Overview

Using quotas and limit ranges, cluster administrators can set constraints to limit the number of objects or amount of compute resources that are used in your project. This helps cluster administrators better manage and allocate resources across all projects, and ensure that no projects are using more than is appropriate for the cluster size.

As a developer, you can also set requests and limits on compute resources at the pod and container level.

The following sections help you understand how to check on your quota and limit range settings, what sorts of things they can constrain, and how you can request or limit compute resources in your own pods and containers.

Quotas

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

Quotas are set by cluster administrators and are scoped to a given project.

Viewing Quotas

You can view usage statistics related to any hard limits defined in a project’s quota by navigating in the web console to the project’s Settings tab.

You can also use the CLI to view quota details:

  1. First, get the list of quotas defined in the project. For example, for a project called demoproject:

    $ oc get quota -n demoproject
    NAME                AGE
    besteffort          11m
    compute-resources   2m
    core-object-counts  29m
  2. Then, describe the quota you are interested in, for example the core-object-counts quota:

    $ oc describe quota core-object-counts -n demoproject
    Name:			core-object-counts
    Namespace:		demoproject
    Resource		Used	Hard
    --------		----	----
    configmaps		3	10
    persistentvolumeclaims	0	4
    replicationcontrollers	3	20
    secrets			9	10
    services		2	10

Full quota definitions can be viewed by running oc export on the object. The following show some sample quota definitions:

Example 1. core-object-counts.yaml
apiVersion: v1
kind: ResourceQuota
metadata:
  name: core-object-counts
spec:
  hard:
    configmaps: "10" (1)
    persistentvolumeclaims: "4" (2)
    replicationcontrollers: "20" (3)
    secrets: "10" (4)
    services: "10" (5)
1 The total number of ConfigMap objects that can exist in the project.
2 The total number of persistent volume claims (PVCs) that can exist in the project.
3 The total number of replication controllers that can exist in the project.
4 The total number of secrets that can exist in the project.
5 The total number of services that can exist in the project.
Example 2. openshift-object-counts.yaml
apiVersion: v1
kind: ResourceQuota
metadata:
  name: openshift-object-counts
spec:
  hard:
    openshift.io/imagestreams: "10" (1)
1 The total number of image streams that can exist in the project.
Example 3. compute-resources.yaml
apiVersion: v1
kind: ResourceQuota
metadata:
  name: compute-resources
spec:
  hard:
    pods: "4" (1)
    requests.cpu: "1" (2)
    requests.memory: 1Gi (3)
    limits.cpu: "2" (4)
    limits.memory: 2Gi (5)
1 The total number of pods in a non-terminal state that can exist in the project.
2 Across all pods in a non-terminal state, the sum of CPU requests cannot exceed 1 core.
3 Across all pods in a non-terminal state, the sum of memory requests cannot exceed 1Gi.
4 Across all pods in a non-terminal state, the sum of CPU limits cannot exceed 2 cores.
5 Across all pods in a non-terminal state, the sum of memory limits cannot exceed 2Gi.
Example 4. besteffort.yaml
apiVersion: v1
kind: ResourceQuota
metadata:
  name: besteffort
spec:
  hard:
    pods: "1" (1)
  scopes:
  - BestEffort (2)
1 The total number of pods in a non-terminal state with BestEffort quality of service that can exist in the project.
2 Restricts the quota to only matching pods that have BestEffort quality of service for either memory or CPU.

Resources Managed by Quota

The following describes the set of compute resources and object types that may be managed by a quota.

Table 1. Compute Resources Managed by Quota
Resource Name Description

cpu

Across all pods in a non-terminal state, the sum of CPU requests 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.

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.

Table 2. Object Counts Managed by Quota
Resource Name Description

pods

The total number of pods in a non-terminal state that can exist in the project. 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 project.

resourcequotas

The total number of resource quotas that can exist in the project.

services

The total number of services that can exist in the project.

secrets

The total number of secrets that can exist in the project.

configmaps

The total number of ConfigMap objects that can exist in the project.

persistentvolumeclaims

The total number of persistent volume claims that can exist in the project.

openshift.io/imagestreams

The total number of image streams that can exist in the project.

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 a 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 for either cpu or memory.

NotBestEffort

Match pods that do not have best effort quality of service for cpu and memory.

A BestEffort scope restricts a quota to limit the following resources:

  • pods

A Terminating, NotTerminating, and NotBestEffort scope restricts a quota to tracking the following resources:

  • pods

  • memory

  • requests.memory

  • limits.memory

  • cpu

  • requests.cpu

  • limits.cpu

Quota Enforcement

After a resource quota for a project is first created, the project restricts the ability to create any new resources that may violate a quota constraint until it has calculated updated usage statistics.

