kubeadm是Kubernetes官方提供的用于快速安装Kubernetes集群的工具，伴随Kubernetes每个版本的发布都会同步更新，kubeadm会对集群配置方面的一些实践做调整，通过实验kubeadm可以学习到Kubernetes官方在集群配置上一些新的最佳实践。
在Kubernetes的文档Creating a single master cluster with kubeadm中已经给出了目前kubeadm的主要特性已经处于beta状态了，在2018年将进入GA状态，说明kubeadm离可以在生产环境中使用的距离越来越近了。
当然我们线上稳定运行的Kubernetes集群是使用ansible以二进制形式的部署的高可用集群，这里体验Kubernetes 1.12中的kubeadm是为了跟随官方对集群初始化和配置方面的最佳实践，进一步完善我们的ansible部署脚本。
1.准备
1.1系统配置
在安装之前，需要先做如下准备。两台CentOS 7.4主机如下：
cat /etc/hosts
192.168.61.11 node1
192.168.61.12 node2
如果各个主机启用了防火墙，需要开放Kubernetes各个组件所需要的端口，可以查看Installing kubeadm中的”Check required ports”一节。 这里简单起见在各节点禁用防火墙：
systemctl stop firewalld
systemctl disable firewalld
禁用SELINUX：
setenforce 0
vi /etc/selinux/config
SELINUX=disabled
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
执行命令使修改生效。
modprobe br_netfilter
sysctl -p /etc/sysctl.d/k8s.conf
1.2安装Docker
Kubernetes从1.6开始使用CRI(Container Runtime Interface)容器运行时接口。默认的容器运行时仍然是Docker，使用的是kubelet中内置dockershim CRI实现。
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
查看最新的Docker版本：
yum list docker-ce.x86_64 --showduplicates |sort -r
docker-ce.x86_64 18.06.1.ce-3.el7 docker-ce-stable
docker-ce.x86_64 18.06.0.ce-3.el7 docker-ce-stable
docker-ce.x86_64 18.03.1.ce-1.el7.centos docker-ce-stable
docker-ce.x86_64 18.03.0.ce-1.el7.centos docker-ce-stable
docker-ce.x86_64 17.12.1.ce-1.el7.centos docker-ce-stable
docker-ce.x86_64 17.12.0.ce-1.el7.centos docker-ce-stable
docker-ce.x86_64 17.09.1.ce-1.el7.centos docker-ce-stable
docker-ce.x86_64 17.09.0.ce-1.el7.centos docker-ce-stable
docker-ce.x86_64 17.06.2.ce-1.el7.centos docker-ce-stable
docker-ce.x86_64 17.06.1.ce-1.el7.centos docker-ce-stable
docker-ce.x86_64 17.06.0.ce-1.el7.centos docker-ce-stable
docker-ce.x86_64 17.03.3.ce-1.el7 docker-ce-stable
docker-ce.x86_64 17.03.2.ce-1.el7.centos docker-ce-stable
docker-ce.x86_64 17.03.1.ce-1.el7.centos docker-ce-stable
docker-ce.x86_64 17.03.0.ce-1.el7.centos docker-ce-stable
Kubernetes 1.12已经针对Docker的1.11.1, 1.12.1, 1.13.1, 17.03, 17.06, 17.09, 18.06等版本做了验证，需要注意Kubernetes 1.12最低支持的Docker版本是1.11.1。 我们这里在各节点安装docker的18.06.1版本。
yum makecache fast
yum install -y --setopt=obsoletes=0
docker-ce-18.06.1.ce-3.el7
systemctl start docker
systemctl enable docker
确认一下iptables filter表中FOWARD链的默认策略(pllicy)为ACCEPT。
iptables -nvL
Chain INPUT (policy ACCEPT 263 packets, 19209 bytes)
pkts bytes target prot opt in out source destination
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
0 0 DOCKER-USER all -- * * 0.0.0.0/0 0.0.0.0/0
0 0 DOCKER-ISOLATION-STAGE-1 all -- * * 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- * docker0 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED
0 0 DOCKER all -- * docker0 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- docker0 !docker0 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- docker0 docker0 0.0.0.0/0 0.0.0.0/0
Docker从1.13版本开始调整了默认的防火墙规则，禁用了iptables filter表中FOWARD链，这样会引起Kubernetes集群中跨Node的Pod无法通信。但这里通过安装docker 1806，发现默认策略又改回了ACCEPT，这个不知道是从哪个版本改回的，因为我们线上版本使用的1706还是需要手动调整这个策略的。
2.使用kubeadm部署Kubernetes
2.1 安装kubeadm和kubelet
下面在各节点安装kubeadm和kubelet：
cat <<EOF > /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
测试地址https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64是否可用，如果不可用需要科学上网。
curl https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
yum makecache fast
yum install -y kubelet kubeadm kubectl
...
