Pod和容器的LimitRange原理和實踐總結

lightinglei發表於2021-01-29
MIT

一、背景介紹

通常情況下，Pod中的容器可以無限制的使用節點上的CPU和記憶體資源，在共享資源和資源有限的情況下，若不加以限制，某個叢集或名稱空間的資源可能會消耗殆盡，導致其他節點上優先順序低的Pod發生驅逐、重新排程、重啟等問題，因此針對資源限額需要有針對名稱空間級別的使用限制，以及針對Pod和容器級別的使用限制，LimitRange就是在後者的背景下誕生的。

二、應用場景

1、適用對叢集的某個名稱空間中的容器設定預設的統一的request和limit值，配合Resource Quotas更好的實現名稱空間級別的資源限額。

2、適用對單個Pod的CPU和記憶體資源限額控制，如實現Pod中所有容器CPUlimit之和不得超過某值。

3、適用對單個容器的CPU和記憶體資源限額控制，如實現容器的CPUlimit值不得超過某值。

三、實踐

一、LimitRange設定預設request和limit

適用場景：適用對叢集的某個名稱空間中的容器設定預設的統一的request和limit值

【新建limitrange】

LimitRange針對某個namespace的Pod或容器的CPU和記憶體的預設值、request和limit值實現管控，因此限制的的範圍是在namespace下，在建立LimitRange之前，先建立1個用於測試的namespace

 kubectl create namespace limitrange-test-ns
[root@k8s-master limitrange]# kubectl get ns |grep limitrange-test-ns
limitrange-test-ns   Active   78m

namespace建立成功後，在此名稱空間下建立limitrange

[root@k8s-master limitrange]# ls
limitrange.yaml
[root@k8s-master limitrange]# cat limitrange.yaml 
apiVersion: v1
kind: LimitRange
metadata:
  name: mem-limit-range-test
  namespace: limitrange-test-ns   #指定名稱空間
spec:
  limits:
  - default:
      memory: 256Mi               
    defaultRequest:
      memory: 128Mi
    type: Container
kubectl apply -f limitrange.yaml 
[root@k8s-master limitrange]# kubectl describe limitrange mem-limit-range-test -n limitrange-test-ns 
Name:       mem-limit-range-test
Namespace:  limitrange-test-ns
Type        Resource  Min  Max  Default Request  Default Limit  Max Limit/Request Ratio
----        --------  ---  ---  ---------------  -------------  -----------------------
Container   memory    -    -    128Mi            256Mi          -
[root@k8s-master limitrange]# kubectl describe ns limitrange-test-ns
Name:         limitrange-test-ns
Labels:       <none>
Annotations:  <none>
Status:       Active

No resource quota.

Resource Limits
 Type       Resource  Min  Max  Default Request  Default Limit  Max Limit/Request Ratio
 ----       --------  ---  ---  ---------------  -------------  -----------------------
 Container  memory    -    -    128Mi            256Mi          -

可以看到已為limitrange-test-ns的名稱空間下所有的容器設定了預設的request值和limit值，接下來看下在容器中是如何生效的

【容器limitrange生效驗證】

1、容器未設定limit，且未設定request

[root@k8s-master limitrange]# cat container-limitrange.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: pod-container-men-limit-test
spec:
  containers:
  - name: container-limlitrange-test
    image: nginx:latest
    imagePullPolicy: IfNotPresent
[root@k8s-master limitrange]# kubectl get pod -o wide -n limitrange-test-ns 
NAME                           READY   STATUS    RESTARTS   AGE   IP               NODE         NOMINATED NODE   READINESS GATES
pod-container-men-limit-test   1/1     Running   0          28s   10.122.235.216   k8s-master   <none>           <none>
[root@k8s-master limitrange]# curl 10.122.235.216:80
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
    body {
        width: 35em;
        margin: 0 auto;
        font-family: Tahoma, Verdana, Arial, sans-serif;
    }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

可以看到此Pod已經running，且業務正常，在建立此Pod容器部分並未設定預設值，但是Pod所在的名稱空間有配置過預設的limitrange策略，驗證下此策略是否生效到Pod的容器部分

spec:
  containers:
  - image: nginx:latest
    imagePullPolicy: IfNotPresent
    name: container-limlitrange-test
    resources:
      limits:
        memory: 256Mi
      requests:
        memory: 128Mi

