通过一个实际例子理解Kubernetes里pod的自动scale - 水平自动伸缩

kubectl scale命令用于程序在负载加重或缩小时进行pod扩容或缩小，我们通过一些实际例子来观察scale命令到底能达到什么效果。

命令行创建一个deployment：

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

kubectl get deploy查看刚刚创建的deployment：

自动被deployment创建的pod：

kubectl get pod:

使用下列命令查看生成的deployment明细：

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

另一个有用的命令：

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:

Host Port:

Environment:

Mounts:

Volumes:

Conditions:

Type Status Reason

---

Available True MinimumReplicasAvailable

Progressing True NewReplicaSetAvailable

OldReplicaSets:

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

现在我们使用下面的命令对deployment进行水平扩展：

kubectl scale deployment jerry-nginx --replicas=3

kubectl get pods -l run=jerry-nginx

下图这个Age为15分钟之前的是第一次创建deployment时生成的，其他两个Age为1分钟之前的是执行了scale命令后自动创建的。

选中一个才创建的pod，查看其事件记录：

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

kubectl get replicaset

得到自动创建的replication set：

desired = 3意思就是我们水平扩展时指定的参数3.

即使手动删除一个pod实例，replication set又会很快自动创建一个新的：

自动创建的新pod：

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