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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%E6%BA%90%E7%A0%81%E5%AD%A6%E4%B9%A0-Controller-P1-%E5%A4%9A%E5%AE%9E%E4%BE%8Bleader%E9%80%89%E4%B8%BE.md](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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- [Kubernetes源码学习-Controller-P2-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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- [Kubernetes源码学习-Controller-P3-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 Controller.md)
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- [StafulSet Controller]
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- 待补充
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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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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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**功能模块**
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`kubernetes/src/k8s.io/kubernetes/pkg/controller`
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