Installed:
kubeadm.x86_64 0:1.12.0-0 kubectl.x86_64 0:1.12.0-0 kubelet.x86_64 0:1.12.0-0
Dependency Installed:
cri-tools.x86_64 0:1.11.1-0 kubernetes-cni.x86_64 0:0.6.0-0 socat.x86_64 0:1.7.3.2-2.el7
- 从安装结果可以看出还安装了cri-tools, kubernetes-cni, socat三个依赖：
- 官方从Kubernetes 1.9开始就将cni依赖升级到了0.6.0版本，在当前1.12中仍然是这个版本
- socat是kubelet的依赖
- cri-tools是CRI(Container Runtime Interface)容器运行时接口的命令行工具
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--config指定配置文件，并在配置文件中指定原来这些flag所配置的内容。具体内容可以查看这里Set Kubelet parameters via a config file。这也是Kubernetes为了支持动态Kubelet配置（Dynamic Kubelet Configuration）才这么做的，参考Reconfigure a Node’s Kubelet in a Live Cluster。
kubelet的配置文件必须是json或yaml格式，具体可查看这里。
Kubernetes 1.8开始要求关闭系统的Swap，如果不关闭，默认配置下kubelet将无法启动。
关闭系统的Swap方法如下:
swapoff -a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。
因为这里本次用于测试两台主机上还运行其他服务，关闭swap可能会对其他服务产生影响，所以这里修改kubelet的配置去掉这个限制。 之前的Kubernetes版本我们都是通过kubelet的启动参数--fail-swap-on=false去掉这个限制的。前面已经分析了Kubernetes不再推荐使用启动参数，而推荐使用配置文件。 所以这里我们改成配置文件配置的形式。
查看/etc/systemd/system/kubelet.service.d/10-kubeadm.conf，看到了下面的内容：
# Note: This dropin only works with kubeadm and kubelet v1.11+
[Service]
Environment="KUBELET_KUBECONFIG_ARGS=--bootstrap-kubeconfig=/etc/kubernetes/bootstrap-kubelet.conf --kubeconfig=/etc/kubernetes/kubelet.conf"
Environment="KUBELET_CONFIG_ARGS=--config=/var/lib/kubelet/config.yaml"
# This is a file that "kubeadm init" and "kubeadm join" generates at runtime, populating the KUBELET_KUBEADM_ARGS variable dynamically
EnvironmentFile=-/var/lib/kubelet/kubeadm-flags.env
# This is a file that the user can use for overrides of the kubelet args as a last resort. Preferably, the user should use
# the .NodeRegistration.KubeletExtraArgs object in the configuration files instead. KUBELET_EXTRA_ARGS should be sourced from this file.
EnvironmentFile=-/etc/sysconfig/kubelet
ExecStart=
ExecStart=/usr/bin/kubelet $KUBELET_KUBECONFIG_ARGS $KUBELET_CONFIG_ARGS $KUBELET_KUBEADM_ARGS $KUBELET_EXTRA_ARGS
上面显示kubeadm部署的kubelet的配置文件--config=/var/lib/kubelet/config.yaml，实际去查看/var/lib/kubelet和这个config.yaml的配置文件都没有被创建。 可以猜想肯定是运行kubeadm初始化集群时会自动生成这个配置文件，而如果我们不关闭Swap的话，第一次初始化集群肯定会失败的。
所以还是老老实实的回到使用kubelet的启动参数--fail-swap-on=false去掉必须关闭Swap的限制。 修改/etc/sysconfig/kubelet，加入：
KUBELET_EXTRA_ARGS=--fail-swap-on=false
2.2 使用kubeadm init初始化集群
在各节点开机启动kubelet服务：
systemctl enable kubelet.service
接下来使用kubeadm初始化集群，选择node1作为Master Node，在node1上执行下面的命令：
kubeadm init
--kubernetes-version=v1.12.0
--pod-network-cidr=10.244.0.0/16
--apiserver-advertise-address=192.168.61.11
因为我们选择flannel作为Pod网络插件，所以上面的命令指定–pod-network-cidr=10.244.0.0/16。
执行时报了下面的错误：
[init] using Kubernetes version: v1.12.0
[preflight] running pre-flight checks
[preflight] Some fatal errors occurred:
[ERROR Swap]: running with swap on is not supported. Please disable swap
[preflight] If you know what you are doing, you can make a check non-fatal with `--ignore-preflight-errors=...`
有一个错误信息是running with swap on is not supported. Please disable swap。因为我们决定配置failSwapOn: false，所以重新添加–ignore-preflight-errors=Swap参数忽略这个错误，重新运行。
kubeadm init
--kubernetes-version=v1.12.0
--pod-network-cidr=10.244.0.0/16
--apiserver-advertise-address=192.168.61.11
--ignore-preflight-errors=Swap
[init] using Kubernetes version: v1.12.0
[preflight] running pre-flight checks
[WARNING Swap]: running with swap on is not supported. Please disable swap