After a quota is created and usage statistics are updated, the project accepts the creation of new content. When you create or modify resources, your quota usage is incremented immediately upon the request to create or modify the resource.

When you delete a resource, your quota use is decremented during the next full recalculation of quota statistics for the project. If project modifications exceed a quota usage limit, the server denies the action. An appropriate error message is returned explaining the quota constraint violated, and what your currently observed usage stats are in the system.

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.

See Compute Resources for more on setting requests and limits in pods and containers.

Limit Ranges

A limit range, defined by a LimitRange object, enumerates compute resource constraints in a project at the pod, container, image, image stream, and persistent volume claim level, and specifies the amount of resources that a pod, container, image, image stream, or persistent volume claim can consume.

All resource create and modification requests are evaluated against each LimitRange object in the project. If the resource violates any of the enumerated constraints, then the resource is rejected. If the resource does not set an explicit value, and if the constraint supports a default value, then the default value is applied to the resource.

Limit ranges are set by cluster administrators and are scoped to a given project.

Viewing Limit Ranges

You can view any limit ranges defined in a project by navigating in the web console to the project’s Settings tab.

You can also use the CLI to view limit range details:

  1. First, get the list of limit ranges defined in the project. For example, for a project called demoproject:

    $ oc get limits -n demoproject
    NAME              AGE
    resource-limits   6d
  2. Then, describe the limit range you are interested in, for example the resource-limits limit range:

    $ oc describe limits resource-limits
    Name:                     limits
    Namespace:                default
    Type                      Resource                 Min  Max Request Limit Limit/Request
    ----                      --------                 ---  --- ------- ----- -------------
    Pod                       memory                   6Mi  1Gi -       -     -
    Pod                       cpu                      200m  2  -       -     -
    Container                 cpu                      100m  2  200m    300m  10
    Container                 memory                   4Mi  1Gi 100Mi   200Mi -
    openshift.io/Image        storage                  -    1Gi -       -     -
    openshift.io/ImageStream  openshift.io/image-tags  -    10  -       -     -
    openshift.io/ImageStream  openshift.io/images      -    12  -       -     -

Full limit range definitions can be viewed by running oc export on the object. The following shows an example limit range definition:

Example 5. Core Limit Range Object Definition
apiVersion: "v1"
kind: "LimitRange"
metadata:
  name: "core-resource-limits" (1)
spec:
  limits:
    - type: "Pod"
      max:
        cpu: "2" (2)
        memory: "1Gi" (3)
      min:
        cpu: "200m" (4)
        memory: "6Mi" (5)
    - type: "Container"
      max:
        cpu: "2" (6)
        memory: "1Gi" (7)
      min:
        cpu: "100m" (8)
        memory: "4Mi" (9)
      default:
        cpu: "300m" (10)
        memory: "200Mi" (11)
      defaultRequest:
        cpu: "200m" (12)
        memory: "100Mi" (13)
      maxLimitRequestRatio:
        cpu: "10" (14)
1 The name of the limit range document.
2 The maximum amount of CPU that a pod can request on a node across all containers.
3 The maximum amount of memory that a pod can request on a node across all containers.
4 The minimum amount of CPU that a pod can request on a node across all containers.
5 The minimum amount of memory that a pod can request on a node across all containers.
6 The maximum amount of CPU that a single container in a pod can request.
7 The maximum amount of memory that a single container in a pod can request.
8 The minimum amount of CPU that a single container in a pod can request.
9 The minimum amount of memory that a single container in a pod can request.
10 The default amount of CPU that a container will be limited to use if not specified.
11 The default amount of memory that a container will be limited to use if not specified.
12 The default amount of CPU that a container will request to use if not specified.
13 The default amount of memory that a container will request to use if not specified.
14 The maximum amount of CPU burst that a container can make as a ratio of its limit over request.
Example 6. OpenShift Online Limit Range Object Definition
apiVersion: "v1"
kind: "LimitRange"
metadata:
  name: "openshift-resource-limits"
spec:
  limits:
    - type: openshift.io/Image
      max:
        storage: 1Gi (1)
    - type: openshift.io/ImageStream
      max:
        openshift.io/image-tags: 20 (2)
        openshift.io/images: 30 (3)
1 The maximum size of an image that can be pushed to an internal registry.
2 The maximum number of unique image tags per image stream’s spec.
3 The maximum number of unique image references per image stream’s status.

Both core and OpenShift Online resources can be specified in just one limit range object. They are separated here into two examples for clarity.

