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大小僅有40MB的k3s為想要節省開銷進行開發和測試的企業提供了一個很好的選擇。本文將用一種極為簡潔的方式，教你在5分鐘之內使用k3s部署輕量Kubernetes集群。
本文來自：Rancher Labs
Kubernetes已經改變了如何大規模部署和管理容器化工作負載。現在開發人員面臨的挑戰主要在于設置過程的復雜性和資源需求量巨大。如果你深受內存不足的困擾，想要部署輕量級Kubernetes集群來減少內存占用，那么你一定要考慮由Rancher Labs發布的輕量級Kubernetes發行版——k3s。它把安裝Kubernetes所需的一切文件都打包進一個40MB大小的二進制文件中，僅需512MB的RAM即可運行。非常適用于資源有限的環境，如邊緣計算場景、IoT等。
在實際場景中，為了獲得開發和測試的動力，節省開銷，用戶希望能夠以最少的資源利用率和較低的硬件規格來部署Kubernetes。而k3s正好滿足了這一需求，它能夠在任何512MB RAM以上的設備上運行集群，如IoT設備或ARM驅動的設備。
既然k3s僅需少量資源即可運行，那么這意味著一些Kubernetes的特性被移除了：
舊的、非默認的、alpha功能
大部分in-tree插件（云提供商和存儲插件），將其用附加組件進行替換
在本文中，我將使用運行在Debian 10上的3個server，每個server有1GB的RAM和1vcpu。其中一個server作為master，其他兩個作為worker節點。
$ openstack server list
+--------------------------------------+-------------------+---------+-----------------------------------+-----------+-----------+
| ID | Name | Status | Networks | Image | Flavor |
+--------------------------------------+-------------------+---------+-----------------------------------+-----------+-----------+
| 4df6a6dc-26e8-4ae0-8b6e-2f97daec0ef3 | k3s-master | ACTIVE | private=10.10.1.159 | Debian-10 | m1.tiny |
| 5ca13239-b745-4f62-ab11-0a27949c9b35 | k3s-node02 | ACTIVE | private=10.10.1.142 | Debian-10 | m1.tiny |
| a54997f2-4d94-4718-86ab-73609b328761 | k3s-node01 | ACTIVE | private=10.10.1.126 | Debian-10 | m1.tiny |
+--------------------------------------+-------------------+---------+-----------------------------------+-----------+-----------+
我將在每個服務器的/ etc / hosts文件中為服務器添加A record。
sudo tee -a /etc/hosts<<EOF
10.10.1.159 k3s-master
10.10.1.126 k3s-node01
10.10.1.142 k3s-node02
EOF
運行k3s的方式有很多，最快的方式是通過提供的bash腳本進行安裝，同時該腳本提供了一個便捷的方式來安裝到systemd或openrc。
curl -sfL https://get.k3s.io | sh -
安裝輸出：
[INFO] Finding latest release
[INFO] Using v0.8.1 as release
[INFO] Downloading hash https://github.com/rancher/k3s/releases/download/v0.8.1/sha256sum-amd64.txt
[INFO] Downloading binary https://github.com/rancher/k3s/releases/download/v0.8.1/k3s
[INFO] Verifying binary download
[INFO] Installing k3s to /usr/local/bin/k3s
[INFO] Creating /usr/local/bin/kubectl symlink to k3s
[INFO] Creating /usr/local/bin/crictl symlink to k3s
[INFO] Creating /usr/local/bin/ctr symlink to k3s
[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
Created symlink /etc/systemd/system/multi-user.target.wants/k3s.service → /etc/systemd/system/k3s.service.
