第 11 屆 iThome 鐵人賽

DAY 15

DevOps

Kubernetes的30天養成計劃系列第 15 篇

[Day15] k8s管理篇（二）：Resource Quota、Namespaces

11th鐵人賽

Nick

團隊G8 Hash - c98b82371573afc08575815d90f5eac4

2019-09-30 16:13:54

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前言

今天我們要來了解關於Resource Quota，也就是資源配額、資源分配的設定方式，在限制使用的設定上，我們可以利用這個元件去限制CPU、記憶體、GPU、磁碟空間等等。再來是Namespace的部分，命名空間，我們可以自行定義，並結合Resource Quota，藉以達到將集群的資源分群的效果，會先一併介紹兩個概念，並套用整合的例子。

Resource Quota

資源配額，顧名思義是指在集群中能夠分配的資源，其實這段內容的一小部分在前面有稍微提過，主要是在介紹Pod和Deployment的時候。我們會在這邊進一步了解request和limit的詳細設定。

Namespaces

命名空間可以視為在k8s中的虛擬集群，它們底層依賴於同一個物理集群，有幾個特性：

命名空間為名稱提供了一個範圍。資源的名稱需要在命名空間內是惟一的，但不能跨命名空間。命名空間不能嵌套在另外一個命名空間內，而且每個k8s資源只能屬於一個命名空間。
命名空間是在多個用戶之間劃分集群資源的一種方法（通過資源配額）。
不需要使用多個命名空間來分隔輕微不同的資源，例如同一軟件的不同版本：使用Label（標籤）來區分同一命名空間中的不同資源。

整合範例

看完了前面兩個介紹，結合一起做一些例子方便理解：

新增一個YAML

$vim resourcequota.yaml
apiVersion: v1
kind: Namespace
metadata:
  name: myspace
---
apiVersion: v1
kind: ResourceQuota
metadata:
  name: compute-quota
  namespace: myspace
spec:
  hard:
    requests.cpu: "1"
    requests.memory: 1Gi
    requests.nvidia.com/gpu: 1
    limits.cpu: "2"
    limits.memory: 2Gi
    limits.nvidia.com/gpu: 2
---
apiVersion: v1
kind: ResourceQuota
metadata:
  name: object-quota
  namespace: myspace
spec:
  hard:
    configmaps: "10"
    persistentvolumeclaims: "4"
    replicationcontrollers: "20"
    secrets: "10"
    services: "10"
    services.loadbalancers: "2"

新增Resource Quota

$kubectl create -f resourcequota.yaml
namespace/myspace created
resourcequota/compute-quota created
resourcequota/object-quota created

示例一：沒有Resource Quota的Deployment

編輯一個沒有設置Resource Quota的Deployment

$vim helloworld-no-quotas.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: helloworld-deployment
  namespace: myspace
spec:
  replicas: 3
  selector:
    matchLabels:
      app: helloworld
  template:
    metadata:
      labels:
        app: helloworld
    spec:
      containers:
      - name: k8s-demo
        image: 105552010/k8s-demo
        ports:
        - name: nodejs-port
          containerPort: 3000

接著執行它

$kubectl apply -f helloworld-no-quotas.yaml
deployment.apps/helloworld-deployment created

檢查集群狀態

$kubectl get all -n myspace
NAME                                    READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/helloworld-deployment   0/3     0            0           104s

NAME                                               DESIRED   CURRENT   READY   AGE
replicaset.apps/helloworld-deployment-649949477d   3         0         0       104s