[preflight/images] Pulling images required for setting up a Kubernetes cluster
[preflight/images] This might take a minute or two, depending on the speed of your internet connection
[preflight/images] You can also perform this action in beforehand using 'kubeadm config images pull'
[kubelet] Writing kubelet environment file with flags to file "/var/lib/kubelet/kubeadm-flags.env"
[kubelet] Writing kubelet configuration to file "/var/lib/kubelet/config.yaml"
[preflight] Activating the kubelet service
[certificates] Generated etcd/ca certificate and key.
[certificates] Generated etcd/peer certificate and key.
[certificates] etcd/peer serving cert is signed for DNS names [node1 localhost] and IPs [192.168.61.11 127.0.0.1 ::1]
[certificates] Generated apiserver-etcd-client certificate and key.
[certificates] Generated etcd/server certificate and key.
[certificates] etcd/server serving cert is signed for DNS names [node1 localhost] and IPs [127.0.0.1 ::1]
[certificates] Generated etcd/healthcheck-client certificate and key.
[certificates] Generated ca certificate and key.
[certificates] Generated apiserver certificate and key.
[certificates] apiserver serving cert is signed for DNS names [node1 kubernetes kubernetes.default kubernetes.default.svc kubernetes.default.svc.cluster.local] and IPs [10.96.0.1 192.168.61.11]
[certificates] Generated apiserver-kubelet-client certificate and key.
[certificates] Generated front-proxy-ca certificate and key.
[certificates] Generated front-proxy-client certificate and key.
[certificates] valid certificates and keys now exist in "/etc/kubernetes/pki"
[certificates] Generated sa key and public key.
[kubeconfig] Wrote KubeConfig file to disk: "/etc/kubernetes/admin.conf"
[kubeconfig] Wrote KubeConfig file to disk: "/etc/kubernetes/kubelet.conf"
[kubeconfig] Wrote KubeConfig file to disk: "/etc/kubernetes/controller-manager.conf"
[kubeconfig] Wrote KubeConfig file to disk: "/etc/kubernetes/scheduler.conf"
[controlplane] wrote Static Pod manifest for component kube-apiserver to "/etc/kubernetes/manifests/kube-apiserver.yaml"
[controlplane] wrote Static Pod manifest for component kube-controller-manager to "/etc/kubernetes/manifests/kube-controller-manager.yaml"
[controlplane] wrote Static Pod manifest for component kube-scheduler to "/etc/kubernetes/manifests/kube-scheduler.yaml"
[etcd] Wrote Static Pod manifest for a local etcd instance to "/etc/kubernetes/manifests/etcd.yaml"
[init] waiting for the kubelet to boot up the control plane as Static Pods from directory "/etc/kubernetes/manifests"
[init] this might take a minute or longer if the control plane images have to be pulled
[apiclient] All control plane components are healthy after 26.503672 seconds
[uploadconfig] storing the configuration used in ConfigMap "kubeadm-config" in the "kube-system" Namespace
[kubelet] Creating a ConfigMap "kubelet-config-1.12" in namespace kube-system with the configuration for the kubelets in the cluster
[markmaster] Marking the node node1 as master by adding the label "node-role.kubernetes.io/master=''"
[markmaster] Marking the node node1 as master by adding the taints [node-role.kubernetes.io/master:NoSchedule]
[patchnode] Uploading the CRI Socket information "/var/run/dockershim.sock" to the Node API object "node1" as an annotation
