This page shows how to set minimum and maximum values for the CPU resources used by Containers and Pods in a namespace. You specify minimum and maximum CPU values in a LimitRange object. If a Pod does not meet the constraints imposed by the LimitRange, it cannot be created in the namespace.
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:
To check the version, enter kubectl version
.
Each node in your cluster must have at least 1 CPU.
Create a namespace so that the resources you create in this exercise are isolated from the rest of your cluster.
kubectl create namespace constraints-cpu-example
Here’s the configuration file for a LimitRange:
admin/resource/cpu-constraints.yaml
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Create the LimitRange:
kubectl create -f https://k8s.io/examples/admin/resource/cpu-constraints.yaml --namespace=constraints-cpu-example
View detailed information about the LimitRange:
kubectl get limitrange cpu-min-max-demo-lr --output=yaml --namespace=constraints-cpu-example
The output shows the minimum and maximum CPU constraints as expected. But notice that even though you didn’t specify default values in the configuration file for the LimitRange, they were created automatically.
limits:
- default:
cpu: 800m
defaultRequest:
cpu: 800m
max:
cpu: 800m
min:
cpu: 200m
type: Container
Now whenever a Container is created in the constraints-cpu-example namespace, Kubernetes performs these steps:
If the Container does not specify its own CPU request and limit, assign the default CPU request and limit to the Container.
Verify that the Container specifies a CPU request that is greater than or equal to 200 millicpu.
Verify that the Container specifies a CPU limit that is less than or equal to 800 millicpu.
Note: When creating aLimitRange
object, you can specify limits on huge-pages or GPUs as well. However, when bothdefault
anddefaultRequest
are specified on these resources, the two values must be the same.
Here’s the configuration file for a Pod that has one Container. The Container manifest specifies a CPU request of 500 millicpu and a CPU limit of 800 millicpu. These satisfy the minimum and maximum CPU constraints imposed by the LimitRange.
admin/resource/cpu-constraints-pod.yaml
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Create the Pod:
kubectl create -f https://k8s.io/examples/admin/resource/cpu-constraints-pod.yaml --namespace=constraints-cpu-example
Verify that the Pod’s Container is running:
kubectl get pod constraints-cpu-demo --namespace=constraints-cpu-example
View detailed information about the Pod:
kubectl get pod constraints-cpu-demo --output=yaml --namespace=constraints-cpu-example
The output shows that the Container has a CPU request of 500 millicpu and CPU limit of 800 millicpu. These satisfy the constraints imposed by the LimitRange.
resources:
limits:
cpu: 800m
requests:
cpu: 500m
kubectl delete pod constraints-cpu-demo --namespace=constraints-cpu-example
Here’s the configuration file for a Pod that has one Container. The Container specifies a CPU request of 500 millicpu and a cpu limit of 1.5 cpu.
admin/resource/cpu-constraints-pod-2.yaml
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Attempt to create the Pod:
kubectl create -f https://k8s.io/examples/admin/resource/cpu-constraints-pod-2.yaml --namespace=constraints-cpu-example
The output shows that the Pod does not get created, because the Container specifies a CPU limit that is too large:
Error from server (Forbidden): error when creating "examples/admin/resource/cpu-constraints-pod-2.yaml":
pods "constraints-cpu-demo-2" is forbidden: maximum cpu usage per Container is 800m, but limit is 1500m.
Here’s the configuration file for a Pod that has one Container. The Container specifies a CPU request of 100 millicpu and a CPU limit of 800 millicpu.
admin/resource/cpu-constraints-pod-3.yaml
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Attempt to create the Pod:
kubectl create -f https://k8s.io/examples/admin/resource/cpu-constraints-pod-3.yaml --namespace=constraints-cpu-example
The output shows that the Pod does not get created, because the Container specifies a CPU request that is too small:
Error from server (Forbidden): error when creating "examples/admin/resource/cpu-constraints-pod-3.yaml":
pods "constraints-cpu-demo-4" is forbidden: minimum cpu usage per Container is 200m, but request is 100m.
Here’s the configuration file for a Pod that has one Container. The Container does not specify a CPU request, and it does not specify a CPU limit.
admin/resource/cpu-constraints-pod-4.yaml
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Create the Pod:
kubectl create -f https://k8s.io/examples/admin/resource/cpu-constraints-pod-4.yaml --namespace=constraints-cpu-example
View detailed information about the Pod:
kubectl get pod constraints-cpu-demo-4 --namespace=constraints-cpu-example --output=yaml
The output shows that the Pod’s Container has a CPU request of 800 millicpu and a CPU limit of 800 millicpu. How did the Container get those values?
resources:
limits:
cpu: 800m
requests:
cpu: 800m
Because your Container did not specify its own CPU request and limit, it was given the default CPU request and limit from the LimitRange.
At this point, your Container might be running or it might not be running. Recall that a prerequisite for this task is that your Nodes have at least 1 CPU. If each of your Nodes has only 1 CPU, then there might not be enough allocatable CPU on any Node to accommodate a request of 800 millicpu. If you happen to be using Nodes with 2 CPU, then you probably have enough CPU to accommodate the 800 millicpu request.
Delete your Pod:
kubectl delete pod constraints-cpu-demo-4 --namespace=constraints-cpu-example
The maximum and minimum CPU constraints imposed on a namespace by a LimitRange are enforced only when a Pod is created or updated. If you change the LimitRange, it does not affect Pods that were created previously.
As a cluster administrator, you might want to impose restrictions on the CPU resources that Pods can use. For example:
Each Node in a cluster has 2 CPU. You do not want to accept any Pod that requests more than 2 CPU, because no Node in the cluster can support the request.
A cluster is shared by your production and development departments. You want to allow production workloads to consume up to 3 CPU, but you want development workloads to be limited to 1 CPU. You create separate namespaces for production and development, and you apply CPU constraints to each namespace.
Delete your namespace:
kubectl delete namespace constraints-cpu-example
Configure Default Memory Requests and Limits for a Namespace
Configure Minimum and Maximum Memory Constraints for a Namespace
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