顯然資源調度有問題，Deployment沒有完全開起來

用Describe詳細看一下ReplicaSet

$kubectl describe replicaset.apps/helloworld-deployment-649949477d -n myspace
Name:           helloworld-deployment-649949477d
Namespace:      myspace
Selector:       app=helloworld,pod-template-hash=649949477d
Labels:         app=helloworld
                pod-template-hash=649949477d
Annotations:    deployment.kubernetes.io/desired-replicas: 3
                deployment.kubernetes.io/max-replicas: 4
                deployment.kubernetes.io/revision: 1
Controlled By:  Deployment/helloworld-deployment
Replicas:       0 current / 3 desired
Pods Status:    0 Running / 0 Waiting / 0 Succeeded / 0 Failed
Pod Template:
  Labels:  app=helloworld
           pod-template-hash=649949477d
  Containers:
   k8s-demo:
    Image:        105552010/k8s-demo
    Port:         3000/TCP
    Host Port:    0/TCP
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Conditions:
  Type             Status  Reason
  ----             ------  ------
  ReplicaFailure   True    FailedCreate
Events:
  Type     Reason        Age                    From                   Message
  ----     ------        ----                   ----                   -------
  Warning  FailedCreate  8m38s                  replicaset-controller  Error creating: pods 
"helloworld-deployment-649949477d-jg64g" is forbidden: failed quota: compute-quota: 
must specify limits.cpu,limits.memory,requests.cpu,requests.memory

注意Event的地方，它是說沒有在Deployment裡面定義limit和request那些，所以不能用。

也就是說，當一個集群有分配ResourceQuota和對應的Namespace時，所有在該集群內使用元件時必須都要詳細指明用量，不然不給用！

示例二：有Resource Quota的Deployment

我們再試個例子，有ResourceQuota設置的Deployment

$vim helloworld-with-quotas.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: helloworld-deployment
  namespace: myspace
spec:
  replicas: 3
  selector:
    matchLabels:
      app: helloworld
  template:
    metadata:
      labels:
        app: helloworld
    spec:
      containers:
      - name: k8s-demo
        image: 105552010/k8s-demo
        ports:
        - name: nodejs-port
          containerPort: 3000
        resources:
          requests:
            cpu: 200m
            memory: 0.5Gi
          limits:
            cpu: 400m
            memory: 1Gi

注意到增加了resources這個區塊，其中的request是初始化跟系統要的資源，而limit則是最大允許用量。

啟動它

$kubectl apply -f helloworld-with-quotas.yaml
deployment.apps/helloworld-deployment created

檢查相關狀態

$kubectl get all -n myspace
NAME                                         READY   STATUS    RESTARTS   AGE
pod/helloworld-deployment-5d87f4fbbf-rdsx7   1/1     Running   0          40s
pod/helloworld-deployment-5d87f4fbbf-ttszb   1/1     Running   0          40s

NAME                                    READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/helloworld-deployment   2/3     2            2           40s

NAME                                               DESIRED   CURRENT   READY   AGE
replicaset.apps/helloworld-deployment-5d87f4fbbf   3         2         2       40s

還少一個沒開起來，檢查下ResourceQuota

$kubectl get resourcequotas -n myspace
NAME            CREATED AT
compute-quota   2019-09-29T16:32:49Z
object-quota    2019-09-29T16:32:49Z
$kubectl describe resourcequotas -n myspace
Name:                    compute-quota
Namespace:               myspace
Resource                 Used    Hard
--------                 ----    ----
limits.cpu               600m    2
limits.memory            1536Mi  2Gi
limits.nvidia.com/gpu    0       2
requests.cpu             300m    1
requests.memory          768Mi   1Gi
requests.nvidia.com/gpu  0       1


Name:                   object-quota
Namespace:              myspace
Resource                Used  Hard
--------                ----  ----
configmaps              0     10
persistentvolumeclaims  0     4
replicationcontrollers  0     20
secrets                 1     10
services                0     10
services.loadbalancers  0     2

