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 namespace.

Resource quotas work like this:

• Different teams work in different namespaces. This can be enforced with RBAC.

• The administrator creates one ResourceQuota for each namespace.

• Users create resources (pods, services, etc.) in the namespace, and the quota system tracks usage to ensure it does not exceed hard resource limits defined in a ResourceQuota.

• If creating or updating a resource violates a quota constraint, the request will fail with HTTP status code 403 FORBIDDEN with a message explaining the constraint that would have been violated.

• If quota is enabled in a namespace for compute resources like cpu and memory, users must specify requests or limits for those values; otherwise, the quota system may reject pod creation. Hint: Use the LimitRanger admission controller to force defaults for pods that make no compute resource requirements.

  See the walkthrough for an example of how to avoid this problem.

The name of a ResourceQuota object must be a valid DNS subdomain name.

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 created resources.

Enabling Resource Quota

ResourceQuota support is enabled by default for many Kubernetes distributions. It is enabled when the API server --enable-admission-plugins= flag has ResourceQuota as one of its arguments.

A resource quota is enforced in a particular namespace when there is a ResourceQuota in that 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 Quota For Extended Resources

In addition to the resources mentioned above, in release 1.10, quota support for extended resources is added.

As overcommit is not allowed for extended resources, it makes no sense to specify both requests and limits for the same extended resource in a quota. So for extended resources, only quota items with prefix requests. are allowed.

Take the GPU resource as an example, if the resource name is nvidia.com/gpu, and you want to limit the total number of GPUs requested in a namespace to 4, you can define a quota as follows:

• requests.nvidia.com/gpu: 4

See Viewing and Setting Quotas for more details.

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.

For example, if you want to quota storage with gold StorageClass separate from a bronze StorageClass, you can define a quota as follows:

• gold.storageclass.storage.k8s.io/requests.storage: 500Gi
• bronze.storageclass.storage.k8s.io/requests.storage: 100Gi

In release 1.8, quota support for local ephemeral storage is added as an alpha feature:

Object Count Quota

You can set quota for the total number of one particular resource kind in the Kubernetes API, using the following syntax:

• count/<resource>.<group> for resources from non-core groups
• count/<resource> for resources from the core group

Here is an example set of resources users may want to put under object count quota:

• count/persistentvolumeclaims
• count/services
• count/secrets
• count/configmaps
• count/replicationcontrollers
• count/deployments.apps
• count/replicasets.apps
• count/statefulsets.apps
• count/jobs.batch
• count/cronjobs.batch

If you define a quota this way, it applies to Kubernetes' APIs that are part of the API server, and to any custom resources backed by a CustomResourceDefinition. If you use API aggregation to add additional, custom APIs that are not defined as CustomResourceDefinitions, the core Kubernetes control plane does not enforce quota for the aggregated API. The extension API server is expected to provide quota enforcement if that's appropriate for the custom API. For example, to create a quota on a widgets custom resource in the example.com API group, use count/widgets.example.com.

When using such a resource quota (nearly for all object kinds), an object is charged against the quota if the object kind exists (is defined) in the control plane. These types of quotas are useful to protect against exhaustion of storage resources. For example, you may want to limit the number of Secrets in a server given their large size. Too many Secrets in a cluster can actually prevent servers and controllers from starting. You can set a quota for Jobs to protect against a poorly configured CronJob. CronJobs that create too many Jobs in a namespace can lead to a denial of service.

There is another syntax only to set the same type of quota for certain resources. The following types are supported:

For example, pods quota counts and enforces a maximum on the number of pods created in a single namespace that are not terminal. 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.

You can find more examples on Viewing and Setting Quotas.

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.

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

• pods

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

• pods
• cpu
• memory
• requests.cpu
• requests.memory
• limits.cpu
• limits.memory

Note that you cannot specify both the Terminating and the NotTerminating scopes in the same quota, and you cannot specify both the BestEffort and NotBestEffort scopes in the same quota either.

The scopeSelector supports the following values in the operator field:

• In
• NotIn
• Exists
• DoesNotExist

When using one of the following values as the scopeName when defining the scopeSelector, the operator must be Exists.

• Terminating
• NotTerminating
• BestEffort
• NotBestEffort

If the operator is In or NotIn, the values field must have at least one value. For example:

  scopeSelector:
    matchExpressions:
      - scopeName: PriorityClass
        operator: In
        values:
          - middle

If the operator is Exists or DoesNotExist, the values field must NOT be specified.