Container Limits

Supported Resources:

  • CPU

  • Memory

Supported Constraints:

Per container, the following must hold true if specified:

Table 3. Container
Constraint Behavior

Min

Min[resource] less than or equal to container.resources.requests[resource] (required) less than or equal to container/resources.limits[resource] (optional)

If the configuration defines a min CPU, then the request value must be greater than the CPU value. A limit value does not need to be specified.

Max

container.resources.limits[resource] (required) less than or equal to Max[resource]

If the configuration defines a max CPU, then you do not need to define a request value, but a limit value does need to be set that satisfies the maximum CPU constraint.

MaxLimitRequestRatio

MaxLimitRequestRatio[resource] less than or equal to ( container.resources.limits[resource] / container.resources.requests[resource])

If a configuration defines a maxLimitRequestRatio value, then any new containers must have both a request and limit value. Additionally, OpenShift Online calculates a limit to request ratio by dividing the limit by the request.

For example, if a container has cpu: 500 in the limit value, and cpu: 100 in the request value, then its limit to request ratio for cpu is 5. This ratio must be less than or equal to the maxLimitRequestRatio.

Supported Defaults:

Default[resource]

Defaults container.resources.limit[resource] to specified value if none.

Default Requests[resource]

Defaults container.resources.requests[resource] to specified value if none.

Pod Limits

Supported Resources:

  • CPU

  • Memory

Supported Constraints:

Across all containers in a pod, the following must hold true:

Table 4. Pod
Constraint Enforced Behavior

Min

Min[resource] less than or equal to container.resources.requests[resource] (required) less than or equal to container.resources.limits[resource] (optional)

Max

container.resources.limits[resource] (required) less than or equal to Max[resource]

MaxLimitRequestRatio

MaxLimitRequestRatio[resource] less than or equal to ( container.resources.limits[resource] / container.resources.requests[resource])

Compute Resources

Each container running on a node consumes compute resources, which are measurable quantities that can be requested, allocated, and consumed.

When authoring a pod configuration file, you can optionally specify how much CPU and memory (RAM) each container needs in order to better schedule pods in the cluster and ensure satisfactory performance.

CPU is measured in units called millicores. Each node in a cluster inspects the operating system to determine the amount of CPU cores on the node, then multiplies that value by 1000 to express its total capacity. For example, if a node has 2 cores, the node’s CPU capacity would be represented as 2000m. If you wanted to use 1/10 of a single core, it would be represented as 100m.

Memory is measured in bytes. In addition, it may be used with SI suffices (E, P, T, G, M, K) or their power-of-two-equivalents (Ei, Pi, Ti, Gi, Mi, Ki).

apiVersion: v1
kind: Pod
spec:
  containers:
  - image: nginx
    name: nginx
    resources:
      requests:
        cpu: 100m (1)
        memory: 200Mi (2)
      limits:
        cpu: 200m (3)
        memory: 400Mi (4)
1 The container requests 100m cpu.
2 The container requests 200Mi memory.
3 The container limits 200m cpu.
4 The container limits 400Mi memory.

CPU Requests

Each container in a pod can specify the amount of CPU it requests on a node. The scheduler uses CPU requests to find a node with an appropriate fit for a container.

The CPU request represents a minimum amount of CPU that your container may consume, but if there is no contention for CPU, it can use all available CPU on the node. If there is CPU contention on the node, CPU requests provide a relative weight across all containers on the system for how much CPU time the container may use.

On the node, CPU requests map to Kernel CFS shares to enforce this behavior.

In OpenShift Online, CPU requests are set automatically based on the memory limit specified. If no memory limit is specified, a CPU request of 60m is set.

Viewing Compute Resources

To view compute resources for a pod:

$ oc describe pod nginx-tfjxt
Name:       nginx-tfjxt
Namespace:      default
Image(s):     nginx
Node:       /
Labels:       run=nginx
Status:       Pending
Reason:
Message:
IP:
Replication Controllers:  nginx (1/1 replicas created)
Containers:
  nginx:
    Container ID:
    Image:    nginx
    Image ID:
    QoS Tier:
      cpu:  Burstable
      memory: Burstable
    Limits:
      cpu:  200m
      memory: 400Mi
    Requests:
      cpu:    100m
      memory:   200Mi
    State:    Waiting
    Ready:    False
    Restart Count:  0
    Environment Variables:

CPU Limits

Each container in a pod can specify the amount of CPU it is limited to use on a node. CPU limits control the maximum amount of CPU that your container may use independent of contention on the node. If a container attempts to exceed the specified limit, the system will throttle the container. This allows the container to have a consistent level of service independent of the number of pods scheduled to the node.

