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WARNING WARNING WARNING WARNING WARNING

PLEASE NOTE: This document applies to the HEAD of the source tree

If you are using a released version of Kubernetes, you should refer to the docs that go with that version.

The latest 1.0.x release of this document can be found [here](http://releases.k8s.io/release-1.0/docs/admin/resource-quota.md).

Documentation for other releases can be found at releases.k8s.io.

Resource Quotas

When several users or teams share a cluster with a fixed number of nodes, there is a concern that one team could use more than its fair share of resources.

Resource quotas are a tool for administrators to address this concern. Resource quotas work like this:

  • Different teams work in different namespaces. Currently this is voluntary, but support for making this mandatory via ACLs is planned.
  • Users put compute resource limits on their pods.
  • The administrator creates a Resource Quota for each namespace.
  • If creating a pod would cause the namespace to exceed any of the limits specified in the the Resource Quota for that namespace, then the request will fail with HTTP status code 403 FORBIDDEN.
  • If quota is enabled in a namespace and the user does not specify limits on the pod for each of the resources for which quota is enabled, then the POST of the pod will fail with HTTP status code 403 FORBIDDEN. Hint: Use the LimitRange admission controller to force default values of limits before the quota is checked to avoid this problem.

Examples of policies that could be created using namespaces and quotas are:

  • In a cluster with a capacity of 32 GiB RAM, and 16 cores, let team A use 20 Gib and 10 cores, let B use 10GiB and 4 cores, and hold 2GiB and 2 cores in reserve for future allocation.
  • Limit the "testing" namespace to using 1 core and 1GiB RAM. Let the "production" namespace use any amount.

In the case where the total capacity of the cluster is less than the sum of the quotas of the namespaces, there may be contention for resources. This is handled on a first-come-first-served basis.

Neither contention nor changes to quota will affect already-running pods.

Enabling Resource Quota

Resource Quota support is enabled by default for many Kubernetes distributions. It is enabled when the apiserver --admission_control= flag has ResourceQuota as one of its arguments.

Resource Quota is enforced in a particular namespace when there is a ResourceQuota object in that namespace. There should be at most one ResourceQuota object in a namespace.

Compute Resource Quota

The total sum of compute resources requested by pods in a namespace can be limited. The following compute resource types are supported:

ResourceName Description
cpu Total cpu limits of containers
memory Total memory limits of containers

For example, cpu quota sums up the resources.limits.cpu fields of every container of every pod in the namespace, and enforces a maximum on that sum.

Object Count Quota

The number of objects of a given type can be restricted. The following types are supported:

ResourceName Description
pods Total number of pods
services Total number of services
replicationcontrollers Total number of replication controllers
resourcequotas Total number of resource quotas
secrets Total number of secrets
persistentvolumeclaims Total number of persistent volume claims

For example, pods quota counts and enforces a maximum on the number of pods created in a single namespace.

You might want to set a pods quota on a namespace to avoid the case where a user creates many small pods and exhausts the cluster's supply of Pod IPs.

Viewing and Setting Quotas

Kubectl supports creating, updating, and viewing quotas

$ kubectl namespace myspace
$ cat <<EOF > quota.json
{
  "apiVersion": "v1",
  "kind": "ResourceQuota",
  "metadata": {
    "name": "quota",
  },
  "spec": {
    "hard": {
      "memory": "1Gi",
      "cpu": "20",
      "pods": "10",
      "services": "5",
      "replicationcontrollers":"20",
      "resourcequotas":"1",
    },
  }
}
EOF
$ kubectl create -f ./quota.json
$ kubectl get quota
NAME
quota
$ kubectl describe quota quota
Name:                   quota
Resource                Used    Hard
--------                ----    ----
cpu                     0m      20
memory                  0       1Gi
pods                    5       10
replicationcontrollers  5       20
resourcequotas          1       1
services                3       5

Quota and Cluster Capacity

Resource Quota objects are independent of the Cluster Capacity. They are expressed in absolute units. So, if you add nodes to your cluster, this does not automatically give each namespace the ability to consume more resources.

Sometimes more complex policies may be desired, such as:

  • proportionally divide total cluster resources among several teams.
  • allow each tenant to grow resource usage as needed, but have a generous limit to prevent accidental resource exhaustion.
  • detect demand from one namespace, add nodes, and increase quota.

Such policies could be implemented using ResourceQuota as a building-block, by writing a 'controller' which watches the quota usage and adjusts the quota hard limits of each namespace according to other signals.

Note that resource quota divides up aggregate cluster resources, but it creates no restrictions around nodes: pods from several namespaces may run on the same node.

Example

See a detailed example for how to use resource quota.

Read More

See ResourceQuota design doc for more information.

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