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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