前言
去年12月份，当Kubernetes社区宣布1.20版本之后会逐步弃用dockershim，当时也有很多自媒体在宣传Kubernetes弃用Docker。其实，我觉得这是一种误导，也许仅仅是为了蹭热度。
dockershim是Kubernetes的一个组件，其作用是为了操作Docker。Docker是在2013年面世的，而Kubernetes是在2016年，所以Docker刚开始并没有想到编排，也不会知道会出现Kubernetes这个庞然大物（它要是知道，也不会败的那么快...）。但是Kubernetes在创建的时候就是以Docker作为容器运行时，很多操作逻辑都是针对的Docker，随着社区越来越健壮，为了兼容更多的容器运行时，才将Docker的相关逻辑独立出来组成了dockershim。
正因为这样，只要Kubernetes的任何变动或者Docker的任何变动，都必须维护dockershim，这样才能保证足够的支持，但是通过dockershim操作Docker，其本质还是操作Docker的底层运行时Containerd，而且Containerd自身也是支持CRI（Container Runtime Interface），那为什么还要绕一层Docker呢？是不是可以直接通过CRI和Containerd进行交互？这也是社区希望启动dockershim的原因之一吧。
那什么是Containerd呢？
Containerd是从Docker中分离的一个项目，旨在为Kubernetes提供容器运行时，负责管理镜像和容器的生命周期。不过Containerd是可以抛开Docker独立工作的。它的特性如下：
- 支持OCI镜像规范，也就是runc
- 支持OCI运行时规范
- 支持镜像的pull
- 支持容器网络管理
- 存储支持多租户
- 支持容器运行时和容器的生命周期管理
- 支持管理网络名称空间
Containerd和Docker在命令使用上的一些区别主要如下：
| 功能 | Docker | Containerd |
| 显示本地镜像列表 | docker images | crictl images |
| 下载镜像 | docker pull | crictl pull |
| 上传镜像 | docker push | 无 |
| 删除本地镜像 | docker rmi | crictl rmi |
| 查看镜像详情 | docker inspect IMAGE-ID | crictl inspecti IMAGE-ID |
| 显示容器列表 | docker ps | crictl ps |
| 创建容器 | docker create | crictl create |
| 启动容器 | docker start | crictl start |
| 停止容器 | docker stop | crictl stop |
| 删除容器 | docker rm | crictl rm |
| 查看容器详情 | docker inspect | crictl inspect |
| attach | docker attach | crictl attach |
| exec | docker exec | crictl exec |
| logs | docker logs | crictl logs |
| stats | docker stats | crictl stats |
可以看到使用方式大同小异。
下面介绍一下使用kubeadm安装K8S集群，并使用containerd作为容器运行时的具体安装步骤。
环境说明
主机节点
| IP地址 | 系统 | 内核 |
| 192.168.0.5 | CentOS7.6 | 3.10 |
| 192.168.0.125 | CentOS7.6 | 3.10 |
软件说明
| 软件 | 版本 |
| kubernetes | 1.20.5 |
| containerd | 1.4.4 |
环境准备
（1）在每个节点上添加 hosts 信息：
$ cat /etc/hosts
192.168.0.5 k8s-master 192.168.0.125 k8s-node01
（2）禁用防火墙：
$ systemctl stop firewalld $ systemctl disable firewalld
（3）禁用SELINUX：
$ setenforce 0 $ cat /etc/selinux/config SELINUX=disabled
（4）创建/etc/sysctl.d/k8s.conf文件，添加如下内容：
net.bridge.bridge-nf-call-ip6tables = 1 net.bridge.bridge-nf-call-iptables = 1 net.ipv4.ip_forward = 1
（5）执行如下命令使修改生效：
$ modprobe br_netfilter $ sysctl -p /etc/sysctl.d/k8s.conf
（6）安装 ipvs
$ cat > /etc/sysconfig/modules/ipvs.modules <<EOF #!/bin/bash modprobe -- ip_vs modprobe -- ip_vs_rr modprobe -- ip_vs_wrr modprobe -- ip_vs_sh modprobe -- nf_conntrack_ipv4 EOF $ chmod 755 /etc/sysconfig/modules/ipvs.modules && bash /etc/sysconfig/modules/ipvs.modules && lsmod | grep -e ip_vs -e nf_conntrack_ipv4
上面脚本创建了的/etc/sysconfig/modules/ipvs.modules文件，保证在节点重启后能自动加载所需模块。使用lsmod | grep -e ip_vs -e nf_conntrack_ipv4命令查看是否已经正确加载所需的内核模块。
（7）安装了 ipset 软件包：
$ yum install ipset -y
为了便于查看 ipvs 的代理规则，最好安装一下管理工具 ipvsadm：
$ yum install ipvsadm -y
（8）同步服务器时间
$ yum install chrony -y $ systemctl enable chronyd $ systemctl start chronyd $ chronyc sources
（9）关闭 swap 分区：
$ swapoff -a
（10）修改/etc/fstab文件，注释掉 SWAP 的自动挂载，使用free -m确认 swap 已经关闭。swappiness 参数调整，修改/etc/sysctl.d/k8s.conf添加下面一行：
vm.swappiness=0
执行sysctl -p /etc/sysctl.d/k8s.conf使修改生效。
（11）接下来可以安装 Containerd
$ yum install -y yum-utils \ device-mapper-persistent-data \ lvm2 $ yum-config-manager \ --add-repo \ https://download.docker.com/linux/centos/docker-ce.repo $ yum list | grep containerd
可以选择安装一个版本，比如我们这里安装最新版本：
$ yum install containerd.io-1.4.4 -y
（12）创建containerd配置文件：