接著檢查Pod狀態

$kubectl describe replicasets.apps -n myspace
Name:           helloworld-deployment-5d87f4fbbf
Namespace:      myspace
Selector:       app=helloworld,pod-template-hash=5d87f4fbbf
Labels:         app=helloworld
                pod-template-hash=5d87f4fbbf
Annotations:    deployment.kubernetes.io/desired-replicas: 3
                deployment.kubernetes.io/max-replicas: 4
                deployment.kubernetes.io/revision: 1
Controlled By:  Deployment/helloworld-deployment
Replicas:       2 current / 3 desired
Pods Status:    2 Running / 0 Waiting / 0 Succeeded / 0 Failed
Pod Template:
  Labels:  app=helloworld
           pod-template-hash=5d87f4fbbf
  Containers:
   k8s-demo:
    Image:      105552010/k8s-demo
    Port:       3000/TCP
    Host Port:  0/TCP
    Limits:
      cpu:     400m
      memory:  1Gi
    Requests:
      cpu:        200m
      memory:     512Mi
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Conditions:
  Type             Status  Reason
  ----             ------  ------
  ReplicaFailure   True    FailedCreate
Events:
  Type     Reason            Age                    From                   Message
  ----     ------            ----                   ----                   -------
  Normal   SuccessfulCreate  3m35s                  replicaset-controller  Created pod: helloworld-deployment-5d87f4fbbf-ttszb
  Warning  FailedCreate      3m35s                  replicaset-controller  Error creating: pods "helloworld-deployment-5d87f4fbbf-h7krq" is forbidden: exceeded quota: 
compute-quota, requested: limits.memory=1Gi,requests.memory=512Mi, used: limits.memory=2Gi,requests.memory=1Gi, limited: limits.memory=2Gi,requests.memory=1Gi

顯然資源不夠分，因為ReplicaSet是3，如果3個開滿會吃到3G的記憶體，但是現在限制是2G

刪掉這個Deployment

$kubectl delete -f helloworld-with-quotas.yaml
deployment.apps "helloworld-deployment" deleted

示例三：Limit Range搭配沒有Resource Quota的Deployment

新增一個Limit Range

$vim defaults.yaml
apiVersion: v1
kind: LimitRange
metadata:
  name: limits
  namespace: myspace
spec:
  limits:
  - default:
      cpu: 200m
      memory: 512Mi
    defaultRequest:
      cpu: 100m
      memory: 256Mi
    type: Container

啟動它

$kubectl create -f defaults.yaml
limitrange/limits created

檢查Limit Range狀態

$kubectl describe limitranges -n myspace
Name:       limits
Namespace:  myspace
Type        Resource  Min  Max  Default Request  Default Limit  Max Limit/Request Ratio
----        --------  ---  ---  ---------------  -------------  -----------------------
Container   cpu       -    -    100m             200m           -
Container   memory    -    -    256Mi            512Mi          -

啟動沒有Resource Quota的Deployment

$kubectl create -f helloworld-no-quotas.yaml
deployment.apps/helloworld-deployment created

檢查myspace的集群狀態

$kubectl get all -n myspace
NAME                                         READY   STATUS    RESTARTS   AGE
pod/helloworld-deployment-649949477d-bxwf7   1/1     Running   0          81s
pod/helloworld-deployment-649949477d-h7rlb   1/1     Running   0          81s
pod/helloworld-deployment-649949477d-qznl2   1/1     Running   0          81s

NAME                                    READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/helloworld-deployment   3/3     3            3           81s

NAME                                               DESIRED   CURRENT   READY   AGE
replicaset.apps/helloworld-deployment-649949477d   3         3         3       81s

如果Namespace沒有要用的話，可以

$kubectl delete namespaces myspace
namespace "myspace" deleted

這樣就會把myspace底下所有相關的資源一併刪除。

OK，測試成功！

小結

今天我們學習到了Resource Quota，發現到除了在Pod和Deployment內可以定義外，這是一個全域定義的設置，只要在集群內沒有定義這個的就不能啟動，達到整合集群的管理資源效果。我們也看到了Namespace，一個命名空間，實際上的意義是虛擬群集，它有效的將原先集群內部的範圍做了很好的劃分，最後我們看了幾個整合應用，知道了Resource Quota可以搭配Namespace來使用，這樣的做法可以有效的區分不同虛擬群集的資源分配工作。