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
```sd

得到自动创建的replication set：
![](http://upload-images.jianshu.io/upload_images/2085791-45813c64aa3268be.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)


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：
![](http://upload-images.jianshu.io/upload_images/2085791-834fe8ffcc36a8d1.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)


自动创建的新pod：
![](http://upload-images.jianshu.io/upload_images/2085791-c9aae3be6cf247cc.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)

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