mkdir -p /etc/containerd containerd config default > /etc/containerd/config.toml # 替换配置文件 sed -i "s#k8s.gcr.io#registry.cn-hangzhou.aliyuncs.com/google_containers#g" /etc/containerd/config.toml sed -i '/containerd.runtimes.runc.options/a\ \ \ \ \ \ \ \ \ \ \ \ SystemdCgroup = true' /etc/containerd/config.toml sed -i "s#https://registry-1.docker.io#https://registry.cn-hangzhou.aliyuncs.com#g" /etc/containerd/config.toml
（13）启动Containerd:
systemctl daemon-reload systemctl enable containerd systemctl restart containerd
在确保 Containerd安装完成后，上面的相关环境配置也完成了，现在我们就可以来安装 Kubeadm 了，我们这里是通过指定yum 源的方式来进行安装，使用阿里云的源进行安装：
cat <<EOF > /etc/yum.repos.d/kubernetes.repo [kubernetes] name=Kubernetes baseurl=http://mirrors.aliyun.com/kubernetes/yum/repos/kubernetes-el7-x86_64 enabled=1 gpgcheck=0 repo_gpgcheck=0 gpgkey=http://mirrors.aliyun.com/kubernetes/yum/doc/yum-key.gpg http://mirrors.aliyun.com/kubernetes/yum/doc/rpm-package-key.gpg EOF
然后安装 kubeadm、kubelet、kubectl（我安装的是最新版，有版本要求自己设定版本）：
$ yum install -y kubelet-1.20.5 kubeadm-1.20.5 kubectl-1.20.5
设置运行时：
$ crictl config runtime-endpoint /run/containerd/containerd.sock
可以看到我们这里安装的是 v1.20.5版本，然后将 kubelet 设置成开机启动：
$ systemctl daemon-reload $ systemctl enable kubelet && systemctl start kubelet
“到这里为止上面所有的操作都需要在所有节点执行配置。
”
初始化集群
初始化Master
然后接下来在 master 节点配置 kubeadm 初始化文件，可以通过如下命令导出默认的初始化配置：
$ kubeadm config print init-defaults > kubeadm.yaml
然后根据我们自己的需求修改配置，比如修改 imageRepository 的值，kube-proxy 的模式为 ipvs，需要注意的是由于我们使用的containerd作为运行时，所以在初始化节点的时候需要指定cgroupDriver为systemd【1】
apiVersion: kubeadm.k8s.io/v1beta2 bootstrapTokens: - groups: - system:bootstrappers:kubeadm:default-node-token token: abcdef.0123456789abcdef ttl: 24h0m0s usages: - signing - authentication kind: InitConfiguration localAPIEndpoint: advertiseAddress: 192.168.0.5 bindPort: 6443 nodeRegistration: criSocket: /run/containerd/containerd.sock name: k8s-master taints: - effect: NoSchedule key: node-role.kubernetes.io/master --- apiServer: timeoutForControlPlane: 4m0s apiVersion: kubeadm.k8s.io/v1beta2 certificatesDir: /etc/kubernetes/pki clusterName: kubernetes controllerManager: {} dns: type: CoreDNS etcd: local: dataDir: /var/lib/etcd imageRepository: registry.cn-hangzhou.aliyuncs.com/google_containers kind: ClusterConfiguration kubernetesVersion: v1.20.5 networking: dnsDomain: cluster.local podSubnet: 172.16.0.0/16 serviceSubnet: 10.96.0.0/12 scheduler: {} --- apiVersion: kubeproxy.config.k8s.io/v1alpha1 kind: KubeProxyConfiguration mode: ipvs --- apiVersion: kubelet.config.k8s.io/v1beta1 kind: KubeletConfiguration cgroupDriver: systemd
然后使用上面的配置文件进行初始化：
$ kubeadm init --config=kubeadm.yaml [init] Using Kubernetes version: v1.20.5 [preflight] Running pre-flight checks [preflight] Pulling images required for setting up a Kubernetes cluster [preflight] This might take a minute or two, depending on the speed of your internet connection [preflight] You can also perform this action in beforehand using 'kubeadm config images pull' [certs] Using certificateDir folder "/etc/kubernetes/pki" [certs] Generating "ca" certificate and key [certs] Generating "apiserver" certificate and key [certs] apiserver serving cert is signed for DNS names [k8s-master kubernetes kubernetes.default kubernetes.default.svc kubernetes.default.svc.cluster.local] and IPs [10.96.0.1 192.168.0.5] [certs] Generating "apiserver-kubelet-client" certificate and key [certs] Generating "front-proxy-ca" certificate and key [certs] Generating "front-proxy-client" certificate and key [certs] Generating "etcd/ca" certificate and key [certs] Generating "etcd/server" certificate