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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. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:

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

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 create -f https://k8s.io/docs/tasks/administer-cluster/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.

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 create -f https://k8s.io/docs/tasks/administer-cluster/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 Container has a CPU request of 500 millicpus 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 the configuration file for a Pod that has one Container. The Container specifies a CPU limit, but not a request:

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 create -f https://k8s.io/docs/tasks/administer-cluster/cpu-defaults-pod-2.yaml --namespace=default-cpu-example

View the Pod specification:

kubectl get pod cpu-limit-no-request --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 the configuration file for a Pod that has one Container. The Container specifies a CPU request, but not a limit:

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 create -f https://k8s.io/docs/tasks/administer-cluster/cpu-defaults-pod-3.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, wh70cb02113b7c7cc1604d1951ef82e1c82850eef2ich is the default CPU limit for the namespace.

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

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.

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