[INFO] systemd: Starting k3s
安裝完成之后，服務會自動啟動。
$ systemctl status k3s
● k3s.service - Lightweight Kubernetes
Loaded: loaded (/etc/systemd/system/k3s.service; enabled; vendor preset: enabled)
Active: active (running) since Tue 2019-09-17 19:20:00 UTC; 2min 24s ago
Docs: https://k3s.io
Process: 833 ExecStartPre=/sbin/modprobe br_netfilter (code=exited, status=0/SUCCESS)
Process: 836 ExecStartPre=/sbin/modprobe overlay (code=exited, status=0/SUCCESS)
Main PID: 837 (k3s-server)
Tasks: 98
Memory: 571.1M
CGroup: /system.slice/k3s.service
├─ 837 /usr/local/bin/k3s server KillMode=process
├─ 851 containerd -c /var/lib/rancher/k3s/agent/etc/containerd/config.toml -a /run/k3s/containerd/containerd.sock --state /run/k3s/conta
├─1110 containerd-shim -namespace k8s.io -workdir /var/lib/rancher/k3s/agent/containerd/io.containerd.runtime.v1.linux/k8s.io/f6eeb59978
├─1127 /pause
├─1207 containerd-shim -namespace k8s.io -workdir /var/lib/rancher/k3s/agent/containerd/io.containerd.runtime.v1.linux/k8s.io/0baf0ca181
├─1225 /coredns -conf /etc/coredns/Corefile
├─1576 containerd-shim -namespace k8s.io -workdir /var/lib/rancher/k3s/agent/containerd/io.containerd.runtime.v1.linux/k8s.io/dcce4b7e17
├─1594 /pause
├─1599 containerd-shim -namespace k8s.io -workdir /var/lib/rancher/k3s/agent/containerd/io.containerd.runtime.v1.linux/k8s.io/50816ffba8
├─1617 /pause
├─1824 containerd-shim -namespace k8s.io -workdir /var/lib/rancher/k3s/agent/containerd/io.containerd.runtime.v1.linux/k8s.io/d0ff393609
├─1842 /bin/sh /usr/bin/entry
├─1882 containerd-shim -namespace k8s.io -workdir /var/lib/rancher/k3s/agent/containerd/io.containerd.runtime.v1.linux/k8s.io/046779175f
├─1899 /bin/sh /usr/bin/entry
├─1904 containerd-shim -namespace k8s.io -workdir /var/lib/rancher/k3s/agent/containerd/io.containerd.runtime.v1.linux/k8s.io/93f0fe2361
└─1921 /traefik --configfile=/config/traefik.toml
Sep 17 19:20:34 deb10 k3s[837]: E0917 19:20:34.714229 837 daemon_controller.go:302] kube-system/svclb-traefik failed with : error storing statu
Sep 17 19:20:34 deb10 k3s[837]: E0917 19:20:34.719452 837 daemon_controller.go:302] kube-system/svclb-traefik failed with : error storing statu
Sep 17 19:20:34 deb10 k3s[837]: I0917 19:20:34.726816 837 reconciler.go:207] operationExecutor.VerifyControllerAttachedVolume started for volum
Sep 17 19:20:34 deb10 k3s[837]: I0917 19:20:34.726836 837 reconciler.go:207] operationExecutor.VerifyControllerAttachedVolume started for volum
Sep 17 19:20:34 deb10 k3s[837]: I0917 19:20:34.726857 837 reconciler.go:207] operationExecutor.VerifyControllerAttachedVolume started for volum
Sep 17 19:20:34 deb10 k3s[837]: I0917 19:20:34.726869 837 reconciler.go:207] operationExecutor.VerifyControllerAttachedVolume started for volum
Sep 17 19:20:35 deb10 k3s[837]: I0917 19:20:35.529102 837 reconciler.go:181] operationExecutor.UnmountVolume started for volume "helm-traefik-t
Sep 17 19:20:35 deb10 k3s[837]: I0917 19:20:35.542858 837 operation_generator.go:799] UnmountVolume.TearDown succeeded for volume "kubernetes.i
Sep 17 19:20:35 deb10 k3s[837]: I0917 19:20:35.629277 837 reconciler.go:285] Volume detached for volume "helm-traefik-token-kjwrl" (UniqueName:
Sep 17 19:20:36 deb10 k3s[837]: W0917 19:20:36.355273 837 pod_container_deletor.go:75] Container "2f0c4a787b13c029d65aa865c1b473f5a7497cb6f9b92
將kubeconfig文件寫入/etc/rancher/k3s/k3s.yaml：
$ cat /etc/rancher/k3s/k3s.yaml
cat: /etc/rancher/k3s/k3s.yaml: Permission denied
debian@deb10:~$ sudo cat /etc/rancher/k3s/k3s.yaml
apiVersion: v1
clusters:
- cluster:
certificate-authority-data: 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
