If you are not familiar with the oc command, refer to OpenShift - Getting Started with the oc command.

• Limits can be used to set the minimum and maximum amount of CPU/memory/storage for:
  • a single deployment related asset (e.g. container / pod) in a namespace and is typically defined in deployment YAML or deployment config YAML
  • all deployment related assets (e.g. containers / pods) in a namespace
• Quotas can be used to:
  • set the maximum amount of CPU and memory that can be used in a namespace
  • set the maximum number of running resources (e.g. persistent volume claims, pods, replication controllers, routes, secrets, services, et cetera) in a namespace
• Cluster Resource Quotas is the same as Quotas except the minimum and maximum are associated with:
  • A user
  • One or more namespaces

You can set both requests and limits.

• requests
  • ​the amount of memory / CPU that is reserved or allocated for the container.
• limit
  • ​the maximum amount of memory / CPU a container can use
  • if a container reaches the CPU limit, the container will be throttled (won’t let it consume any more CPU)
  • if a container reaches the memory limit, Out Of Memory (OOM) should occur and the pod should be killed
  • if a container reaches the storage limit, the pod should be evicted

This will set the combined CPU and memory limits of all of the containers or pods in a project. If you want to limit the CPU and memory for a single single deployment / container / pod in a namespace, refer to Deploy an application with CPU Memory limits using a YAML template file.

Before setting limits, you may want to view the pods Metrics in the OpenShift console at Workloads > pods > pod > Metrics to get a general idea the amount of memory and CPU being used by the pod.

A  JSON or YAML file that contains key value pairs used to create an object, such as a config map, deployment, a project, a pod, a route, a secret, a service, et cetera. These files are known as templates. The oc explain command can be used to get the list of keys that can be used in the JSON or YAML template file.

oc explain limitrange

And then more details on each key can be displayed.

oc explain limitrange.spec

For example, let's say you have a YAML file named limits.yml that contains the following markup.

apiVersion: v1
kind: LimitRange
metadata:
  name: my-limits
spec:
  limits:
    - type: Pod
      max:
        cpu: 20m
        memory: 1Gi
      min:
        cpu: 200m
        memory: 6Mi
    - type: Container
      max:
        cpu: 2
        memory: 1Gi
      min:
        cpu: 100m
        memory: 4Mi
      default:
        cpu: 300m
        memory: 200Mi
      defaultRequest:
        cpu: 200m
        memory: 100Mi
      maxLimitRequestRatio:
        cpu: 10m

The oc apply or oc create command with the -f or --filename option can be used to create the limits using the template JSON or YAML file.

The oc replace command can be used to replace limits using a new or updated template JSON or YAML file.

The oc edit command can be used to update a limits template YAML file.

~]$ oc create --filename limits.yml
limitrange/my-limits created

The oc get limits command can be used to list the limits that have been created in the current project / namespace.

~]$ oc get limits
NAME          CREATED AT
my-limits     2022-07-26T12:25:53Z

The oc describe limits command can be used to display more details about a limit.

• requests - the minimum of CPU/memory that is reserved or allocated for the container
• limits - the maximum amount of CPU/memory that can be used by the container

~]$ oc describe limits my-limits
Name:       my-limits
Namespace:  foo
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          -

And in the OpenShift console, you should see a dotted line representing the limit. I tend to noticed that memory is never exceeded but CPU can be forgiving, where a pod may exceeded the max CPU limit.