【Kubernetes 003】Centos7通过Kubeadm安装Kubernetes1.15详解（附一键安装脚本）

kubeadm是Kubernetes官方提供的用于快速安装Kubernetes集群的工具，比起复杂繁琐的源码安装要方便快捷很多。这一章我们就通过kubeadm搭建起一个Kubernetes集群。为后面的学习做准备。

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一键安装脚本

为了方便重复安装，我将本节中一直到flannel部分的步骤制作成了一键安装脚本，分为master部分和node部分。

master: https://github.com/Victor2Code/centos-k8s-init/blob/master/centos_7-k8s_v1_15-init-master.sh
node: https://github.com/Victor2Code/centos-k8s-init/blob/master/centos_7-k8s_v1_15-init-node.sh

有兴趣的朋友可以对照着本文理解和使用一键安装脚本。

准备

在正式用kubeadm安装之前，有一些准备条件先要做好

系统准备

准备了两台全新的centos7机器如下，按照本文章中方法请先确保所有机器都可以科学上网

172.29.56.175 k8s-master
172.29.56.176 k8s-node1

其中每台机器的规格为

• CPU 4
• RAM 4G
• Disk 100G

确保所有机器的hosts文件都同步

cat >> /etc/hosts << EOF
172.29.56.175 k8s-master
172.29.56.176 k8s-node1
EOF

后续如果有新的机器加入集群可以考虑用saltstack之类的工具批量修改文件

关掉系统自带的firewalld防火墙服务而改为iptables

sudo systemctl stop firewalld.service
sudo systemctl disable firewalld.service
sudo yum -y install iptables-services
sudo systemctl start iptables.service
sudo systemctl enable iptables.service

开放官方文档中列出的组件所需要的端口

iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT
iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 443 -j ACCEPT
iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 6443 -j ACCEPT
iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 2379:2380 -j ACCEPT
iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 10250:10252 -j ACCEPT
iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 30000:32767 -j ACCEPT

根据机器局域网环境开放局域网ip段，并将上述规则保存至配置文件

iptables -I INPUT -d 172.29.0.0/16 -j ACCEPT
iptables -I INPUT -s 172.29.0.0/16 -j ACCEPT
service iptables save

之后跑iptables -nvL确认一下iptables filter表中FOWARD链的默认策略(pllicy)为ACCEPT。

这里补充下一个比较坑的点，后来在安装完了flannel以后，coreDNS一直报错，根据网上的建议发现是防火墙的原因

将默认的拒绝FORWARD包的规则注释掉，重启生效

sed -i '/-A FORWARD -j REJECT/s/^/#/g' /etc/sysconfig/iptables
sudo systemctl restart iptables

禁用Selinux

setenforce 0
sudo sed -i 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/selinux/config

修改内核参数

cat > /etc/sysctl.d/k8s.conf << EOF
net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1
net.ipv4.ip_forward = 1
EOF
modprobe br_netfilter
sysctl -p /etc/sysctl.d/k8s.conf

开启ipvs所需模块

kube-proxy可以开启ipvs模式或者iptables模式，因为效率更高所以采用ipvs模式，如果下面这些模块没加载成功即使配置开启了ipvs模式也会回退到iptables模式。

加载5个所需模块并设置为机器重启也能自动加载

cat > /etc/sysconfig/modules/ipvs.modules <

安装ipvs管理工具ipvsadm以及ipset

sudo yum -y install ipvsadm
sudo yum -y install ipset

安装Docker

Docker目前仍然是Kubernetes默认的容器运行接口，也就是CRI(Container Runtime Interface)，所以要安装Docker。

安装Docker的yum源

yum install -y yum-utils device-mapper-persistent-data lvm2
yum-config-manager \
    --add-repo \
    https://download.docker.com/linux/centos/docker-ce.repo

