Kubernetes指南: 从零开始搭建集群

在云计算时代，容器化已经成为了一种广泛使用的技术，Kubernetes是其中的佼佼者，其作为一个容器编排平台，在管理上的优势及其高可用性、易扩展性深受企业和开发者的喜爱。在本文章中，我们将从零开始搭建Kubernetes集群，并解释其中的技术知识点。

1. 环境准备

在开始之前，需要先确定好环境，Kubernetes分为Master节点和Worker节点，其中Master节点需要至少2个，Worker节点至少1个，硬件环境和软件环境需要满足一定的要求。硬件环境建议：

- Master节点：CPU 2核，内存 2GB，硬盘 40GB以上
- Worker节点：CPU 4核，内存 4GB，硬盘 40GB以上

软件环境建议：

- 操作系统：CentOS7.4以上
- Docker：18.09.0以上
- Kubeadm：1.20.1及以上

2. 安装Docker

在CentOS系统下，我们可以执行下方脚本安装Docker：

```bash
$ sudo yum install -y yum-utils device-mapper-persistent-data lvm2
$ sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
$ sudo yum install -y docker-ce-18.09.0 docker-ce-cli-18.09.0 containerd.io
$ sudo systemctl start docker
$ sudo systemctl enable docker
```

3. 安装Kubeadm

我们可以执行如下脚本安装Kubeadm：

```bash
$ sudo vi /etc/sysctl.d/k8s.conf 
# 写入如下内容
net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1

$ sudo sysctl --system
$ sudo setenforce 0
$ sudo sed -i 's/SELINUX=enforcing/SELINUX=permissive/' /etc/selinux/config 

$ sudo vi /etc/yum.repos.d/kubernetes.repo
# 写入如下内容
[kubernetes]
name=Kubernetes
baseurl=https://mirrors.aliyun.com/kubernetes/yum/repos/kubernetes-el7-x86_64/
enabled=1
gpgcheck=0
repo_gpgcheck=0
gpgkey=https://mirrors.aliyun.com/kubernetes/yum/doc/yum-key.gpg https://mirrors.aliyun.com/kubernetes/yum/doc/rpm-package-key.gpg

$ sudo yum install -y kubelet-1.20.1 kubeadm-1.20.1 kubectl-1.20.1 --disableexcludes=kubernetes
$ sudo systemctl enable kubelet
$ sudo systemctl start kubelet
```

4. 搭建Master节点

在搭建Master节点时，我们需要先确定好IP地址，并编辑好如下配置文件：

```yaml
apiVersion: kubeadm.k8s.io/v1beta2
kind: ClusterConfiguration

kubernetesVersion: stable

apiServer:
  certSANs:
  - "{{ Master节点IP地址 }}"
  controlPlaneEndpoint: "{{ Master节点IP地址 }}:6443"
  extraArgs:
    audit-log-path: /var/log/kubernetes/audit.log
    audit-log-maxage: "30"
    audit-log-maxbackup: "3"
    audit-log-maxsize: "100"
    authorization-mode: Node,RBAC
    enable-admission-plugins: NamespaceLifecycle,LimitRanger,ServiceAccount,DefaultStorageClass,ResourceQuota
    runtime-config: api/all=true
    service-node-port-range: 30000-32767

controllerManager:
  extraArgs:
    node-cidr-mask-size: "24"
    node-monitor-grace-period: "30s"
    pod-eviction-timeout: "2m"
    use-service-account-credentials: "true"

networking:
  dnsDomain: cluster.local
  podSubnet: "10.244.0.0/16"
  serviceSubnet: "10.96.0.0/12"
```

然后，我们在Master节点上执行如下脚本：

```bash
$ sudo kubeadm init --config kubeadm-config.yaml
```

在执行完成后，我们可以看到如下输出：

```bash
[init] Using Kubernetes version: v1.20.0
[preflight] Running pre-flight checks
    [WARNING FileExisting-crictl]: crictl not found in system path
[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'
[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
[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 [master-1 kubernetes kubernetes.default kubernetes.default.svc kubernetes.default.svc.cluster.local] and IPs [10.96.0.1 192.168.1.120]
[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 [localhost] and IPs [192.168.1.120 127.0.0.1 ::1]
[certs] Generating "etcd/peer" certificate and key
[certs] etcd/peer serving cert is signed for DNS names [localhost] and IPs [192.168.1.120 127.0.0.1 ::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
[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 80.001069 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
[kubelet-start] Restarting the kubelet to use the new kubelet configuration
[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
[csr-approver] CSR approval is disabled. Nodes that match this CSR will be not be permitted to join the cluster. Passing --apiserver-advertise-address=0.0.0.0 may allow unauthorized nodes to join the cluster.
[bootstrap-token] configured RBAC rules to allow certificate rotation for all node client certificates in the cluster
[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 {{ Master节点IP地址 }}:6443 --token {{ Token }} \
        --discovery-token-ca-cert-hash sha256:{{ CA证书哈希值 }}
```

在执行完成后，我们需要执行如下脚本，让普通用户也拥有使用Kubernetes的权限：

```bash
$ mkdir -p $HOME/.kube
$ sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
$ sudo chown $(id -u):$(id -g) $HOME/.kube/config
```

5. 搭建Worker节点

在搭建Worker节点时，我们需要使用之前Master节点输出的join命令，并将其执行在Worker节点上，如下：

```bash
$ sudo kubeadm join {{ Master节点IP地址 }}:6443 --token {{ Token }} \
        --discovery-token-ca-cert-hash sha256:{{ CA证书哈希值 }}
```

执行成功后，在Master节点上执行如下脚本：

```bash
$ kubectl get nodes
```

如果输出了刚刚加入的Worker节点信息，说明Worker节点已经成功加入到了集群中。

至此，我们已经成功搭建了一个Kubernetes集群，并且已经加入了一个Worker节点。在实际生产环境中，我们还需要进行更多的配置和优化，例如网络、存储、高可用性等方面，这将在后续的文章中进行探讨。