命名空间中运行的容器使用的内存的最小值和最大值。 你可以在 LimitRange 对象中指定最小和最大内存值。如果 Pod 不满足 LimitRange 施加的约束，则无法在命名空间中创建它。

• 创建namespace

kubectl create namespace test

• 编写LimitRange 对象文件

  
  apiVersion: v1
  kind: LimitRange
  metadata:
    name: mem-min-demo
    namespace: test
  spec:
    limits:
    - max:
        memory: 1Gi
      min:
        memory: 500Mi
      type: Container

  可以看到内存的最大限制是1GB，最小请求500MB

注：如果不知道apiVersion版本，可以使用一下命令查看 kubectl  explain limitrange

[root@master-2-4 kubernetes]# kubectl explain limitrange
KIND:     LimitRange
VERSION:  v1

DESCRIPTION:
     LimitRange sets resource usage limits for each kind of resource in a
     Namespace.

FIELDS:
   apiVersion   <string>
     APIVersion defines the versioned schema of this representation of an
     object. Servers should convert recognized schemas to the latest internal
     value, and may reject unrecognized values. More info:
     https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#resources

   kind <string>
     Kind is a string value representing the REST resource this object
     represents. Servers may infer this from the endpoint the client submits
     requests to. Cannot be updated. In CamelCase. More info:
     https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#types-kinds

   metadata     <Object>
     Standard object's metadata. More info:
     https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata

   spec <Object>
     Spec defines the limits enforced. More info:
     https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status

• 使用pod测试

1. 尝试创建一个超出内存限制的pod

apiVersion: v1
kind: Pod
metadata:
  name: nginx
  namespace: test
spec:
  containers:
  - name: nginx
    image: nginx:1.20
    imagePullPolicy: IfNotPresent
    resources:
      limits:
        memory: 1800Mi
      requests:
        memory: 500Mi

[root@master-2-4 kubernetes]# kubectl apply -f nginx.yaml
Error from server (Forbidden): error when creating "nginx.yaml": pods "nginx" is forbidden: maximum memory usage per Container is 1Gi, but limit is 1800Mi

输出结果显示 Pod 没有创建成功，因为容器声明的内存限制太大了 

  2. 尝试创建一个小于内存限制的pod

apiVersion: v1
kind: Pod
metadata:
  name: nginx
  namespace: test
spec:
  containers:
  - name: nginx
    image: nginx:1.20
    imagePullPolicy: IfNotPresent
    resources:
      limits:
        memory: 600Mi
      requests:
        memory: 300Mi

[root@master-2-4 kubernetes]# kubectl apply -f nginx.yaml
Error from server (Forbidden): error when creating "nginx.yaml": pods "nginx" is forbidden: minimum memory usage per Container is 500Mi, but request is 300Mi

 输出结果显示 Pod 没有创建成功，因为容器声明的内存请求太小了

设置内存最小和最大限制的动因

作为集群管理员，你可能想规定 Pod 可以使用的内存总量限制。例如：

• 集群的每个节点有 2 GB 内存。你不想接受任何请求超过 2 GB 的 Pod，因为集群中没有节点可以满足。
• 集群由生产部门和开发部门共享。允许产品部门的负载最多耗用 8 GB 内存， 但是开发部门的负载最多可使用 512 MiB。 这时，可以为产品部门和开发部门分别创建名字空间，并为各个名字空间设置内存约束。