and key [certs] etcd/server serving cert is signed for DNS names [k8s-master localhost] and IPs [192.168.0.5 127.0.0.1 ::1] [certs] Generating "etcd/peer" certificate and key [certs] etcd/peer serving cert is signed for DNS names [k8s-master localhost] and IPs [192.168.0.5 127.0.0.1 ::1] [certs] Generating "etcd/healthcheck-client" certificate and key [certs] Generating "apiserver-etcd-client" certificate and key [certs] Generating "sa" key and public key [kubeconfig] Using kubeconfig folder "/etc/kubernetes" [kubeconfig] Writing "admin.conf" kubeconfig file [kubeconfig] Writing "kubelet.conf" kubeconfig file [kubeconfig] Writing "controller-manager.conf" kubeconfig file [kubeconfig] Writing "scheduler.conf" kubeconfig file [kubelet-start] Writing kubelet environment file with flags to file "/var/lib/kubelet/kubeadm-flags.env" [kubelet-start] Writing kubelet configuration to file "/var/lib/kubelet/config.yaml" [kubelet-start] Starting the kubelet [control-plane] Using manifest folder "/etc/kubernetes/manifests" [control-plane] Creating static Pod manifest for "kube-apiserver" [control-plane] Creating static Pod manifest for "kube-controller-manager" [control-plane] Creating static Pod manifest for "kube-scheduler" [etcd] Creating static Pod manifest for local etcd in "/etc/kubernetes/manifests" [wait-control-plane] Waiting for the kubelet to boot up the control plane as static Pods from directory "/etc/kubernetes/manifests". This can take up to 4m0s [kubelet-check] Initial timeout of 40s passed. [apiclient] All control plane components are healthy after 70.001862 seconds [upload-config] Storing the configuration used in ConfigMap "kubeadm-config" in the "kube-system" Namespace [kubelet] Creating a ConfigMap "kubelet-config-1.20" in namespace kube-system with the configuration for the kubelets in the cluster [upload-certs] Skipping phase. Please see --upload-certs [mark-control-plane] Marking the node k8s-master as control-plane by adding the labels "node-role.kubernetes.io/master=''" and "node-role.kubernetes.io/control-plane='' (deprecated)" [mark-control-plane] Marking the node k8s-master as control-plane by adding the taints [node-role.kubernetes.io/master:NoSchedule] [bootstrap-token] Using token: abcdef.0123456789abcdef [bootstrap-token] Configuring bootstrap tokens, cluster-info ConfigMap, RBAC Roles [bootstrap-token] configured RBAC rules to allow Node Bootstrap tokens to get nodes [bootstrap-token] configured RBAC rules to allow Node Bootstrap tokens to post CSRs in order for nodes to get long term certificate credentials [bootstrap-token] configured RBAC rules to allow the csrapprover controller automatically approve CSRs from a Node Bootstrap Token [bootstrap-token] configured RBAC rules to allow certificate rotation for all node client certificates in the cluster [bootstrap-token] Creating the "cluster-info" ConfigMap in the "kube-public" namespace [kubelet-finalize] Updating "/etc/kubernetes/kubelet.conf" to point to a rotatable kubelet client certificate and key [addons] Applied essential addon: CoreDNS [addons] Applied essential addon: kube-proxy Your Kubernetes control-plane has initialized successfully! To start using your cluster, you need to run the following as a regular user: mkdir -p $HOME/.kube sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config sudo chown $(id -u):$(id -g) $HOME/.kube/config Alternatively, if you are the root user, you can run: export KUBECONFIG=/etc/kubernetes/admin.conf You should now deploy a pod network to the cluster. Run "kubectl apply -f [podnetwork].yaml" with one of the options listed at: https://kubernetes.io/docs/concepts/cluster-administration/addons/ Then you can join any number of worker nodes by running the following on each as root: kubeadm join 192.168.0.5:6443 --token abcdef.0123456789abcdef \ --discovery-token-ca-cert-hash sha256:446623b965cdb0289c687e74af53f9e9c2063e854a42ee36be9aa249d3f0ccec
