理解K8s中的三个IP概念
对于K8s集群中出现的三个IP概念：Node IP、Pod IP以及Cluster IP，它们分别指向不同的含义：
- 多个Pod部署在同一个物理机节点(或者虚拟机节点)上，此时这个节点的IP就是
Node IP。 - 由多个pod组成的部署管理对象
Deployment，如果需要对外提供访问能力，就必须借助Service, 而service对象本身的IP就是Cluster IP。集群外如果要访问service，就必须通过Cluster IP访问。 - 每个Pod管理一个或多个容器，Pod本身也有自己的虚拟IP，即
Pop IP。
»如何访问Pod中的服务
假设一个nginx集群的部署如下：
[dockerg@VM-24-6-centos root]$ kubectl get pods
NAME READY STATUS RESTARTS AGE
nginx-6799fc88d8-w7994 1/1 Running 0 120m
nginx-6799fc88d8-xn4d9 1/1 Running 0 4h29m
nginx-6799fc88d8-zt2bs 1/1 Running 0 4h23m
[dockerg@VM-24-6-centos root]$ kubectl get deployment
NAME READY UP-TO-DATE AVAILABLE AGE
nginx 3/3 3 3 4h29m
[dockerg@VM-24-6-centos root]$ kubectl get service
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 5h51m
nginx NodePort 10.104.80.47 <none> 80:30983/TCP 14s如果需要调试其中的某一个特定的pod上的服务，这个时候，应该屏蔽其负载均衡的功能，因此，可以采用kube-proxy的方式对指定pod设置一个路由出来：
[dockerg@VM-24-6-centos root]$ kubectl port-forward nginx-6799fc88d8-w7994 12223:80
Forwarding from 127.0.0.1:12223 -> 80
Forwarding from [::1]:12223 -> 80
Handling connection for 12223
# 启动另外一个terminel
[dockerg@VM-24-6-centos root]$ curl -XGET http://127.0.0.1:12223
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>
<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>
<p><em>Thank you for using nginx.</em></p>
</body>
</html>对于NodePort方式，一个定义好的Service，它有自己的ClusterIP以及端口port，它相当于一个集群的负载均衡入口,由clusterIP:clusterPort转发到podIp:podPort，但是cluster-ip只能由集群内部访问，当需要集群外部访问时，则需要采用NodePort方式，顾名思义，就是在物理节点Node上开一个端口，并由它转发到Service的Cluster-IP和Port上。
以上归类了访问服务的四种不同的方式。
Kube-proxy一般用于调试，直接将某个pod的某个端口映射到当前主机的某个pod上。Cluster-IP提供集群内部的服务发现和负载均衡，但只局限于集群内部访问，如组成集群的多个Pod上的容器。NodePort即加一层从主机端口到集群端口的映射，支持从集群外部访问服务。Ingress相当于一个前置的LB网关，支持七层转发。
»Pod的管理
对于Pod的管理，基本上可以由下列这些命令来完成：
创建Deployment，即在Deployment中创建pod副本：
[dockerg@VM-24-6-centos root]$ kubectl create deployment nginx --image=nginx --replicas=2 deployment.apps/nginx
deployment.apps/nginx created查看pods:
[dockerg@VM-24-6-centos root]$ kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-6799fc88d8-g4xvh 1/1 Running 0 2m29s 172.17.0.3 minikube <none> <none>
nginx-6799fc88d8-xn4d9 1/1 Running 0 2m29s 172.17.0.6 minikube <none> <none>查看pod的详细描述：
[dockerg@VM-24-6-centos root]$ kubectl describe pod nginx
Name: nginx-6799fc88d8-g4xvh
Namespace: default
Priority: 0
Node: minikube/192.168.49.2
Start Time: Fri, 12 Nov 2021 11:52:37 +0800
Labels: app=nginx
pod-template-hash=6799fc88d8
Annotations: <none>
Status: Running
IP: 172.17.0.3
IPs:
IP: 172.17.0.3
Controlled By: ReplicaSet/nginx-6799fc88d8
Containers:
nginx:
Container ID: docker://6d4c63a630ebd345d28f3fb5a7b41ccf849851d0231936d8be0331242bdd512a
Image: nginx
Image ID: docker-pullable://nginx@sha256:dfef797ddddfc01645503cef9036369f03ae920cac82d344d58b637ee861fda1
Port: <none>
Host Port: <none>
State: Running
Started: Fri, 12 Nov 2021 11:52:40 +0800
Ready: True
Restart Count: 0
Environment: <none>
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-n4c9b (ro)
Conditions:
...伸缩容，修改Pod的副本数：
[dockerg@VM-24-6-centos root]$ kubectl patch deployment nginx -p '{"spec":{"replicas":3}}' -n default
deployment.apps/nginx patched
[dockerg@VM-24-6-centos root]$ kubectl get pods
NAME READY STATUS RESTARTS AGE
nginx-6799fc88d8-g4xvh 1/1 Running 0 6m23s
nginx-6799fc88d8-xn4d9 1/1 Running 0 6m23s
nginx-6799fc88d8-zt2bs 1/1 Running 0 22s删除pod：
kubectl delete deployment nginx通过配置文件创建，同时指定多个容器：
kubectl create -f ./nginx.yaml
apiVersion: v1
kind: Pod
metadata:
name: nginx
labels:
app: nginx
spec:
containers:
- name: n1
image: nginx
ports:
- containerPort: 80
- name: n2
image: nginx
ports:
- containerPort: 81