總結：容器未設定limit，且未設定request，則容器執行起來後的request和limit值預設與limitrange type為container設定的request和limit的保持一致。

2、容器中設定limit，但是未設定request

[root@k8s-master limitrange]# cat container-limitrange.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: pod-container-men-limit-test
  namespace: limitrange-test-ns
spec:
  containers:
  - name: container-limlitrange-test
    image: nginx:latest
    imagePullPolicy: IfNotPresent
    resources:
      limits:
        memory: "500Mi"

只設定記憶體的limit值且大於limitrange設定的limit值

[root@k8s-master limitrange]# kubectl apply -f container-limitrange.yaml 
pod/pod-container-men-limit-test created
[root@k8s-master limitrange]# kubectl get pod -n limitrange-test-ns 
NAME                           READY   STATUS    RESTARTS   AGE
pod-container-men-limit-test   1/1     Running   0          9s
[root@k8s-master limitrange]# kubectl get pod pod-container-men-limit-test -o json -n limitrange-test-ns 
"spec": {
        "containers": [
            {
                "image": "nginx:latest",
                "imagePullPolicy": "IfNotPresent",
                "name": "container-limlitrange-test",
                "resources": {
                    "limits": {
                        "memory": "500Mi"
                    },
                    "requests": {
                        "memory": "500Mi"
                    }
                },
                "terminationMessagePath": "/dev/termination-log",
                "terminationMessagePolicy": "File"

總結：容器中設定實際limit，但是未設定request，容器執行成功後request=實際limit

3、容器中未設定limit，但是設定request

[root@k8s-master limitrange]# cat container-limitrange.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: pod-container-men-limit-test
  namespace: limitrange-test-ns
spec:
  containers:
  - name: container-limlitrange-test
    image: nginx:latest
    imagePullPolicy: IfNotPresent
    resources:
      requests:
        memory: "150Mi"
[root@k8s-master limitrange]# kubectl apply -f container-limitrange.yaml
pod/pod-container-men-limit-test created
[root@k8s-master limitrange]# kubectl get pod pod-container-men-limit-test -o json -n limitrange-test-ns
"spec": {
        "containers": [
            {
                "image": "nginx:latest",
                "imagePullPolicy": "IfNotPresent",
                "name": "container-limlitrange-test",
                "resources": {
                    "limits": {
                        "memory": "256Mi"
                    },
                    "requests": {
                        "memory": "150Mi"
                    }
                },
                "terminationMessagePath": "/dev/termination-log",
                "terminationMessagePolicy": "File",

總結：容器中未設定limit，但是設定實際request，則容器執行起來後request=實際request，limit=limitrange.limit

 

二、Pod和容器的max、min、maxLimitRequestRatio

適用場景：控制容器或Pod的CPU或記憶體資源使用，如容器的CPU的request不得小於多少，limit不得大於多少，不滿足條件則建立失敗，先介紹下引數：

容器部分：
1、defaultRequest：容器預設的request值，若不指定request值，則預設為此值

2、max：容器的實際設定的limit值應小於等於此值

3、min：容器實際設定的request值應大於等於此值

4、maxLimitRequestRatio：Max Limit/Request Ratio，為容器CPU或記憶體的Limit/Request值應小於等於此值

Pod部分：

1、max：Pod中所有容器的實際設定的limit之和值應小於等於此值

2、min：Pod中所有容器實際設定的request值之和應大於等於此值

3、maxLimitRequestRatio：Max Limit/Request Ratio，為Pod中所有容器CPU或記憶體的Limit之和/Request之和值應小於等於此值

