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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:

• Different teams work in different namespaces. Currently this is voluntary, but support for making this mandatory via ACLs is planned.
• The administrator creates one or more Resource Quota objects 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 Resource Quota.
• 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 LimitRange admission controller to force defaults for pods that make no compute resource requirements. See the walkthrough for an example 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 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

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

Object Count Quota

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

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.

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:

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

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 explict 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:

• 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.