【K8S系列】5-K8s实战-Controllers

2023-11-09

K8s控制器

Controllers

官网：https://kubernetes.io/docs/concepts/workloads/controllers/

控制器的作用是用来统一发布Pod的对象，通过yaml文件定义。运行后可以进行查看，变更，删除。

分为三种：

ReplicationController(RC)
ReplicaSet(RS)
Deployment

ReplicationController(RC)

官网：https://kubernetes.io/docs/concepts/workloads/controllers/replicationcontroller/

A ReplicationController ensures that a specified number of pod replicas are running at any one time. In other words, a ReplicationController makes sure that a pod or a homogeneous set of pods is always up and available.

ReplicationController定义了一个期望的场景，即声明某种Pod的副本数量在任意时刻都符合某个预期值，所以RC的定义包含以下几个部分：

Pod期待的副本数（replicas）
用于筛选目标Pod的Label Selector
当Pod的副本数量小于预期数量时，用于创建新Pod的Pod模板（template）

也就是说通过RC实现了集群中Pod的高可用，减少了传统IT环境中手工运维的工作。

Have a try

kind：表示要新建对象的类型

spec.selector：表示需要管理的Pod的label，这里表示包含app: nginx的label的Pod都会被该RC管理

spec.replicas：表示受此RC管理的Pod需要运行的副本数

spec.template：表示用于定义Pod的模板，比如Pod名称、拥有的label以及Pod中运行的应用等

通过改变RC里Pod模板中的镜像版本，可以实现Pod的升级功能

kubectl apply -f nginx-pod.yaml，此时k8s会在所有可用的Node上，创建3个Pod，并且每个Pod都有一个app: nginx的label，同时每个Pod中都运行了一个nginx容器。

如果某个Pod发生问题，Controller Manager能够及时发现，然后根据RC的定义，创建一个新的Pod

扩缩容：kubectl scale rc nginx --replicas=5

(1)创建名为nginx_replication.yaml

apiVersion: v1
kind: ReplicationController
metadata:
  name: nginx
spec:
  replicas: 3
  selector:
    app: nginx
  template:
    metadata:
      name: nginx
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        ports:
        - containerPort: 80

(2)根据nginx_replication.yaml创建pod

kubectl apply -f nginx_replication.yaml

(3)查看pod

kubectl get pods -o wide

   NAME      READY     STATUS
nginx-hksg8   1/1     Running   0          44s   192.168.80.195   w2   
nginx-q7bw5   1/1     Running   0          44s   192.168.190.67   w1  
nginx-zzwzl   1/1     Running   0          44s   192.168.190.68   w1    

kubectl get rc
NAME    DESIRED   CURRENT   READY   AGE
nginx   3         3         3       2m54s

(4)尝试删除一个pod

kubectl delete pods nginx-zzwzl
kubectl get pods

(5)对pod进行扩缩容

kubectl scale rc nginx --replicas=5
kubectl get pods
nginx-8fctt   0/1     ContainerCreating   0          2s
nginx-9pgwk   0/1     ContainerCreating   0          2s
nginx-hksg8   1/1     Running             0          6m50s
nginx-q7bw5   1/1     Running             0          6m50s
nginx-wzqkf   1/1     Running             0          99s

(6)删除pod

kubectl delete -f nginx_replication.yaml
或者
kubectl delete ReplicationController nginx

ReplicaSet(RS)

官网：https://kubernetes.io/docs/concepts/workloads/controllers/replicaset/
A ReplicaSet’s purpose is to maintain a stable set of replica Pods running at any given time. As such, it is often used to guarantee the availability of a specified number of identical Pods.
在Kubernetes v1.2时，RC就升级成了另外一个概念：Replica Set，官方解释为“下一代RC”

ReplicaSet和RC没有本质的区别，kubectl中绝大部分作用于RC的命令同样适用于RS

RS与RC唯一的区别是：RS支持基于集合的Label Selector（Set-based selector），而RC只支持基于等式的Label Selector（equality-based selector），这使得Replica Set的功能更强

尝试一下

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: frontend
  labels:
    app: guestbook
    tier: frontend
spec:
  # modify replicas according to your case
  replicas: 3
  selector:
    matchLabels:
      tier: frontend
  template:
    metadata:
      labels:
        tier: frontend
    spec:
      containers:
      - name: php-redis
        image: gcr.io/google_samples/gb-frontend:v3

注意：一般情况下，我们很少单独使用Replica Set，它主要是被Deployment这个更高的资源对象所使用，从而形成一整套Pod创建、删除、更新的编排机制。当我们使用Deployment时，无须关心它是如何创建和维护Replica Set的，这一切都是自动发生的。同时，无需担心跟其他机制的不兼容问题（比如ReplicaSet不支持rolling-update但Deployment支持）。

Deployment

官网：https://kubernetes.io/docs/concepts/workloads/controllers/deployment/
A Deployment 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.
Deployment相对RC最大的一个升级就是我们可以随时知道当前Pod“部署”的进度。

创建一个Deployment对象来生成对应的Replica Set并完成Pod副本的创建过程

检查Deploymnet的状态来看部署动作是否完成（Pod副本的数量是否达到预期的值）

(1)创建nginx_deployment.yaml文件

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80

(2)根据nginx_deployment.yaml文件创建pod

kubectl apply -f nginx_deployment.yaml

(3)查看pod

kubectl get pods -o wide

kubectl get deployment

kubectl get rs

kubectl get deployment -o wide

nginx-deployment-6dd86d77d-f7dxb   1/1     Running   0      22s   192.168.80.198   w2 
nginx-deployment-6dd86d77d-npqxj   1/1     Running   0      22s   192.168.190.71   w1 
nginx-deployment-6dd86d77d-swt25   1/1     Running   0      22s   192.168.190.70   w1

nginx-deployment[deployment]-6dd86d77d[replicaset]-f7dxb[pod]

(4)当前nginx的版本

kubectl get deployment -o wide

NAME    READY   UP-TO-DATE   AVAILABLE   AGE     CONTAINERS   IMAGES      SELECTOR
nginx-deployment   3/3         3     3  3m27s      nginx    nginx:1.7.9   app=nginx

(5)更新nginx的image版本

kubectl set image deployment nginx-deployment nginx=nginx:1.9.1

(6)删除nginx-deployment

kubectl delete deployment nginx-deployment

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