查看一下可安装的docker版本

yum list docker-ce.x86_64  --showduplicates |sort -r

Kubernetes 1.15当前支持的docker版本列表是1.13.1, 17.03, 17.06, 17.09, 18.06, 18.09。 这里在各节点安装docker的18.09.9版本。

yum makecache fast

yum install -y --setopt=obsoletes=0 \
  docker-ce-18.09.9-3.el7

systemctl start docker
systemctl enable docker

根据文档CRI installation中的内容，对于使用systemd作为init system的Linux的发行版，使用systemd作为docker的cgroup driver可以确保服务器节点在资源紧张的情况更加稳定，因此这里修改各个节点上docker的cgroup driver为systemd

cat > /etc/docker/daemon.json <

使用kubeadm部署Kubernetes

准备工作做好，下面就要正式开始部署了。

安装kubeadm和kubelet

对所有节点做如下操作。

配置yum源

cat < /etc/yum.repos.d/kubernetes.repo
[kubernetes]
name=Kubernetes
baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
enabled=1
gpgcheck=1
repo_gpgcheck=1
gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg
        https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
EOF

因为是从Google云上下载，可以先curl https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64看下是否可用，如果不可用需要科学上网

安装之前同样也可以查看一下所有可供安装的版本

yum list kubelet --showduplicates

最新版本是1.18，不过我们还是安装1.15版本

yum makecache fast
yum install kubeadm-1.15.11-0 kubelet-1.15.11-0 kubectl-1.15.11-0

成功安装的显示如下

Installed:
  kubeadm.x86_64 0:1.15.11-0                      kubectl.x86_64 0:1.15.11-0                      kubelet.x86_64 0:1.15.11-0                    

Dependency Installed:
  conntrack-tools.x86_64 0:1.4.4-5.el7_7.2        cri-tools.x86_64 0:1.13.0-0                     kubernetes-cni.x86_64 0:0.7.5-0          
  libnetfilter_cthelper.x86_64 0:1.0.0-10.el7_7.1 libnetfilter_cttimeout.x86_64 0:1.0.0-6.el7_7.1 libnetfilter_queue.x86_64 0:1.0.2-2.el7_2
  socat.x86_64 0:1.7.3.2-2.el7

运行kubelet –help可以看到原来kubelet的绝大多数命令行flag参数都被DEPRECATED了，如：

--address 0.0.0.0 The IP address for the Kubelet to serve on (set to 0.0.0.0 for all IPv4 interfaces and `::` for all IPv6 interfaces) (default 0.0.0.0) (DEPRECATED: This parameter should be set via the config file specified by the Kubelet's --config flag. See https://kubernetes.io/docs/tasks/administer-cluster/kubelet-config-file/ for more information.)

而官方推荐我们使用本地配置文件去对kubelet进行设置，具体可以参考Set Kubelet parameters via a config file，待会在下面的安装过程中我们就会看到这个配置文件。kubelet的配置文件必须是json或yaml格式。

关闭swap

swapoff -a
sed -i '/swap/s/^/#/g' /etc/fstab
cat >> /etc/sysctl.d/k8s.conf << EOF
vm.swappiness=0
EOF
sysctl -p /etc/sysctl.d/k8s.conf

运行free -m发现都是0表示swap已经被关闭

使用kubeadm init初始化集群

对所有节点做如下操作。

开机启动kubelet

systemctl enable kubelet.service

对k8s-master节点做如下操作。

创建初始化集群所需的配置文件kubeadm.yaml。不过在此之前可以先通过kubeadm config print init-defaults来查看一下默认的初始化配置参数

[root@k8s-master yum.repos.d]# kubeadm config print init-defaults
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: 1.2.3.4
  bindPort: 6443
nodeRegistration:
  criSocket: /var/run/dockershim.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: k8s.gcr.io
kind: ClusterConfiguration
kubernetesVersion: v1.15.0
networking:
  dnsDomain: cluster.local
  serviceSubnet: 10.96.0.0/12
scheduler: {}

• 这里的effect: NoSchedule会在master上打一个污点，不让master接受任务调度，如果想让master也接受调度可以改为effect: PreferNoSchedule
• 这里的advertiseAddress: 1.2.3.4需要修改为master的物理网卡IP
• 因为后面会安装flannel，需要添加podSubnet: 10.244.0.0/16

