Resource Quota

This example demonstrates how resource quota and limitsranger can be applied to a Kubernetes namespace. See ResourceQuota design doc for more information.

This example assumes you have a functional Kubernetes setup.

Step 1: Create a namespace

This example will work in a custom namespace to demonstrate the concepts involved.

Let's create a new namespace called quota-example:

$ kubectl create -f docs/admin/resourcequota/namespace.yaml
namespace "quota-example" created
$ kubectl get namespaces
NAME            LABELS    STATUS    AGE
default         <none>    Active    2m
quota-example   <none>    Active    39s

Step 2: Apply a quota to the namespace

By default, a pod will run with unbounded CPU and memory requests/limits. This means that any pod in the system will be able to consume as much CPU and memory on the node that executes the pod.

Users may want to restrict how much of the cluster resources a given namespace may consume across all of its pods in order to manage cluster usage. To do this, a user applies a quota to a namespace. A quota lets the user set hard limits on the total amount of node resources (cpu, memory) and API resources (pods, services, etc.) that a namespace may consume. In term of resources, Kubernetes checks the total resource requests, not resource limits of all containers/pods in the namespace.

Let's create a simple quota in our namespace:

$ kubectl create -f docs/admin/resourcequota/quota.yaml --namespace=quota-example
resourcequota "quota" created

Once your quota is applied to a namespace, the system will restrict any creation of content in the namespace until the quota usage has been calculated. This should happen quickly.

You can describe your current quota usage to see what resources are being consumed in your namespace.

$ kubectl describe quota quota --namespace=quota-example
Name:          quota
Namespace:     quota-example
Resource       Used    Hard
--------       ----    ----
cpu            0   20
memory         0   1Gi
persistentvolumeclaims 0   10
pods           0   10
replicationcontrollers 0   20
resourcequotas     1   1
secrets            1   10
services       0   5

Step 3: Applying default resource requests and limits

Pod authors rarely specify resource requests and limits for their pods.

Since we applied a quota to our project, let's see what happens when an end-user creates a pod that has unbounded cpu and memory by creating an nginx container.

To demonstrate, lets create a replication controller that runs nginx:

$ kubectl run nginx --image=nginx --replicas=1 --namespace=quota-example
replicationcontroller "nginx" created

Now let's look at the pods that were created.

$ kubectl get pods --namespace=quota-example
NAME      READY     STATUS    RESTARTS   AGE

What happened? I have no pods! Let's describe the replication controller to get a view of what is happening.

kubectl describe rc nginx --namespace=quota-example
Name:      nginx
Namespace: quota-example
Image(s):  nginx
Selector:  run=nginx
Labels:        run=nginx
Replicas:  0 current / 1 desired
Pods Status:   0 Running / 0 Waiting / 0 Succeeded / 0 Failed
No volumes.
Events:
  FirstSeen    LastSeen    Count   From                SubobjectPath   Reason      Message
  42s      11s     3   {replication-controller }           FailedCreate    Error creating: Pod "nginx-" is forbidden: Must make a non-zero request for memory since it is tracked by quota.

The Kubernetes API server is rejecting the replication controllers requests to create a pod because our pods do not specify any memory usage request.

So let's set some default values for the amount of cpu and memory a pod can consume:

$ kubectl create -f docs/admin/resourcequota/limits.yaml --namespace=quota-example
limitrange "limits" created
$ kubectl describe limits limits --namespace=quota-example
Name:      limits
Namespace: quota-example
Type       Resource    Min Max Request Limit   Limit/Request
----       --------    --- --- ------- -----   -------------
Container  memory      -   -   256Mi   512Mi   -
Container  cpu     -   -   100m    200m    -

Now any time a pod is created in this namespace, if it has not specified any resource request/limit, the default amount of cpu and memory per container will be applied, and the request will be used as part of admission control.

Now that we have applied default resource request for our namespace, our replication controller should be able to create its pods.

$ kubectl get pods --namespace=quota-example
NAME          READY     STATUS    RESTARTS   AGE
nginx-fca65   1/1       Running   0          1m

And if we print out our quota usage in the namespace:

$ kubectl describe quota quota --namespace=quota-example
Name:          quota
Namespace:     quota-example
Resource       Used    Hard
--------       ----    ----
cpu            100m    20
memory         256Mi   1Gi
persistentvolumeclaims 0   10
pods           1   10
replicationcontrollers 1   20
resourcequotas     1   1
secrets            1   10
services       0   5

You can now see the pod that was created is consuming explicit amounts of resources (specified by resource request), and the usage is being tracked by the Kubernetes system properly.

Summary

Actions that consume node resources for cpu and memory can be subject to hard quota limits defined by the namespace quota. The resource consumption is measured by resource request in pod specification.

Any action that consumes those resources can be tweaked, or can pick up namespace level defaults to meet your end goal.