 and a default CPU limit of 1.

Here's a manifest for a Pod that has one container. The container does not specify a CPU request and limit.

admin/resource/cpu-defaults-pod.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: default-cpu-demo
spec:
  containers:
  - name: default-cpu-demo-ctr
    image: nginx

Create the Pod.

kubectl apply -f https://k8s.io/examples/admin/resource/cpu-defaults-pod.yaml --namespace=default-cpu-example

View the Pod's specification:

kubectl get pod default-cpu-demo --output=yaml --namespace=default-cpu-example

The output shows that the Pod's only container has a CPU request of 500m cpu (which you can read as “500 millicpu”), and a CPU limit of 1 cpu.These are the default values specified by the LimitRange.

containers:
- image: nginx
  imagePullPolicy: Always
  name: default-cpu-demo-ctr
  resources:
    limits:
      cpu: "1"
    requests:
      cpu: 500m

What if you specify a container's limit, but not its request?

Here's a manifest for a Pod that has one container. The container specifies a CPU limit, but not a request:

admin/resource/cpu-defaults-pod-2.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: default-cpu-demo-2
spec:
  containers:
  - name: default-cpu-demo-2-ctr
    image: nginx
    resources:
      limits:
        cpu: "1"

Create the Pod:

kubectl apply -f https://k8s.io/examples/admin/resource/cpu-defaults-pod-2.yaml --namespace=default-cpu-example

View the specification of the Pod that you created:

kubectl get pod default-cpu-demo-2 --output=yaml --namespace=default-cpu-example

The output shows that the container's CPU request is set to match its CPU limit.Notice that the container was not assigned the default CPU request value of 0.5 cpu:

resources:
  limits:
    cpu: "1"
  requests:
    cpu: "1"

What if you specify a container's request, but not its limit?

Here's an example manifest for a Pod that has one container. The container specifies a CPU request, but not a limit:

admin/resource/cpu-defaults-pod-3.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: default-cpu-demo-3
spec:
  containers:
  - name: default-cpu-demo-3-ctr
    image: nginx
    resources:
      requests:
        cpu: "0.75"

Create the Pod:

kubectl apply -f https://k8s.io/examples/admin/resource/cpu-defaults-pod-3.yaml --namespace=default-cpu-example

View the specification of the Pod that you created:

kubectl get pod default-cpu-demo-3 --output=yaml --namespace=default-cpu-example

The output shows that the container's CPU request is set to the value you specified at the time you created the Pod (in other words: it matches the manifest).However, the same container's CPU limit is set to 1 cpu, which is the default CPU limit for that namespace.

resources:
  limits:
    cpu: "1"
  requests:
    cpu: 750m

Motivation for default CPU limits and requests

If your namespace has a CPU resource quota configured,it is helpful to have a default value in place for CPU limit.Here are two of the restrictions that a CPU resource quota imposes on a namespace:

  • For every Pod that runs in the namespace, each of its containers must have a CPU limit.
  • CPU limits apply a resource reservation on the node where the Pod in question is scheduled.The total amount of CPU that is reserved for use by all Pods in the namespace must not exceed a specified limit.

When you add a LimitRange:

If any Pod in that namespace that includes a container does not specify its own CPU limit,the control plane applies the default CPU limit to that container, and the Pod can be allowed to run in a namespace that is restricted by a CPU ResourceQuota.

Clean up

Delete your namespace:

kubectl delete namespace default-cpu-example

What's next

For cluster administrators

For app developers


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