于是自定义配置文件如下

cat > /root/k8s-install/kubeadm.yaml << EOF
apiVersion: kubeadm.k8s.io/v1beta2
kind: InitConfiguration
localAPIEndpoint:
  advertiseAddress: 172.29.56.175
  bindPort: 6443
nodeRegistration:
  taints:
  - effect: PreferNoSchedule
    key: node-role.kubernetes.io/master
---
apiVersion: kubeadm.k8s.io/v1beta2
kind: ClusterConfiguration
kubernetesVersion: v1.15.0
networking:
  podSubnet: 10.244.0.0/16
EOF

下面开始在master上进行集群初始化，并保存log，因为这个log里面有加入node节点的命令

kubeadm init --config /root/k8s-install/kubeadm.yaml | tee /root/k8s-install/init-log.log

初始化的log如下

[init] Using Kubernetes version: v1.15.0
[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'
[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] Activating the kubelet service
[certs] Using certificateDir folder "/etc/kubernetes/pki"
[certs] Generating "etcd/ca" certificate and key
[certs] Generating "apiserver-etcd-client" certificate and key
[certs] Generating "etcd/healthcheck-client" 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 [172.29.56.175 127.0.0.1 ::1]
[certs] Generating "etcd/peer" certificate and key
[certs] etcd/peer serving cert is signed for DNS names [k8s-master localhost] and IPs [172.29.56.175 127.0.0.1 ::1]
[certs] Generating "front-proxy-ca" certificate and key
[certs] Generating "front-proxy-client" certificate and key
[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 [10.96.0.1 172.29.56.175]
[certs] Generating "apiserver-kubelet-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
[apiclient] All control plane components are healthy after 35.503997 seconds
[upload-config] Storing the configuration used in ConfigMap "kubeadm-config" in the "kube-system" Namespace
[kubelet] Creating a ConfigMap "kubelet-config-1.15" 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 label "node-role.kubernetes.io/master=''"
[mark-control-plane] Marking the node k8s-master as control-plane by adding the taints [node-role.kubernetes.io/master:PreferNoSchedule]
[bootstrap-token] Using token: 085q2m.0dp7oldsibne4tv4
[bootstrap-token] Configuring bootstrap tokens, cluster-info ConfigMap, RBAC Roles
[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
[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

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 172.29.56.175:6443 --token 085q2m.0dp7oldsibne4tv4 \
    --discovery-token-ca-cert-hash sha256:611c726b02601f18cec16a9aec8ef985d1236557b59029e56fd8e6d43fe04c81

可以看出初始化一个kubernetes集群大概有如下几个步骤

• [kubelet-start] 生成kubelet的配置文件”/var/lib/kubelet/config.yaml”
• [certs]生成相关的各种证书
• [kubeconfig]生成相关的kubeconfig文件
• [control-plane]使用/etc/kubernetes/manifests目录中的yaml文件创建apiserver、controller-manager、scheduler的静态pod
• [bootstraptoken]生成token记录下来，后边使用kubeadm join往集群中添加节点时会用到
• 然后是给常规用户kubectl访问权限的配置方式

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

• 下一步应该安装网络插件了，也就是我们之前提到的flannel，构建扁平网络
• 最后给出了安装完网络插件后将节点加入集群的命令

kubeadm join 172.29.56.175:6443 --token 085q2m.0dp7oldsibne4tv4 \
    --discovery-token-ca-cert-hash sha256:611c726b02601f18cec16a9aec8ef985d1236557b59029e56fd8e6d43fe04c81

在master上执行完上面给出的三条命令后，查看一下集群状态，确认个组件都处于healthy状态

[root@k8s-master ~]# kubectl get cs
NAME                 STATUS    MESSAGE             ERROR
controller-manager   Healthy   ok                  
scheduler            Healthy   ok                  
etcd-0               Healthy   {"health":"true"}

安装flannel

flannel必须通过yaml配置文件来安装，将该文件和之前的一些重要文件放在一起

cd /root/k8s-install/
curl -O https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml

如果机器有多个网卡，还需要在yml文件中用iface来指定内网网卡，而如果只有一个内网网卡则不必指定

containers:
      - name: kube-flannel
        image: quay.io/coreos/flannel:v0.11.0-amd64
        command:
        - /opt/bin/flanneld
        args:
        - --ip-masq
        - --kube-subnet-mgr
        - --iface=eth1
......

