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 you create a Pod within a namespace that has a default CPU limit, 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 CPU request, 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 using minikube 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.
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.
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:
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:
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
-
Configure Default Memory Requests and Limits for a Namespace
-
Configure Minimum and Maximum Memory Constraints for a Namespace
-
Configure Minimum and Maximum CPU Constraints for a Namespace