通過一個實際例子理解Kubernetes里pod的自動scale - 水平自動伸縮

kubectl scale命令用于程序在負載加重或縮小時進行pod擴容或縮小，我們通過一些實際例子來觀察scale命令到底能達到什么效果。

命令行創建一個deployment：

kubectl run jerry-nginx --image=nginx:1.12.2

kubectl get deploy查看剛剛創建的deployment：

自動被deployment創建的pod：

kubectl get pod:

使用下列命令查看生成的deployment明細：

kubectl get deployment jerry-nginx -o yaml

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
annotations:
deployment.kubernetes.io/revision: "1"
creationTimestamp: 2018-11-29T08:29:06Z
generation: 1
labels:
run: jerry-nginx
name: jerry-nginx
namespace: part-0110
resourceVersion: "7203445"
selfLink: /apis/extensions/v1beta1/namespaces/part-0110/deployments/jerry-nginx
uid: d5c64f72-f3b0-11e8-b308-a20cb743f347
spec:
progressDeadlineSeconds: 600
replicas: 1
revisionHistoryLimit: 2
selector:
matchLabels:
run: jerry-nginx
strategy:
rollingUpdate:
maxSurge: 25%
maxUnavailable: 25%
type: RollingUpdate
template:
metadata:
creationTimestamp: null
labels:
run: jerry-nginx
spec:
containers:
- image: nginx:1.12.2
imagePullPolicy: IfNotPresent
name: jerry-nginx
resources: {}
terminationMessagePath: /dev/termination-log
terminationMessagePolicy: File
dnsPolicy: ClusterFirst
restartPolicy: Always
schedulerName: default-scheduler
securityContext: {}
terminationGracePeriodSeconds: 30
status:
availableReplicas: 1
conditions:

• lastTransitionTime: 2018-11-29T08:29:07Z
  lastUpdateTime: 2018-11-29T08:29:07Z
  message: Deployment has minimum availability.
  reason: MinimumReplicasAvailable
  status: "True"
  type: Available

• lastTransitionTime: 2018-11-29T08:29:06Z
  lastUpdateTime: 2018-11-29T08:29:07Z
  message: ReplicaSet "jerry-nginx-69fd9f6c4" has successfully progressed.
  reason: NewReplicaSetAvailable
  status: "True"
  type: Progressing
  observedGeneration: 1
  readyReplicas: 1
  replicas: 1
  updatedReplicas: 1

另一個有用的命令：

kubectl describe deployment jerry-nginx

Name: jerry-nginx
Namespace: part-0110
CreationTimestamp: Thu, 29 Nov 2018 16:29:06 +0800
Labels: run=jerry-nginx
Annotations: deployment.kubernetes.io/revision: 1
Selector: run=jerry-nginx
Replicas: 1 desired | 1 updated | 1 total | 1 available | 0 unavailable
StrategyType: RollingUpdate
MinReadySeconds: 0
RollingUpdateStrategy: 25% max unavailable, 25% max surge
Pod Template:
Labels: run=jerry-nginx
Containers:
jerry-nginx:
Image: nginx:1.12.2
Port: <none>
Host Port: <none>
Environment: <none>
Mounts: <none>
Volumes: <none>
Conditions:
Type Status Reason

Available True MinimumReplicasAvailable
Progressing True NewReplicaSetAvailable
OldReplicaSets: <none>
NewReplicaSet: jerry-nginx-69fd9f6c4 (1/1 replicas created)
Events:
Type Reason Age From Message

Normal ScalingReplicaSet 9m41s deployment-controller Scaled up replica set jerry-nginx-69fd9f6c4 to 1

現在我們使用下面的命令對deployment進行水平擴展：

kubectl scale deployment jerry-nginx --replicas=3

kubectl get pods -l run=jerry-nginx

下圖這個Age為15分鐘之前的是第一次創建deployment時生成的，其他兩個Age為1分鐘之前的是執行了scale命令后自動創建的。

選中一個才創建的pod，查看其事件記錄：

kubectl describe pod jerry-nginx-69fd9f6c4-8dpvb

kubectl get replicaset

得到自動創建的replication set：

desired = 3意思就是我們水平擴展時指定的參數3.

即使手動刪除一個pod實例，replication set又會很快自動創建一個新的：

自動創建的新pod：

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