然后根据配置文件进行安装

kubectl apply -f  kube-flannel.yml

结果如下

podsecuritypolicy.policy/psp.flannel.unprivileged created
clusterrole.rbac.authorization.k8s.io/flannel created
clusterrolebinding.rbac.authorization.k8s.io/flannel created
serviceaccount/flannel created
configmap/kube-flannel-cfg created
daemonset.apps/kube-flannel-ds-amd64 created
daemonset.apps/kube-flannel-ds-arm64 created
daemonset.apps/kube-flannel-ds-arm created
daemonset.apps/kube-flannel-ds-ppc64le created
daemonset.apps/kube-flannel-ds-s390x created

使用kubectl get pod --all-namespaces -o wide确保所有的Pod都处于Running状态

[root@k8s-master k8s-install]# kubectl get pod --all-namespaces -o wide
NAMESPACE     NAME                                 READY   STATUS    RESTARTS   AGE     IP              NODE         NOMINATED NODE   READINESS GATES
kube-system   coredns-5d4dd4b4db-78x58             1/1     Running   0          31m     10.244.0.3      k8s-master              
kube-system   coredns-5d4dd4b4db-m88wx             1/1     Running   0          31m     10.244.0.2      k8s-master              
kube-system   etcd-k8s-master                      1/1     Running   0          30m     172.29.56.175   k8s-master              
kube-system   kube-apiserver-k8s-master            1/1     Running   0          30m     172.29.56.175   k8s-master              
kube-system   kube-controller-manager-k8s-master   1/1     Running   0          30m     172.29.56.175   k8s-master              
kube-system   kube-flannel-ds-amd64-zr7jk          1/1     Running   0          2m51s   172.29.56.175   k8s-master              
kube-system   kube-proxy-tgn7p                     1/1     Running   0          31m     172.29.56.175   k8s-master              
kube-system   kube-scheduler-k8s-master            1/1     Running   0          30m     172.29.56.175   k8s-master              

需要注意，node上无需安装flannel，因为一旦加入集群，会自动起flannel容器。

测试集群DNS是否可用

[root@k8s-master k8s-install]# kubectl run curl --image=radial/busyboxplus:curl -it
kubectl run --generator=deployment/apps.v1 is DEPRECATED and will be removed in a future version. Use kubectl run --generator=run-pod/v1 or kubectl create instead.
If you don't see a command prompt, try pressing enter.
[ root@curl-6bf6db5c4f-mztwf:/ ]$

之后测试nslookup kubernetes.default是否能正常解析

Server:    10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local

Name:      kubernetes.default
Address 1: 10.96.0.1 kubernetes.default.svc.cluster.local

如果这一步DNS解析有问题，检查下CoreDNS的log，kubectl logs coredns-xxx -n kube-system，如果有no route to host的报错考虑是防火墙的原因（这是我自己遇到的）

添加Node节点

根据前面保存的添加node的脚本，在待添加的机器上跑一下

kubeadm join 172.29.56.175:6443 --token 085q2m.0dp7oldsibne4tv4 \
    --discovery-token-ca-cert-hash sha256:611c726b02601f18cec16a9aec8ef985d1236557b59029e56fd8e6d43fe04c81

之后在master上就可以查看了

[root@k8s-master k8s-init]# kubectl get nodes
NAME         STATUS   ROLES    AGE    VERSION
k8s-master   Ready    master   9m9s   v1.15.11
k8s-node1    Ready       2m     v1.15.11

总结

master的安装还是有点繁琐的，因为毕竟它是以后整个集群的大脑。相对而言，node节点只需要安装好了kubelet和kubeadm，确保能正常加入集群，很多事情就不用自己操心了，例如网络。

这一节只是确保了集群是正常可用的，但是还有很多的插件以及配置需要去个性化和调优，等到后面我们再慢慢探索和学习。

后续新版本Kubernetes的安装

本篇文章步骤参考自中文官方文档，后续有新版本Kubernetes，官方文档也会第一时间进行安装操作更新，大家可以持续关注。

也可以关注我的github仓库，有更新的测试可用的一键脚本我也会同步过去。