演示如下：

 kubectl create namespace limitrange-02-test-ns
[root@k8s-master limitrange]# cat limitrange.yaml 
apiVersion: v1
kind: LimitRange
metadata:
  name: limitrange-test
  namespace: limitrange-02-test-ns 
spec:
 limits:
 - max:
    cpu: 2000m
    memory: 1000Mi
   min:
    cpu: 200m
    memory: 6Mi
   maxLimitRequestRatio:
    cpu: 3
    memory: 2
   type: Pod
 - default:                      #容器的預設limit值
    cpu: 300m
    memory: 200Mi
   defaultRequest:               #容器的預設request值
    cpu: 200m
    memory: 100Mi
   max:                          #容器的limit值不得大於max
    cpu: 1000m
    memory: 500Mi
   min:                          #容器的request的值不得小於min
    cpu: 100m
    memory: 3Mi
   maxLimitRequestRatio:         #容器的limit/request不得大於，如容器的CPU的limit/request不得大於4
    cpu: 5
    memory: 4
   type: Container
 kubectl apply -f container-02-limitrange.yaml 
[root@k8s-master limitrange]# kubectl describe ns limitrange-02-test-ns 
Name:         limitrange-02-test-ns
Labels:       <none>
Annotations:  <none>
Status:       Active

No resource quota.

Resource Limits
 Type       Resource  Min   Max     Default Request  Default Limit  Max Limit/Request Ratio
 ----       --------  ---   ---     ---------------  -------------  -----------------------
 Pod        cpu       200m  2       -                -              3
 Pod        memory    6Mi   1000Mi  -                -              2
 Container  cpu       100m  1       200m             300m           5
 Container  memory    3Mi   500Mi   100Mi            200Mi          4

可以看到設定的Pod和容器設定的max和min已經生效了，接下來驗證下設定的策略是否生效，建立1個Pod的容器的記憶體limit值大於500Mi

[root@k8s-master limitrange]# cat container-02-limitrange.yaml
apiVersion: v1
kind: Pod
metadata:
name: pod-limitrange-test
namespace: limitrange-02-test-ns
spec:
containers:
- name: container-limlitrange-test
image: nginx:latest
imagePullPolicy: IfNotPresent
resources:
requests:
memory: "100Mi"
limits:
memory: "600Mi"



[root@k8s-master limitrange]# kubectl apply -f container-02-limitrange.yaml 
Error from server (Forbidden): error when creating "container-02-limitrange.yaml": pods "pod-limitrange-test" is forbidden: [memory max limit to request ratio per Pod is 2, but provided ratio is 6.000000, maximum memory usage per Container is 500Mi, but limit is 600Mi, memory max limit to request ratio per Container is 4, but provided ratio is 6.000000]




提示容器的limit/request值為6大於4，且limit為600Mi大於設定最大max值500Mi，因此建立失敗，在Pod只有1個容器的情況下podlimit/request值為6大於2，同樣做下request值小於min值的測試




[root@k8s-master limitrange]# cat container-02-limitrange.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: pod-limitrange-test
  namespace: limitrange-02-test-ns
spec:
  containers:
  - name: container-limlitrange-test
    image: nginx:latest
    imagePullPolicy: IfNotPresent
    resources:
      requests:
        memory: "1Mi"    #小於min值
      limits:
        memory: "200Mi






[root@k8s-master limitrange]# kubectl apply -f container-02-limitrange.yaml 
Error from server (Forbidden): error when creating "container-02-limitrange.yaml": pods "pod-limitrange-test" is forbidden: [minimum memory usage per Pod is 6Mi, but request is 1048576, memory max limit to request ratio per Pod is 2, but provided ratio is 200.000000, minimum memory usage per Container is 3Mi, but request is 1Mi, memory max limit to request ratio per Container is 4, but provided ratio is 200.000000]




提示容器request的值為1Mi小於min值3Mi，且limit/request=200大於4，同樣不滿足Pod的min為6和ratio，因此建立失敗。


 四、總結


 本文描述了LimitRange的誕生背景、適用場景、以及具體如何實現和控制Pod、容器的資源限額，產品設計上主要考慮如下幾點：


1、產品設計上需要方便使用者低門檻快速設定預設request、limit值，配合Resource Quotas提供強大而穩定的K8S原生資源限額能力。


2、max、min、Limit/Request Ratio等功能如果開放給對K8S不瞭解的使用者，門檻較高，若無意配置完成且生效，可能會導致容器的建立異常，且不知如何解決，是否直接開放需要認真考慮。


 


 


 






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