Resource Quota Per PriorityClass

Pods can be created at a specific priority. You can control a pod's consumption of system resources based on a pod's priority, by using the scopeSelector field in the quota spec.

A quota is matched and consumed only if scopeSelector in the quota spec selects the pod.

When quota is scoped for priority class using scopeSelector field, quota object is restricted to track only following resources:

• pods
• cpu
• memory
• ephemeral-storage
• limits.cpu
• limits.memory
• limits.ephemeral-storage
• requests.cpu
• requests.memory
• requests.ephemeral-storage

This example creates a quota object and matches it with pods at specific priorities. The example works as follows:

• Pods in the cluster have one of the three priority classes, "low", "medium", "high".
• One quota object is created for each priority.

Save the following YAML to a file quota.yml.

apiVersion: v1
kind: List
items:
- apiVersion: v1
  kind: ResourceQuota
  metadata:
    name: pods-high
  spec:
    hard:
      cpu: "1000"
      memory: 200Gi
      pods: "10"
    scopeSelector:
      matchExpressions:
      - operator : In
        scopeName: PriorityClass
        values: ["high"]
- apiVersion: v1
  kind: ResourceQuota
  metadata:
    name: pods-medium
  spec:
    hard:
      cpu: "10"
      memory: 20Gi
      pods: "10"
    scopeSelector:
      matchExpressions:
      - operator : In
        scopeName: PriorityClass
        values: ["medium"]
- apiVersion: v1
  kind: ResourceQuota
  metadata:
    name: pods-low
  spec:
    hard:
      cpu: "5"
      memory: 10Gi
      pods: "10"
    scopeSelector:
      matchExpressions:
      - operator : In
        scopeName: PriorityClass
        values: ["low"]

Apply the YAML using kubectl create.

kubectl create -f ./quota.yml

resourcequota/pods-high created
resourcequota/pods-medium created
resourcequota/pods-low created

Verify that Used quota is 0 using kubectl describe quota.

kubectl describe quota

Name:       pods-high
Namespace:  default
Resource    Used  Hard
--------    ----  ----
cpu         0     1k
memory      0     200Gi
pods        0     10


Name:       pods-low
Namespace:  default
Resource    Used  Hard
--------    ----  ----
cpu         0     5
memory      0     10Gi
pods        0     10


Name:       pods-medium
Namespace:  default
Resource    Used  Hard
--------    ----  ----
cpu         0     10
memory      0     20Gi
pods        0     10

Create a pod with priority "high". Save the following YAML to a file high-priority-pod.yml.

apiVersion: v1
kind: Pod
metadata:
  name: high-priority
spec:
  containers:
  - name: high-priority
    image: ubuntu
    command: ["/bin/sh"]
    args: ["-c", "while true; do echo hello; sleep 10;done"]
    resources:
      requests:
        memory: "10Gi"
        cpu: "500m"
      limits:
        memory: "10Gi"
        cpu: "500m"
  priorityClassName: high

Apply it with kubectl create.

kubectl create -f ./high-priority-pod.yml

Verify that "Used" stats for "high" priority quota, pods-high, has changed and that the other two quotas are unchanged.

kubectl describe quota

Name:       pods-high
Namespace:  default
Resource    Used  Hard
--------    ----  ----
cpu         500m  1k
memory      10Gi  200Gi
pods        1     10


Name:       pods-low
Namespace:  default
Resource    Used  Hard
--------    ----  ----
cpu         0     5
memory      0     10Gi
pods        0     10


Name:       pods-medium
Namespace:  default
Resource    Used  Hard
--------    ----  ----
cpu         0     10
memory      0     20Gi
pods        0     10

Cross-namespace Pod Affinity Quota

Operators can use CrossNamespacePodAffinity quota scope to limit which namespaces are allowed to have pods with affinity terms that cross namespaces. Specifically, it controls which pods are allowed to set namespaces or namespaceSelector fields in pod affinity terms.

Preventing users from using cross-namespace affinity terms might be desired since a pod with anti-affinity constraints can block pods from all other namespaces from getting scheduled in a failure domain.

