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: Deploymentmetadata: 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-a20cb743f347spec: 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-nginxspec:  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-0110CreationTimestamp: Thu, 29 Nov 2018 16:29:06 +0800Labels: run=jerry-nginxAnnotations: deployment.kubernetes.io/revision: 1Selector: run=jerry-nginxReplicas: 1 desired | 1 updated | 1 total | 1 available | 0 unavailableStrategyType: RollingUpdateMinReadySeconds: 0RollingUpdateStrategy: 25% max unavailable, 25% max surgePod Template: Labels: run=jerry-nginx Containers: jerry-nginx:

Image:        nginx:1.12.2Port:         
    
     Host Port:    
     
      Environment:  
      
       Mounts:       
       
      
     
    

Volumes:

Conditions: Type Status Reason ---- ------ ------ Available True MinimumReplicasAvailable Progressing True NewReplicaSetAvailableOldReplicaSets: 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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