Configure Default CPU Requests and Limits for a Namespace

This page shows how to configure default CPU requests and limits for a namespace. A Kubernetes cluster can be divided into namespaces. If a Container is created in a namespace that has a default CPU limit, and the Container does not specify its own CPU limit, then the Container is assigned the default CPU limit. Kubernetes assigns a default CPU request under certain conditions that are explained later in this topic.

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:

To check the version, enter kubectl version.

Create a namespace

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

  1. kubectl create namespace default-cpu-example

Create a LimitRange and a Pod

Here’s the configuration file for a LimitRange object. The configuration specifies a default CPU request and a default CPU limit.

admin/resource/cpu-defaults.yaml Configure Default CPU Requests and Limits for a Namespace - 图1

  1. apiVersion: v1
  2. kind: LimitRange
  3. metadata:
  4.   name: cpu-limit-range
  5. spec:
  6.   limits:
  7.   - default:
  8.       cpu: 1
  9.     defaultRequest:
  10.       cpu: 0.5
  11.     type: Container

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

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

Now if a Container is created in the default-cpu-example namespace, and the Container does not specify its own values for CPU request and CPU limit, the Container is given a default CPU request of 0.5 and a default CPU limit of 1.

Here’s the configuration file for a Pod that has one Container. The Container does not specify a CPU request and limit.

admin/resource/cpu-defaults-pod.yaml Configure Default CPU Requests and Limits for a Namespace - 图2

  1. apiVersion: v1
  2. kind: Pod
  3. metadata:
  4.   name: default-cpu-demo
  5. spec:
  6.   containers:
  7.   - name: default-cpu-demo-ctr
  8.     image: nginx

Create the Pod.

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

View the Pod’s specification:

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

The output shows that the Pod’s Container has a CPU request of 500 millicpus and a CPU limit of 1 cpu. These are the default values specified by the LimitRange.

  1. containers:
  2. - image: nginx
  3.   imagePullPolicy: Always
  4.   name: default-cpu-demo-ctr
  5.   resources:
  6.     limits:
  7.       cpu: "1"
  8.     requests:
  9.       cpu: 500m

What if you specify a Container’s limit, but not its request?

Here’s the configuration file for a Pod that has one Container. The Container specifies a CPU limit, but not a request:

admin/resource/cpu-defaults-pod-2.yaml Configure Default CPU Requests and Limits for a Namespace - 图3

  1. apiVersion: v1
  2. kind: Pod
  3. metadata:
  4.   name: default-cpu-demo-2
  5. spec:
  6.   containers:
  7.   - name: default-cpu-demo-2-ctr
  8.     image: nginx
  9.     resources:
  10.       limits:
  11.         cpu: "1"

Create the Pod:

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

View the Pod specification:

  1. 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.

  1. resources:
  2.   limits:
  3.     cpu: "1"
  4.   requests:
  5.     cpu: "1"

What if you specify a Container’s request, but not its limit?

Here’s the configuration file for a Pod that has one Container. The Container specifies a CPU request, but not a limit:

admin/resource/cpu-defaults-pod-3.yaml Configure Default CPU Requests and Limits for a Namespace - 图4

  1. apiVersion: v1
  2. kind: Pod
  3. metadata:
  4.   name: default-cpu-demo-3
  5. spec:
  6.   containers:
  7.   - name: default-cpu-demo-3-ctr
  8.     image: nginx
  9.     resources:
  10.       requests:
  11.         cpu: "0.75"

Create the Pod:

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

View the Pod specification:

  1. 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 specified in the Container’s configuration file. The Container’s CPU limit is set to 1 cpu, which is the default CPU limit for the namespace.

  1. resources:
  2.   limits:
  3.     cpu: "1"
  4.   requests:
  5.     cpu: 750m

Motivation for default CPU limits and requests

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

  • Every Container that runs in the namespace must have its own CPU limit.
  • The total amount of CPU used by all Containers in the namespace must not exceed a specified limit.

If a Container does not specify its own CPU limit, it is given the default limit, and then it can be allowed to run in a namespace that is restricted by a quota.

Clean up

Delete your namespace:

  1. kubectl delete namespace default-cpu-example

What’s next

For cluster administrators

For app developers