Kubernetes核心组件和架构图
Kubernetes核心组件和架构图(1)先以container为起点，k8s既然是容器编排工具，那么一定会有container。
(2)那k8s如何操作这些container呢?从感性的角度来讲，得要有点逼格，k8s不想直接操作 container，因为操作container的事情是docker来做的，k8s中要有自己的最小操作单位，称之为 Pod
说白了，Pod就是一个或多个Container的组合
看看官网怎么描述的 :https://kubernetes.io/docs/concepts/workloads/pods/pod/
A Pod (as in a pod of whales or pea pod) is a group of one or more containers (such as Docker containers),
with shared storage/network, and a specification for how to run the containers.
(3)那Pod的维护谁来做呢?那就是ReplicaSet，通过selector来进行管理
看看官网怎么描述的:https://kubernetes.io/docs/concepts/workloads/controllers/replicaset/
A ReplicaSet is defined with fields, including a selector that specifies how to identify Pods it can acquire, a number of replicas indicating how many Pods it should be maintaining, and a pod template specifying the data of new Pods it should create to meet the number of replicas criteria.
(4)Pod和ReplicaSet的状态如何维护和监测呢?Deployment
官网是如何描述的 :https://kubernetes.io/docs/concepts/workloads/controllers/deployment/
A Deployment controller provides declarative updates for Pods and ReplicaSets.
You describe a desired state in a Deployment, and the Deployment controller changes the actual state to the desired state at a controlled rate. You can define Deployments to create new ReplicaSets, or to remove existing Deployments and adopt all their resources with new Deployments.
(5)不妨把相同或者有关联的Pod分门别类一下，那怎么分门别类呢?
Label（app=login）
官网是如何描述的 :https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/
Labels are key/value pairs that are attached to objects, such as pods.
(6)具有相同label的service要是能够有个名称就好了，Service
An abstract way to expose an application running on a set of Pods as a network service. With Kubernetes you don’t need to modify your application to use an unfamiliar service discovery mechanism. Kubernetes gives Pods their own IP addresses and a single DNS name for a set of Pods, and can load-balance across them.
(7)上述说了这么多，Pod运行在哪里呢?当然是机器咯，比如一台centos机器，我们把这个机器 称作为Node
A node is a worker machine in Kubernetes, previously known as a minion. A node may be a VM or physical machine, depending on the cluster. Each node contains the services necessary to run pods and is managed by the master components.
(8)难道只有一个Node吗?显然不太合适，多台Node共同组成集群才行嘛 画个图表示一下咯，最好能把之前的Label，Service也一起画上去，整体感受一下
(9)此时，我们把目光转移到由3个Node节点组成的Master-Node集群
(10)这个集群要配合完成一些工作，总要有一些组件的支持吧?接下来我们来想想有哪些组件， 然后画一个相对完整的架构图
01-总得要有一个操作集群的客户端，也就是和集群打交道 kubectl 02-请求肯定是到达Master Node，然后再分配给Worker Node创建Pod之的 关键是命令通过kubectl过来之后，是不是要认证授权一下? 03-请求过来之后，Master Node中谁来接收? APIServer 04-API收到请求之后，接下来调用哪个Worker Node创建Pod，Container之类的，得要有调度策略 Scheduler [https://kubernetes.io/docs/concepts/scheduling/kube-scheduler/] 05-Scheduler通过不同的策略，真正要分发请求到不同的Worker Node上创建内容，具体谁负责? Controller Manager 06-Worker Node接收到创建请求之后，具体谁来负责Kubelet服务，最终Kubelet会调用Docker Engine，创建对应的容器 [这边是不是也反应出一 点，在Node上需要有Docker Engine，不然怎么创建维护容器?] 07-会不会涉及到域名解析的问题? DNS 08-是否需要有监控面板能够监测整个集群的状态? Dashboard 09-集群中这些数据如何保存?分布式存储 ETCD 10-至于像容器的持久化存储，网络等可以联系一下Docker中的内容
(11)不妨把这个图翻转一下方便查看
(12)官网K8S架构图