server: https://localhost:6443
name: default
contexts:
- context:
cluster: default
user: default
name: default
current-context: default
kind: Config
preferences: {}
users:
- name: default
user:
password: 2d99cae31c075743be704bb717ceaae8
username: admin
其他已經安裝的有：
kubectl
crictl
k3s-killall.sh
要在Woker節點上安裝k3s，我們應該將K3S_URL以及K3S_TOKEN或K3S_CLUSTER_SECRET環境變量一起傳遞。
K3S_TOKEN在第一個節點上的/ var / lib / rancher / k3s / server / node-token中創建。
$ sudo cat /var/lib/rancher/k3s/server/node-token
K1042e2f8e353b9409472c1e0cca8457abe184dc7be3f0805109e92c50c193ceb42::node:c83acbf89a7de7026d6f6928dc270028
所以為了在worker節點上安裝Kubernetes，我將運行：
k3s_url="https://k3s-master:6443"
k3s_token="K1042e2f8e353b9409472c1e0cca8457abe184dc7be3f0805109e92c50c193ceb42::node:c83acbf89a7de7026d6f6928dc270028"
curl -sfL https://get.k3s.io | K3S_URL=${k3s_url} K3S_TOKEN=${k3s_token} sh -
安裝輸出：
[INFO] Finding latest release
[INFO] Using v0.8.1 as release
[INFO] Downloading hash https://github.com/rancher/k3s/releases/download/v0.8.1/sha256sum-amd64.txt
[INFO] Downloading binary https://github.com/rancher/k3s/releases/download/v0.8.1/k3s
[INFO] Verifying binary download
[INFO] Installing k3s to /usr/local/bin/k3s
[INFO] Creating /usr/local/bin/kubectl symlink to k3s
[INFO] Creating /usr/local/bin/crictl symlink to k3s
[INFO] Creating /usr/local/bin/ctr symlink to k3s
[INFO] Creating killall script /usr/local/bin/k3s-killall.sh
[INFO] Creating uninstall script /usr/local/bin/k3s-agent-uninstall.sh
[INFO] env: Creating environment file /etc/systemd/system/k3s-agent.service.env
[INFO] systemd: Creating service file /etc/systemd/system/k3s-agent.service
[INFO] systemd: Enabling k3s-agent unit
Created symlink /etc/systemd/system/multi-user.target.wants/k3s-agent.service → /etc/systemd/system/k3s-agent.service.
[INFO] systemd: Starting k3s-agent
登錄到其中一個master節點并檢查集群狀態：
$ sudo kubectl config get-clusters
NAME
default
$ sudo kubectl cluster-info
Kubernetes master is running at https://localhost:6443
CoreDNS is running at https://localhost:6443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
$ sudo kubectl get nodes
NAME STATUS ROLES AGE VERSION
k3s-master Ready master 14m v1.14.6-k3s.1
k3s-node01 Ready worker 3m11s v1.14.6-k3s.1
k3s-node02 Ready worker 3m58s v1.14.6-k3s.1
$ sudo kubectl get namespaces
NAME STATUS AGE
default Active 16m
kube-node-lease Active 16m
kube-public Active 16m
kube-system Active 16m
$ sudo kubectl get endpoints -n kube-system
NAME ENDPOINTS AGE
kube-dns 10.42.0.2:53,10.42.0.2:53,10.42.0.2:9153 14m
traefik 10.42.0.5:80,10.42.0.5:443 14m
$ sudo kubectl get pods -n kube-system
NAME READY STATUS RESTARTS AGE
coredns-b7464766c-q9frk 1/1 Running 0 15m
helm-install-traefik-8dhpk 0/1 Completed 0 15m
svclb-traefik-9c2j8 2/2 Running 0 4m49s
svclb-traefik-bf9zd 2/2 Running 0 4m2s
svclb-traefik-v2fpx 2/2 Running 0 14m
traefik-5c79b789c5-k589d 1/1 Running 0 14m
使用crictl命令來查看正在運行的容器
# Master
$ sudo crictl ps
CONTAINER ID IMAGE CREATED STATE NAME ATTEMPT POD ID
acfafb50852d3 18471c10e6e4b 16 minutes ago Running traefik 0 bf8534452389f
fee5ac7e88f2e 4a065d8dfa588 16 minutes ago Running lb-port-443 0 e7068ff7ab2f2
bbab5b07e5efb 4a065d8dfa588 16 minutes ago Running lb-port-80 0 e7068ff7ab2f2
65c5d1333ea04 2ee68ed074c6e 16 minutes ago Running coredns 0 435c51f4716fc
# Workers
$ sudo crictl ps
CONTAINER ID IMAGE CREATED STATE NAME ATTEMPT POD ID
7ad5c83d6466f 4a065d8dfa588 6 minutes ago Running lb-port-443 0 bf8d9fe57c3f3
c1380eabc0b33 4a065d8dfa588 6 minutes ago Running lb-port-80 0 bf8d9fe57c3f3
大功告成啦！如果你需要更高級的配置，請參閱k3s文檔：
https://rancher.com/docs/k3s/latest/en/
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