拷贝 kubeconfig 文件
$ mkdir -p $HOME/.kube $ sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config $ sudo chown $(id -u):$(id -g) $HOME/.kube/config
添加节点
记住初始化集群上面的配置和操作要提前做好，将 master 节点上面的 $HOME/.kube/config 文件拷贝到 node 节点对应的文件中，安装 kubeadm、kubelet、kubectl，然后执行上面初始化完成后提示的 join 命令即可：
# kubeadm join 192.168.0.5:6443 --token abcdef.0123456789abcdef \ > --discovery-token-ca-cert-hash sha256:446623b965cdb0289c687e74af53f9e9c2063e854a42ee36be9aa249d3f0ccec [preflight] Running pre-flight checks [preflight] Reading configuration from the cluster... [preflight] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -o yaml' [kubelet-start] Writing kubelet configuration to file "/var/lib/kubelet/config.yaml" [kubelet-start] Writing kubelet environment file with flags to file "/var/lib/kubelet/kubeadm-flags.env" [kubelet-start] Starting the kubelet [kubelet-start] Waiting for the kubelet to perform the TLS Bootstrap... This node has joined the cluster: * Certificate signing request was sent to apiserver and a response was received. * The Kubelet was informed of the new secure connection details. Run 'kubectl get nodes' on the control-plane to see this node join the cluster.
“如果忘记了上面的 join 命令可以使用命令kubeadm token create --print-join-command重新获取。
”
执行成功后运行 get nodes 命令：
$ kubectl get no NAME STATUS ROLES AGE VERSION k8s-master NotReady control-plane,master 29m v1.20.5 k8s-node01 NotReady <none> 28m v1.20.5
可以看到是 NotReady 状态，这是因为还没有安装网络插件，接下来安装网络插件，可以在文档 https://kubernetes.io/docs/setup/production-environment/tools/kubeadm/create-cluster-kubeadm/ 中选择我们自己的网络插件，这里我们安装 calio:
$ wget https://docs.projectcalico.org/v3.8/manifests/calico.yaml
# 因为有节点是多网卡，所以需要在资源清单文件中指定内网网卡
$ vi calico.yaml
...... spec: containers: - env: - name: DATASTORE_TYPE value: kubernetes - name: IP_AUTODETECTION_METHOD # DaemonSet中添加该环境变量 value: interface=eth0 # 指定内网网卡 - name: WAIT_FOR_DATASTORE value: "true" - name: CALICO_IPV4POOL_CIDR # 由于在init的时候配置的172网段，所以这里需要修改 value: "172.16.0.0/16" ......
安装calico网络插件
$ kubectl apply -f calico.yaml
隔一会儿查看 Pod 运行状态：
# kubectl get pod -n kube-system NAME READY STATUS RESTARTS AGE calico-kube-controllers-bcc6f659f-zmw8n 0/1 ContainerCreating 0 7m58s calico-node-c4vv7 1/1 Running 0 7m58s calico-node-dtw7g 0/1 PodInitializing 0 7m58s coredns-54d67798b7-mrj2b 1/1 Running 0 46m coredns-54d67798b7-p667d 1/1 Running 0 46m etcd-k8s-master 1/1 Running 0 46m kube-apiserver-k8s-master 1/1 Running 0 46m kube-controller-manager-k8s-master 1/1 Running 0 46m kube-proxy-clf4s 1/1 Running 0 45m kube-proxy-mt7tt 1/1 Running 0 46m kube-scheduler-k8s-master 1/1 Running 0 46m
网络插件运行成功了，node 状态也正常了：
# kubectl get nodes NAME STATUS ROLES AGE VERSION k8s-master Ready control-plane,master 47m v1.20.5 k8s-node01 Ready <none> 46m v1.20.5
用同样的方法添加另外一个节点即可。
配置命令自动补全
yum install -y bash-completion source /usr/share/bash-completion/bash_completion source <(kubectl completion bash) echo "source <(kubectl completion bash)" >> ~/.bashrc