Using this scope operators can prevent certain namespaces (foo-ns in the example below) from having pods that use cross-namespace pod affinity by creating a resource quota object in that namespace with CrossNamespacePodAffinity scope and hard limit of 0:

apiVersion: v1
kind: ResourceQuota
metadata:
  name: disable-cross-namespace-affinity
  namespace: foo-ns
spec:
  hard:
    pods: "0"
  scopeSelector:
    matchExpressions:
    - scopeName: CrossNamespacePodAffinity
      operator: Exists

If operators want to disallow using namespaces and namespaceSelector by default, and only allow it for specific namespaces, they could configure CrossNamespacePodAffinity as a limited resource by setting the kube-apiserver flag --admission-control-config-file to the path of the following configuration file:

apiVersion: apiserver.config.k8s.io/v1
kind: AdmissionConfiguration
plugins:
- name: "ResourceQuota"
  configuration:
    apiVersion: apiserver.config.k8s.io/v1
    kind: ResourceQuotaConfiguration
    limitedResources:
    - resource: pods
      matchScopes:
      - scopeName: CrossNamespacePodAffinity
        operator: Exists

With the above configuration, pods can use namespaces and namespaceSelector in pod affinity only if the namespace where they are created have a resource quota object with CrossNamespacePodAffinity scope and a hard limit greater than or equal to the number of pods using those fields.

Requests compared to 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:
    requests.cpu: "1"
    requests.memory: 1Gi
    limits.cpu: "2"
    limits.memory: 2Gi
    requests.nvidia.com/gpu: 4
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"
    pods: "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
requests.cpu             0     1
requests.memory          0     1Gi
requests.nvidia.com/gpu  0     4

kubectl describe quota object-counts --namespace=myspace

Name:                   object-counts
Namespace:              myspace
Resource                Used    Hard
--------                ----    ----
configmaps              0       10
persistentvolumeclaims  0       4
pods                    0       4
replicationcontrollers  0       20
secrets                 1       10
services                0       10
services.loadbalancers  0       2

kubectl also supports object count quota for all standard namespaced resources using the syntax count/<resource>.<group>:

kubectl create namespace myspace

kubectl create quota test --hard=count/deployments.apps=2,count/replicasets.apps=4,count/pods=3,count/secrets=4 --namespace=myspace

kubectl create deployment nginx --image=nginx --namespace=myspace --replicas=2

kubectl describe quota --namespace=myspace

Name:                         test
Namespace:                    myspace
Resource                      Used  Hard
--------                      ----  ----
count/deployments.apps        1     2
count/pods                    2     3
count/replicasets.apps        1     4
count/secrets                 1     4

Quota and Cluster Capacity

ResourceQuotas 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 ResourceQuotas as building blocks, by writing a "controller" that 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.

Limit Priority Class consumption by default

It may be desired that pods at a particular priority, such as "cluster-services", should be allowed in a namespace, if and only if, a matching quota object exists.

With this mechanism, operators are able to restrict usage of certain high priority classes to a limited number of namespaces and not every namespace will be able to consume these priority classes by default.

To enforce this, kube-apiserver flag --admission-control-config-file should be used to pass path to the following configuration file:

apiVersion: apiserver.config.k8s.io/v1
kind: AdmissionConfiguration
plugins:
- name: "ResourceQuota"
  configuration:
    apiVersion: apiserver.config.k8s.io/v1
    kind: ResourceQuotaConfiguration
    limitedResources:
    - resource: pods
      matchScopes:
      - scopeName: PriorityClass
        operator: In
        values: ["cluster-services"]

Then, create a resource quota object in the kube-system namespace:

policy/priority-class-resourcequota.yaml

apiVersion: v1
kind: ResourceQuota
metadata:
  name: pods-cluster-services
spec:
  scopeSelector:
    matchExpressions:
      - operator : In
        scopeName: PriorityClass
        values: ["cluster-services"]

kubectl apply -f https://k8s.io/examples/policy/priority-class-resourcequota.yaml -n kube-system

resourcequota/pods-cluster-services created

In this case, a pod creation will be allowed if:

1. the Pod's priorityClassName is not specified.
2. the Pod's priorityClassName is specified to a value other than cluster-services.
3. the Pod's priorityClassName is set to cluster-services, it is to be created in the kube-system namespace, and it has passed the resource quota check.

A Pod creation request is rejected if its priorityClassName is set to cluster-services and it is to be created in a namespace other than kube-system.

What's next

• See ResourceQuota design document for more information.
• See a detailed example for how to use resource quota.
• Read Quota support for priority class design document.
• See LimitedResources.