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. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:
To check the version, enterkubectl version.
Each node in your cluster must have at least 2 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.
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 apply -f https://k8s.io/examples/admin/resource/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.
apiVersion: v1
kind: Pod
metadata:
name: default-mem-demo
spec:
containers:
- name: default-mem-demo-ctr
image: nginx
Create the Pod.
kubectl apply -f https://k8s.io/examples/admin/resource/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:
apiVersion: v1
kind: Pod
metadata:
name: default-mem-demo-2
spec:
containers:
- name: default-mem-demo-2-ctr
image: nginx
resources:
limits:
memory: "1Gi"
Create the Pod:
kubectl apply -f https://k8s.io/examples/admin/resource/memory-defaults-pod-2.yaml --namespace=default-mem-example
View detailed information about the Pod:
kubectl get pod default-mem-demo-2 --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:
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 apply -f https://k8s.io/examples/admin/resource/memory-defaults-pod-3.yaml --namespace=default-mem-example
View the Pod's specification:
kubectl get pod default-mem-demo-3 --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:
- Every Container that runs in the namespace must have its own memory limit.
- The total amount of memory used by all Containers in the namespace must not exceed a specified limit.
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.
Clean up
Delete your namespace:
kubectl delete namespace default-mem-example
What's next
For cluster administrators
-
Configure Minimum and Maximum Memory Constraints for a Namespace
-
Configure Minimum and Maximum CPU Constraints for a Namespace