In OpenShift Online, CPU limits are set automatically based on the memory limit specified. If no memory limit is specified, a CPU limit of 1 core is set.

Memory Requests

By default, a container is able to consume as much memory on the node as possible. In order to improve placement of pods in the cluster, specify the amount of memory required for a container to run. The scheduler will then take available node memory capacity into account prior to binding your pod to a node. A container is still able to consume as much memory on the node as possible even when specifying a request.

In OpenShift Online, memory requests are set automatically based on the memory limit specified. If no memory limit is specified, a memory request of 307Mi is assumed.

Memory Limits

If you specify a memory limit, you can constrain the amount of memory the container can use. For example, if you specify a limit of 200Mi, a container will be limited to using that amount of memory on the node. If the container exceeds the specified memory limit, it will be terminated and potentially restarted dependent upon the container restart policy.

In OpenShift Online, the memory request, CPU request, and CPU limit will automatically be determined and set appropriately based off of the specified memory limit. If no memory limit is specified, a memory limit of 512Mi is assumed.

Quality of Service Tiers

A compute resource is classified with a quality of service (QoS) based on the specified request and limit value.

Quality of Service Description

BestEffort

Provided when a request and limit are not specified.

Burstable

Provided when a request is specified that is less than an optionally specified limit.

Guaranteed

Provided when a limit is specified that is equal to an optionally specified request.

A container may have a different quality of service for each compute resource. For example, a container can have Burstable CPU and Guaranteed memory qualities of service.

The quality of service has different impacts on different resources, depending on whether the resource is compressible or not. CPU is a compressible resource, whereas memory is an incompressible resource.

With CPU Resources:
  • A BestEffort CPU container is able to consume as much CPU as is available on a node but runs with the lowest priority.

  • A Burstable CPU container is guaranteed to get the minimum amount of CPU requested, but it may or may not get additional CPU time. Excess CPU resources are distributed based on the amount requested across all containers on the node.

  • A Guaranteed CPU container is guaranteed to get the amount requested and no more, even if there are additional CPU cycles available. This provides a consistent level of performance independent of other activity on the node.

With Memory Resources:
  • A BestEffort memory container is able to consume as much memory as is available on the node, but there are no guarantees that the scheduler will place that container on a node with enough memory to meet its needs. In addition, a BestEffort container has the greatest chance of being killed if there is an out of memory event on the node.

  • A Burstable memory container is scheduled on the node to get the amount of memory requested, but it may consume more. If there is an out of memory event on the node, Burstable containers are killed after BestEffort containers when attempting to recover memory.

  • A Guaranteed memory container gets the amount of memory requested, but no more. In the event of an out of memory event, it will only be killed if there are no more BestEffort or Burstable containers on the system.

Specifying Compute Resources via CLI

To specify compute resources via the CLI:

$ oc run nginx --image=nginx --limits=memory=400Mi

Opaque Integer Resources

Opaque integer resources allow cluster operators to provide new node-level resources that would be otherwise unknown to the system. Users can consume these resources in pod specifications, similar to CPU and memory. The scheduler performs resource accounting so that no more than the available amount is simultaneously allocated to pods.

Opaque integer resources are Alpha currently, and only resource accounting is implemented. There is no resource quota or limit range support for these resources, and they have no impact on QoS.

Opaque integer resources are called opaque because OpenShift Online does not know what the resource is, but will schedule a pod on a node only if enough of that resource is available. They are called integer resources because they must be available, or advertised, in integer amounts. The API server restricts quantities of these resources to whole numbers. Examples of valid quantities are 3, 3000m, and 3Ki.

The cluster administrator is usually responsible for creating the resources and making them available.

To consume an opaque integer resource in a pod, edit the pod to include the name of the opaque resource as a key in the spec.containers[].resources.requests field.

For example: The following pod requests two CPUs and one foo (an opaque resource).

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
spec:
  containers:
  - name: my-container
    image: myimage
    resources:
      requests:
        cpu: 2
        pod.alpha.kubernetes.io/opaque-int-resource-foo: 1

The pod will be scheduled only if all of the resource requests are satisfied (including CPU, memory, and any opaque resources). The pod will remain in the PENDING state while the resource request cannot be met by any node.

Conditions:
  Type    Status
  PodScheduled  False
...
Events:
  FirstSeen  LastSeen	Count	From		  SubObjectPath	Type	  Reason	    Message
  ---------  --------	-----	----		  -------------	--------  ------	    -------
  14s	     0s		6	default-scheduler		Warning	  FailedScheduling  No nodes are available that match all of the following predicates:: Insufficient pod.alpha.kubernetes.io/opaque-int-resource-foo (1).