Setting Limit Ranges | Cluster Administration

Important

Azure Red Hat OpenShift 3.11 will be retired 30 June 2022. Support for creation of new Azure Red Hat OpenShift 3.11 clusters continues through 30 November 2020. Following retirement, remaining Azure Red Hat OpenShift 3.11 clusters will be shut down to prevent security vulnerabilities.

Follow this guide to create an Azure Red Hat OpenShift 4 cluster. If you have specific questions, please contact us

Purpose for Limit Ranges
Creating a Limit Range
Viewing a Limit
Deleting a Limit Range

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

For CPU and memory limits, if you specify a maximum value but do not specify a minimum limit, the resource can consume more CPU and memory resources than the maximum value.

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 object.
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. If you do not set a `min` value or you set `min` to `0`, the result is no limit and the pod can consume more than the `max` CPU value.
5	The minimum amount of memory that a pod can request on a node across all containers. If you do not set a `min` value or you set `min` to `0`, the result is no limit and the pod can consume more than the `max` memory value.
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. If you do not set a `min` value or you set `min` to `0`, the result is no limit and the pod can consume more than the `max` CPU value.
9	The minimum amount of memory that a single container in a pod can request. If you do not set a `min` value or you set `min` to `0`, the result is no limit and the pod can consume more than the `max` memory value.
10	The default CPU limit for a container if you do not specify a limit in the pod specification.
11	The default memory limit for a container if you do not specify a limit in the pod specification.
12	The default CPU request for a container if you do not specify a request in the pod specification.
13	The default memory request for a container if you do not specify a request in the pod specification.
14	The maximum limit-to-request ratio for a container.

For more information on how CPU and memory are measured, see Compute Resources.

Azure Red Hat OpenShift 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)
    - type: "Pod"
      max:
        cpu: "2" (4)
        memory: "1Gi" (5)
        ephemeral-storage: "1Gi" (6)
     max:
        cpu: "1" (7)
        memory: "1Gi" (8)

1	The maximum size of an image that can be pushed to an internal registry.
2	The maximum number of unique image tags as defined in the specification for the image stream.
3	The maximum number of unique image references as defined in the specification for the image stream status.
4	The maximum amount of CPU that a pod can request on a node across all containers.
5	The maximum amount of memory that a pod can request on a node across all containers.
6	The maximum amount of ephemeral storage that a pod can request on a node across all containers, if the ephemeral storage technology preview is enabled.
7	The minimum amount of CPU that a pod can request on a node across all containers. If you do set a `min` value or you set `min` to `0`, the result is no limit and the pod can consume more than the `max` CPU value.
8	The minimum amount of memory that a pod can request on a node across all containers. If you do not set a `min` value or you set `min` to `0`, the result` is no limit and the pod can consume more than the `max` memory value.

You can specify both core and Azure Red Hat OpenShift resources in one limit range object. They are shown separately in two examples for clarity.

Container Limits

Supported Resources:

CPU
Memory

Supported Constraints:

Per container, the following must hold true if specified:

Table 1. 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, the request value must be greater than the CPU value. If you do not set a `min` value or you set `min` to `0`, the result is no limit and the pod can consume more of the resource than the `max` value.
`Max`	`container.resources.limits[resource]` (required) less than or equal to `Max[resource]` If the configuration defines a `max` CPU, you do not need to define a CPU request value. However, you must set a limit that satisfies the maximum CPU constraint that is specified in the limit range.
`MaxLimitRequestRatio`	`MaxLimitRequestRatio[resource]` less than or equal to (`container.resources.limits[resource]` / `container.resources.requests[resource]`) If the limit range defines a `maxLimitRequestRatio` constraint, any new containers must have both a `request` and a `limit` value. Additionally, Azure Red Hat OpenShift calculates a limit-to-request ratio by dividing the `limit` by the `request`. The result should be an integer greater than 1. For example, if a container has `cpu: 500` in the `limit` value, and `cpu: 100` in the `request` value, the 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 2. 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]`. If you do not set a `min` value or you set `min` to `0`, the result is no limit and the pod can consume more of the resource than the `max` value.
`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]`).

Image Limits

Supported Resources:

Storage

Resource type name:

openshift.io/Image

Per image, the following must hold true if specified:

Table 3. Image
Constraint	Behavior
`Max`	`image.dockerimagemetadata.size` less than or equal to `Max[resource]`

The image size is not always available in the manifest of an uploaded image. This is especially the case for images built with Docker 1.10 or higher and pushed to a v2 registry. If such an image is pulled with an older Docker daemon, the image manifest is converted by the registry to schema v1 and does not include all the size information. No storage limit set on images will prevent it from being uploaded.

The issue is being addressed.

Image Stream Limits

Supported Resources:

openshift.io/image-tags
openshift.io/images

Resource type name:

openshift.io/ImageStream

Per image stream, the following must hold true if specified:

Table 4. ImageStream
Constraint	Behavior
`Max[openshift.io/image-tags]`	`length( uniqueimagetags( imagestream.spec.tags ) )` less than or equal to `Max[openshift.io/image-tags]` `uniqueimagetags` returns unique references to images of given spec tags.
`Max[openshift.io/images]`	`length( uniqueimages( imagestream.status.tags ) )` less than or equal to `Max[openshift.io/images]` `uniqueimages` returns unique image names found in status tags. The name is equal to the digest for the image.

Counting of Image References

The openshift.io/image-tags resource represents unique image references. Possible references are an ImageStreamTag, an ImageStreamImage, or a DockerImage. Tags can be created by using the oc tag and oc import-image commands or by using tag tracking. No distinction is made between internal and external references. However, each unique reference that is tagged in an image stream specification is counted just once. It does not restrict pushes to an internal container image registry in any way, but is useful for tag restriction.

The openshift.io/images resource represents unique image names that are recorded in image stream status. It allows for restriction of a number of images that can be pushed to the internal registry. Internal and external references are not distinguished.

PersistentVolumeClaim Limits

Supported Resources:

Storage

Supported Constraints:

Across all persistent volume claims in a project, the following must hold true:

Table 5. Pod
Constraint	Enforced Behavior
`Min`	Min[resource] <= claim.spec.resources.requests[resource] (required)
`Max`	claim.spec.resources.requests[resource] (required) <= Max[resource]

Limit Range Object Definition

{
  "apiVersion": "v1",
  "kind": "LimitRange",
  "metadata": {
    "name": "pvcs" (1)
  },
  "spec": {
    "limits": [{
        "type": "PersistentVolumeClaim",
        "min": {
          "storage": "2Gi" (2)
        },
        "max": {
          "storage": "50Gi" (3)
        }
      }
    ]
  }
}

1	The name of the limit range object.
2	The minimum amount of storage that can be requested in a persistent volume claim.
3	The maximum amount of storage that can be requested in a persistent volume claim.

Creating a Limit Range

To apply a limit range to a project:

Create a limit range object definition with your required specifications.

Create the object:

$ oc create -f <limit_range_file> -n <project>

Viewing a Limit

You can view any limit ranges that are defined in a project by navigating in the web console to the Quota page for the project.

You can also use the CLI to view limit range details by performing the following steps:

Get the list of limit range objects that are defined in the project. For example, for a project called demoproject:
```
$ oc get limits -n demoproject
```
Example Output
```
NAME              AGE
resource-limits   6d
```

Describe the limit range. For example, for a limit range called resource-limits:

$ oc describe limits resource-limits -n demoproject

Example Output

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

Deleting a Limit Range

To remove a limit range and no longer enforce the limits of a project:

Run the following command:
```
$ oc delete limits <limit_name>
```