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| Assign CPU Resources to Containers and Pods |
{% capture overview %}
This page shows how to assign a CPU request and a CPU limit to a Container. A Container is guaranteed to have as much CPU as it requests, but is not allowed to use more CPU than its limit.
{% endcapture %}
{% capture prerequisites %}
{% include task-tutorial-prereqs.md %}
Each node in your cluster must have at least 1 CPU.
A few of the steps on this page require that the Heapster service is running in your cluster. But if you don't have Heapster running, you can do most of the steps, and it won't be a problem if you skip the Heapster steps.
To see whether the Heapster service is running, enter this command:
kubectl get services --namespace=kube-system
If the heapster service is running, it shows in the output:
NAMESPACE NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kube-system heapster 10.11.240.9 <none> 80/TCP 6d
{% endcapture %}
{% capture steps %}
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 cpu-example
Specify a CPU request and a CPU limit
To specify a CPU request for a Container, include the resources:requests field
in the Container's resource manifest. To specify a CPU limit, include resources:limits.
In this exercise, you create a Pod that has one Container. The container has a CPU request of 0.5 cpu and a CPU limit of 1 cpu. Here's the configuration file for the Pod:
{% include code.html language="yaml" file="cpu-request-limit.yaml" ghlink="/docs/tasks/configure-pod-container/cpu-request-limit.yaml" %}
In the configuration file, the args section provides arguments for the Container when it starts.
The -cpus "2" argument tells the Container to attempt to use 2 cpus.
Create the Pod:
kubectl create -f https://k8s.io/docs/tasks/configure-pod-container/cpu-request-limit.yaml --namespace=cpu-example
Verify that the Pod's Container is running:
kubectl get pod cpu-demo --namespace=cpu-example
View detailed information about the Pod:
kubectl get pod cpu-demo --output=yaml --namespace=cpu-example
The output shows that the one Container in the Pod has a CPU request of 500 millicpu and a CPU limit of 1 cpu.
resources:
limits:
cpu: "1"
requests:
cpu: 500m
Start a proxy so that you can call the heapster service:
kubectl proxy
In another command window, get the CPU usage rate from the heapster service:
curl http://localhost:8001/api/v1/proxy/namespaces/kube-system/services/heapster/api/v1/model/namespaces/cpu-example/pods/cpu-demo/metrics/cpu/usage_rate
The output shows that the Pod is using 974 millicpu, which is just a bit less than the limit of 1 cpu specified in the Pod's configuration file.
{
"timestamp": "2017-06-22T18:48:00Z",
"value": 974
}
Recall that by setting -cpu "2", you configured the Container to attempt to use 2 cpus.
But the container is only being allowed to use about 1 cpu. The Container's CPU use is being
throttled, because the Container is attempting to use more CPU resources than its limit.
Note: There's another possible explanation for the CPU throttling. The Node might not have enough CPU resources available. Recall that the prerequisites for this exercise require that each of your Nodes has at least 1 cpu. If your Container is running on a Node that has only 1 cpu, the Container cannot use more than 1 cpu regardless of the CPU limit specified for the Container.
CPU units
The CPU resource is measured in cpu units. One cpu, in Kubernetes, is equivalent to:
- 1 AWS vCPU
- 1 GCP Core
- 1 Azure vCore
- 1 Hyperthread on a bare-metal Intel processor with Hyperthreading
Fractional values are allowed. A Container that requests 0.5 cpu is guaranteed half as much CPU as a Container that requests 1 cpu. You can use the suffix m to mean milli. For example 100m cpu, 100 millicpu, and 0.1 cpu are all the same. Precision finer than 1m is not allowed.
CPU is always requested as an absolute quantity, never as a relative quantity; 0.1 is the same amount of CPU on a single-core, dual-core, or 48-core machine.
Delete your Pod:
kubectl delete pod cpu-demo --namespace=cpu-example
Specify a CPU request that is too big for your Nodes
CPU requests and limits are associated with Containers, but it is useful to think of a Pod as having a CPU request and limit. The CPU request for a Pod is the sum of the CPU requests for all the Containers in the Pod. Likewise, the CPU limit for a Pod is the sum of the CPU limits for all the Containers in the Pod.
Pod scheduling is based on requests. A Pod is scheduled to run on a Node only if the Node has enough CPU resources available to satisfy the Pod’s CPU request.
In this exercise, you create a Pod that has a CPU request so big that it exceeds the capacity of any Node in your cluster. Here is the configuration file for a Pod that has one Container. The Container requests 100 cpu, which is likely to exceed the capacity of any Node in your cluster.
{% include code.html language="yaml" file="cpu-request-limit-2.yaml" ghlink="/docs/tasks/configure-pod-container/cpu-request-limit-2.yaml" %}
Create the Pod:
kubectl create -f https://k8s.io/docs/tasks/configure-pod-container/cpu-request-limit-2.yaml --namespace=cpu-example
View the Pod's status:
kubectl get pod cpu-demo-2 --namespace=cpu-example
The output shows that the Pod's status is Pending. That is, the Pod has not been scheduled to run on any Node, and it will remain in the Pending state indefinitely:
kubectl get pod cpu-demo-2 --namespace=cpu-example
NAME READY STATUS RESTARTS AGE
cpu-demo-2 0/1 Pending 0 7m
View detailed information about the Pod, including events:
kubectl describe pod cpu-demo-2 --namespace=cpu-example
The output shows that the Container cannot be scheduled because of insufficient CPU resources on the Nodes:
Events:
Reason Message
------ -------
FailedScheduling No nodes are available that match all of the following predicates:: Insufficient cpu (3).
Delete your Pod:
kubectl delete pod cpu-demo-2 --namespace=cpu-example
If you don’t specify a CPU limit
If you don’t specify a CPU limit for a Container, then one of these situations applies:
-
The Container has no upper bound on the CPU resources it can use. The Container could use all of the CPU resources available on the Node where it is running.
-
The Container is running in a namespace that has a default CPU limit, and the Container is automatically assigned the default limit. Cluster administrators can use a LimitRange to specify a default value for the CPU limit.
Motivation for CPU requests and limits
By configuring the CPU requests and limits of the Containers that run in your cluster, you can make efficient use of the CPU resources available on your cluster's Nodes. By keeping a Pod's CPU request low, you give the Pod a good chance of being scheduled. By having a CPU limit that is greater than the CPU request, you accomplish two things:
- The Pod can have bursts of activity where it makes use of CPU resources that happen to be available.
- The amount of CPU resources a Pod can use during a burst is limited to some reasonable amount.
Clean up
Delete your namespace:
kubectl delete namespace cpu-example
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{% capture whatsnext %}
For app developers
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
{% endcapture %}
{% include templates/task.md %}