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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.

A resource quota, defined by a ResourceQuota object, provides constraints that limit aggregate resource consumption per namespace. It can limit the quantity of objects that can be created in a namespace by type, as well as the total amount of compute resources that may be consumed by resources in that project.

Resource quotas work like this:

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

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 created resources.

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

You can limit the total sum of compute resources that can be requested in a given namespace.

The following resource types are supported:

Resource Name Description
cpu Across all pods in a non-terminal state, the sum of CPU requests cannot exceed this value.
limits.cpu Across all pods in a non-terminal state, the sum of CPU limits cannot exceed this value.
limits.memory Across all pods in a non-terminal state, the sum of memory limits cannot exceed this value.
memory Across all pods in a non-terminal state, the sum of memory requests cannot exceed this value.
requests.cpu Across all pods in a non-terminal state, the sum of CPU requests cannot exceed this value.
requests.memory Across all pods in a non-terminal state, the sum of memory requests cannot exceed this value.

Storage Resource Quota

You can limit the total sum of storage resources that can be requested in a given namespace.

In addition, you can limit consumption of storage resources based on associated storage-class.

Resource Name Description
requests.storage Across all persistent volume claims, the sum of storage requests cannot exceed this value.
persistentvolumeclaims The total number of persistent volume claims that can exist in the namespace.
<storage-class-name>.storageclass.storage.k8s.io/requests.storage Across all persistent volume claims associated with the storage-class-name, the sum of storage requests cannot exceed this value.
<storage-class-name>.storageclass.storage.k8s.io/persistentvolumeclaims Across all persistent volume claims associated with the storage-class-name, the total number of persistent volume claims that can exist in the namespace.

For example, if an operator wants to quota storage with gold storage class separate from bronze storage class, the operator can define a quota as follows:

Object Count Quota

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

Resource Name Description
configmaps The total number of config maps that can exist in the namespace.
persistentvolumeclaims The total number of persistent volume claims that can exist in the namespace.
pods The total number of pods in a non-terminal state that can exist in the namespace. A pod is in a terminal state if status.phase in (Failed, Succeeded) is true.
replicationcontrollers The total number of replication controllers that can exist in the namespace.
resourcequotas The total number of resource quotas that can exist in the namespace.
services The total number of services that can exist in the namespace.
services.loadbalancers The total number of services of type load balancer that can exist in the namespace.
services.nodeports The total number of services of type node port that can exist in the namespace.
secrets The total number of secrets that can exist in the namespace.

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.

Quota Scopes

Each quota can have an associated set of scopes. A quota will only measure usage for a resource if it matches the intersection of enumerated scopes.

When a scope is added to the quota, it limits the number of resources it supports to those that pertain to the scope. Resources specified on the quota outside of the allowed set results in a validation error.

Scope Description
Terminating Match pods where spec.activeDeadlineSeconds >= 0
NotTerminating Match pods where spec.activeDeadlineSeconds is nil
BestEffort Match pods that have best effort quality of service.
NotBestEffort Match pods that do not have best effort quality of service.

The BestEffort scope restricts a quota to tracking the following resource: pods

The Terminating, NotTerminating, and NotBestEffort scopes restrict a quota to tracking the following resources:

Requests vs Limits

When allocating compute resources, each container may specify a request and a limit value for either CPU or memory. The quota can be configured to quota either value.

If the quota has a value specified for requests.cpu or requests.memory, then it requires that every incoming container makes an explicit request for those resources. If the quota has a value specified for limits.cpu or limits.memory, then it requires that every incoming container specifies an explicit limit for those resources.

Viewing and Setting Quotas

Kubectl supports creating, updating, and viewing quotas:

$ kubectl create namespace myspace

$ cat <<EOF > compute-resources.yaml
apiVersion: v1
kind: ResourceQuota
metadata:
  name: compute-resources
spec:
  hard:
    pods: "4"
    requests.cpu: "1"
    requests.memory: 1Gi
    limits.cpu: "2"
    limits.memory: 2Gi
EOF
$ kubectl create -f ./compute-resources.yaml --namespace=myspace

$ cat <<EOF > object-counts.yaml
apiVersion: v1
kind: ResourceQuota
metadata:
  name: object-counts
spec:
  hard:
    configmaps: "10"
    persistentvolumeclaims: "4"
    replicationcontrollers: "20"
    secrets: "10"
    services: "10"
    services.loadbalancers: "2"
EOF
$ kubectl create -f ./object-counts.yaml --namespace=myspace

$ kubectl get quota --namespace=myspace
NAME                    AGE
compute-resources       30s
object-counts           32s

$ kubectl describe quota compute-resources --namespace=myspace
Name:                  compute-resources
Namespace:             myspace
Resource               Used Hard
--------               ---- ----
limits.cpu             0    2
limits.memory          0    2Gi
pods                   0    4
requests.cpu           0    1
requests.memory        0    1Gi

$ kubectl describe quota object-counts --namespace=myspace
Name:                   object-counts
Namespace:              myspace
Resource                Used    Hard
--------                ----    ----
configmaps              0       10
persistentvolumeclaims  0       4
replicationcontrollers  0       20
secrets                 1       10
services                0       10
services.loadbalancers  0       2

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:

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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