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## Controller源码分段阅读导航
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- [多实例leader选举](https://github.com/yinwenqin/kubeSourceCodeNote/blob/master/controller/Kubernetes源码学习-Controller-P1-多实例leader选举.md)
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- [Controller与informer](https://github.com/yinwenqin/kubeSourceCodeNote/blob/master/controller/Kubernetes源码学习-Controller-P2-Controller与informer.md)
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- [Controller分类与Deployment Controller](https://github.com/yinwenqin/kubeSourceCodeNote/blob/master/controller/Kubernetes源码学习-Controller-P3-Controller分类与Deployment%20Controller.md)
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- [ReplicaSet Controller](https://github.com/yinwenqin/kubeSourceCodeNote/blob/master/controller/Kubernetes源码学习-Controller-P4-ReplicaSet%20Controller.md)
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- [StatefulSet Controller](https://github.com/yinwenqin/kubeSourceCodeNote/blob/master/controller/Kubernetes源码学习-Controller-P5-StatefulSet%20Controller.md)
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## 概述
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### kube-controller的作用
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**引述**
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首先依照惯例,贴两篇官方对 于controller的设计逻辑和运行机制的说明文档:
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https://github.com/kubernetes/community/blob/master/contributors/devel/sig-api-machinery/controllers.md
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https://github.com/kubernetes/community/blob/master/contributors/design-proposals/apps/controller_history.md
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**Controller是做什么用的?**
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Controller通过watch apiServer,循环地观察监控着某些特定的资源对象,获取它们当前的状态,对它们进行对比、修正、收敛,来使这些对象的状态不断靠近、直至达成在它们的声明语义中所期望的目标状态,这即是controller的作用。再通俗点来说,就是使资源对象的status当前状态达到spec的期望状态。
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**伪代码**
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一个简单的controller工作模式的伪代码示例:
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```go
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for {
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// 期望状态
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desired := getDesiredState()
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// 当前状态
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current := getCurrentState()
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// 使当前状态达到期望状态
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makeChanges(desired, current)
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}
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```
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### kube-controller的组成
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kube-controller是一个控制组件,根据我们的使用经验,有多种经常使用的资源,都不是实际地直接进行任务计算的资源类型,而在申明之后由k8s自动发现并保证以达成申明语义状态的逻辑资源,例如deployment、statefulSet、pvc、endpoint等,这些资源都分别由对应的controller子组件,那么这样的controller子组件有多少呢?如下图:
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![](http://mycloudn.wqyin.cn/20191206111312.jpg)
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可见controller的组件数量是非常之多的,因此在本部分中计划只抽选其中的deploymentController和statefulSetController这两种常见的对pod管理类型资源对应的controller来进行源码分析。
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### 代码结构
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**启动入口**
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`kubernetes/src/k8s.io/kubernetes/cmd/kube-controller-manager/controller-manager.go`
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![](http://mycloudn.wqyin.cn/20191206153026.jpg)
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**功能模块**
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`kubernetes/src/k8s.io/kubernetes/pkg/controller`
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![](http://mycloudn.wqyin.cn/20191206154051.jpg)
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