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Configure Default Memory Requests and Limits for a Namespace

This page shows how to configure default memory requests and limits for a namespace. If a Container is created in a namespace that has a default memory limit, and the Container does not specify its own memory limit, then the Container is assigned the default memory limit. Kubernetes assigns a default memory request under certain conditions that are explained later in this topic.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:

Each node in your cluster must have at least 300 GiB of memory.

Create a namespace

Create a namespace so that the resources you create in this exercise are isolated from the rest of your cluster.

kubectl create namespace default-mem-example

Create a LimitRange and a Pod

Here’s the configuration file for a LimitRange object. The configuration specifies a default memory request and a default memory limit.

memory-defaults.yaml
apiVersion: v1
kind: LimitRange
metadata:
  name: mem-limit-range
spec:
  limits:
  - default:
      memory: 512Mi
    defaultRequest:
      memory: 256Mi
    type: Container

Create the LimitRange in the default-mem-example namespace:

kubectl create -f https://k8s.io/docs/tasks/administer-cluster/memory-defaults.yaml --namespace=default-mem-example

Now if a Container is created in the default-mem-example namespace, and the Container does not specify its own values for memory request and memory limit, the Container is given a default memory request of 256 MiB and a default memory limit of 512 MiB.

Here’s the configuration file for a Pod that has one Container. The Container does not specify a memory request and limit.

memory-defaults-pod.yaml
apiVersion: v1
kind: Pod
metadata:
  name: default-mem-demo
spec:
  containers:
  - name: default-mem-demo-ctr
    image: nginx

Create the Pod.

kubectl create -f https://k8s.io/docs/tasks/administer-cluster/memory-defaults-pod.yaml --namespace=default-mem-example

View detailed information about the Pod:

kubectl get pod default-mem-demo --output=yaml --namespace=default-mem-example

The output shows that the Pod’s Container has a memory request of 256 MiB and a memory limit of 512 MiB. These are the default values specified by the LimitRange.

containers:
- image: nginx
  imagePullPolicy: Always
  name: default-mem-demo-ctr
  resources:
    limits:
      memory: 512Mi
    requests:
      memory: 256Mi

Delete your Pod:

kubectl delete pod default-mem-demo --namespace=default-mem-example

What if you specify a Container’s limit, but not its request?

Here’s the configuration file for a Pod that has one Container. The Container specifies a memory limit, but not a request:

memory-defaults-pod-2.yaml
apiVersion: v1
kind: Pod
metadata:
  name: default-mem-demo-2
spec:
  containers:
  - name: defalt-mem-demo-2-ctr
    image: nginx
    resources:
      limits:
        memory: "1Gi"

Create the Pod:

kubectl create -f https://k8s.io/docs/tasks/administer-cluster/memory-defaults-pod-2.yaml --namespace=default-mem-example

View detailed information about the Pod:

kubectl get pod mem-limit-no-request --output=yaml --namespace=default-mem-example

The output shows that the Container’s memory request is set to match its memory limit. Notice that the Container was not assigned the default memory request value of 256Mi.

resources:
  limits:
    memory: 1Gi
  requests:
    memory: 1Gi

What if you specify a Container’s request, but not its limit?

Here’s the configuration file for a Pod that has one Container. The Container specifies a memory request, but not a limit:

memory-defaults-pod-3.yaml
apiVersion: v1
kind: Pod
metadata:
  name: default-mem-demo-3
spec:
  containers:
  - name: default-mem-demo-3-ctr
    image: nginx
    resources:
      requests:
        memory: "128Mi"

Create the Pod:

kubectl create -f https://k8s.io/docs/tasks/administer-cluster/memory-defaults-pod-3.yaml --namespace=default-mem-example

View the Pod’s specification:

kubectl get pod default-mem-request-no-limit --output=yaml --namespace=default-mem-example

The output shows that the Container’s memory request is set to the value specified in the Container’s configuration file. The Container’s memory limit is set to 512Mi, which is the default memory limit for the namespace.

resources:
  limits:
    memory: 512Mi
  requests:
    memory: 128Mi

Motivation for default memory limits and requests

If your namespace has a resource quota, it is helpful to have a default value in place for memory limit. Here are two of the restrictions that a resource quota imposes on a namespace:

If a Container does not specify its own memory limit, it is given the default limit, and then it can be allowed to run in a namespace that is restricted by a quota.

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