记得之前使用 Minikube 安装 K8S 的时候，给分3G 内存都嫌小！最近发现一个 K8S 的经量级实现 K3S，最低0.5G 内存就能运行起来，安装方便，和 K8S 用起来区别不大。推荐给大家，希望更多没高端机器的朋友也能够把 K8S 玩起来！

#K3S简介

K3S是一个完全符合Kubernetes的发行版。可以使用单一二进制包安装（不到 100MB），安装简单，内存只有一半，最低0.5G内存就能运行。

为什么叫K3S？开发者希望K3S在内存占用方面只有K8S的一半，Kubernetes是一个10个字母的单词，简写为K8S。那么一半大小就是5个字母的单词，简写为K3S。

#安装

使用官方提供的脚本安装十分方便，一个命令即可完成安装！

  • 使用脚本安装K3S，同时会安装其他实用程序，包括kubectl、crictl、ctr、k3s-killall.sh和k3s-uninstall.sh；
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curl -sfL http://rancher-mirror.cnrancher.com/k3s/k3s-install.sh | INSTALL_K3S_MIRROR=cn sh -
  • 安装完成后提示如下信息，并且会将K3S注册为Linux中的服务；
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Complete!
[INFO]  Creating /usr/local/bin/kubectl symlink to k3s
[INFO]  Creating /usr/local/bin/crictl symlink to k3s
[INFO]  Skipping /usr/local/bin/ctr symlink to k3s, command exists in PATH at /usr/bin/ctr
[INFO]  Creating killall script /usr/local/bin/k3s-killall.sh
[INFO]  Creating uninstall script /usr/local/bin/k3s-uninstall.sh
[INFO]  env: Creating environment file /etc/systemd/system/k3s.service.env
[INFO]  systemd: Creating service file /etc/systemd/system/k3s.service
[INFO]  systemd: Enabling k3s unit
[INFO]  systemd: Starting k3s
  • 可以查看下服务的运行状态，此时显示状态为active。
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[root@linux-local k3s]# systemctl status k3s
● k3s.service - Lightweight Kubernetes
   Loaded: loaded (/etc/systemd/system/k3s.service; enabled; vendor preset: disabled)
   Active: active (running) since Thu 2021-01-28 10:18:39 CST; 2min 0s ago
     Docs: https://k3s.io
  Process: 14983 ExecStartPre=/sbin/modprobe overlay (code=exited, status=0/SUCCESS)
  Process: 14981 ExecStartPre=/sbin/modprobe br_netfilter (code=exited, status=0/SUCCESS)
 Main PID: 14986 (k3s-server)
    Tasks: 71
   Memory: 776.3M

#使用

我们使用kubectl命令操作K3S与之前操作Minikube中的K8S并没有什么区别，这次还是创建一个Nginx的Deployment，然后通过创建Service将其暴露到外部访问。

#创建集群

  • 由于K3S默认安装了kubectl工具，我们可以直接使用它，比如查看kubectl的版本号；
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kubectl version
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Client Version: version.Info{Major:"1", Minor:"20", GitVersion:"v1.20.2+k3s1", GitCommit:"1d4adb0301b9a63ceec8cabb11b309e061f43d5f", GitTreeState:"clean", BuildDate:"2021-01-14T23:52:37Z", GoVersion:"go1.15.5", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"20", GitVersion:"v1.20.2+k3s1", GitCommit:"1d4adb0301b9a63ceec8cabb11b309e061f43d5f", GitTreeState:"clean", BuildDate:"2021-01-14T23:52:37Z", GoVersion:"go1.15.5", Compiler:"gc", Platform:"linux/amd64"}
  • 还可以查看集群详细信息；
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kubectl cluster-info
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Kubernetes control plane is running at https://127.0.0.1:6443
CoreDNS is running at https://127.0.0.1:6443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
Metrics-server is running at https://127.0.0.1:6443/api/v1/namespaces/kube-system/services/https:metrics-server:/proxy
  • 查看集群中的所有Node，可以发现K3S和之前的Minikube一样创建了一个单节点的简单集群。
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kubectl get nodes
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NAME          STATUS   ROLES                  AGE   VERSION
linux-local   Ready    control-plane,master   11m   v1.20.2+k3s1

#部署应用

  • 指定好应用镜像并创建一个Deployment，这里创建一个Nginx应用；
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kubectl create deployment nginx-deployment --image=nginx:1.10
  • 查看所有Deployment；
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kubectl get deployments
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NAME               READY   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment   1/1     1            1           6s

#查看应用

  • 查看Pod的详细状态，包括IP地址、占用端口、使用镜像等信息；
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kubectl describe pods
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Name:         nginx-deployment-597c48c9dd-j49bc
Namespace:    default
Priority:     0
Node:         linux-local/192.168.5.15
Start Time:   Thu, 28 Jan 2021 10:53:14 +0800
Labels:       app=nginx-deployment
              pod-template-hash=597c48c9dd
Annotations:  <none>
Status:       Running
IP:           10.42.0.7
IPs:
  IP:           10.42.0.7
Controlled By:  ReplicaSet/nginx-deployment-597c48c9dd
Containers:
  nginx:
    Container ID:   containerd://560bbeefc9c5714b92ae9d0a1305c2b8746082f4aa11791a2b6e1f4288254ef0
    Image:          nginx:1.10
    Image ID:       docker.io/library/nginx@sha256:6202beb06ea61f44179e02ca965e8e13b961d12640101fca213efbfd145d7575
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Thu, 28 Jan 2021 10:53:16 +0800
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-fnrf7 (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             True 
  ContainersReady   True 
  PodScheduled      True 
Volumes:
  default-token-fnrf7:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-fnrf7
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
                 node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
  Type    Reason     Age   From               Message
  ----    ------     ----  ----               -------
  Normal  Scheduled  38s   default-scheduler  Successfully assigned default/nginx-deployment-597c48c9dd-j49bc to linux-local
  Normal  Pulled     38s   kubelet            Container image "nginx:1.10" already present on machine
  Normal  Created    38s   kubelet            Created container nginx
  Normal  Started    37s   kubelet            Started container nginx
  • 进入容器内部并执行bash命令，如果想退出容器可以使用exit命令。
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kubectl exec -it nginx-deployment-597c48c9dd-j49bc -- bash

#外部访问应用

  • 创建一个Service来暴露nginx-deployment这个Deployment：
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kubectl expose deployment/nginx-deployment --name="nginx-service" --type="NodePort" --port=80
  • 查看所有Service的状态；
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kubectl get services
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NAME            TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)        AGE
kubernetes      ClusterIP   10.43.0.1     <none>        443/TCP        77m
nginx-service   NodePort    10.43.29.39   <none>        80:31494/TCP   10s
  • 在Linux服务器上通过CURL命令即可访问Nginx服务，此时将打印Nginx主页信息；
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curl localhost:31494
  • 相比Minikube在虚拟机中安装容器化应用，K3S直接在本机上安装，直接打开防火墙端口即可在外部访问；
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# 开启端口
firewall-cmd --zone=public --add-port=31494/tcp --permanent
# 重启防火墙
firewall-cmd --reload

#总结

K3S确实是一个很好用的K8S发行版本，不仅安装方便，而且内存占用也降低了。由于直接在本机上安装容器化应用，外部访问也方便了！