[bootstraptoken] using token: zalj3i.q831ehufqb98d1ic
[bootstraptoken] configured RBAC rules to allow Node Bootstrap tokens to post CSRs in order for nodes to get long term certificate credentials
[bootstraptoken] configured RBAC rules to allow the csrapprover controller automatically approve CSRs from a Node Bootstrap Token
[bootstraptoken] configured RBAC rules to allow certificate rotation for all node client certificates in the cluster
[bootstraptoken] creating the "cluster-info" ConfigMap in the "kube-public" namespace
[addons] Applied essential addon: CoreDNS
[addons] Applied essential addon: kube-proxy
Your Kubernetes master 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/
You can now join any number of machines by running the following on each node
as root:
kubeadm join 192.168.61.11:6443 --token zalj3i.q831ehufqb98d1ic --discovery-token-ca-cert-hash sha256:6ee48b19ba61a2dda77f6b60687c5fd11072ab898cfdfef32a68821d1dbe8efa
上面记录了完成的初始化输出的内容，根据输出的内容基本上可以看出手动初始化安装一个Kubernetes集群所需要的关键步骤。
其中有以下关键内容：
[kubelet]生成kubelet的配置文件”/var/lib/kubelet/config.yaml”[certificates]生成相关的各种证书[kubeconfig]生成相关的kubeconfig文件[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- 下面的命令是配置常规用户如何使用kubectl访问集群：
mkdir -p $HOME/.kube sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config sudo chown $(id -u):$(id -g) $HOME/.kube/config- 最后给出了将节点加入集群的命令
kubeadm join 192.168.61.11:6443 --token zalj3i.q831ehufqb98d1ic --discovery-token-ca-cert-hash sha256:6ee48b19ba61a2dda77f6b60687c5fd11072ab898cfdfef32a68821d1dbe8efa
查看一下集群状态：
kubectl get cs
NAME STATUS MESSAGE ERROR
controller-manager Healthy ok
scheduler Healthy ok
etcd-0 Healthy {"health": "true"}
确认个组件都处于healthy状态。
集群初始化如果遇到问题，可以使用下面的命令进行清理：
kubeadm reset
ifconfig cni0 down
ip link delete cni0
ifconfig flannel.1 down
ip link delete flannel.1
rm -rf /var/lib/cni/
2.3 安装Pod Network
接下来安装flannel network add-on：
mkdir -p ~/k8s/
cd ~/k8s
wget https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml
kubectl apply -f kube-flannel.yml
clusterrole.rbac.authorization.k8s.io/flannel created
clusterrolebinding.rbac.authorization.k8s.io/flannel created
serviceaccount/flannel created
configmap/kube-flannel-cfg created
daemonset.extensions/kube-flannel-ds-amd64 created
daemonset.extensions/kube-flannel-ds-arm64 created
daemonset.extensions/kube-flannel-ds-arm created
daemonset.extensions/kube-flannel-ds-ppc64le created
daemonset.extensions/kube-flannel-ds-s390x created
这里注意kube-flannel.yml这个文件里的flannel的镜像是0.10.0，quay.io/coreos/flannel:v0.10.0-amd64
如果Node有多个网卡的话，参考flannel issues 39701，目前需要在kube-flannel.yml中使用--iface参数指定集群主机内网网卡的名称，否则可能会出现dns无法解析。需要将kube-flannel.yml下载到本地，flanneld启动参数加上--iface=<iface-name>
......
containers:
- name: kube-flannel
image: quay.io/coreos/flannel:v0.10.0-amd64
command:
- /opt/bin/flanneld
args:
- --ip-masq
- --kube-subnet-mgr
- --iface=eth1
......
本次按上面的步骤部署flannel，发现没有效果，查看一下集群中的daemonset：
kubectl get ds -l app=flannel -n kube-system
NAME DESIRED CURRENT READY UP-TO-DATE AVAILABLE NODE SELECTOR AGE
kube-flannel-ds-amd64 0 0 0 0 0 beta.kubernetes.i/oarch=amd64 17s
kube-flannel-ds-arm 0 0 0 0 0 beta.kubernetes.io/arch=arm 17s
kube-flannel-ds-arm64 0 0 0 0 0 beta.kubernetes.io/arch=arm64 17s
kube-flannel-ds-ppc64le 0 0 0 0 0 beta.kubernetes.io/arch=ppc64le 17s
kube-flannel-ds-s390x 0 0 0 0 0 beta.kubernetes.io/arch=s390x 17s
结合kube-flannel.yml，fannel官方的部署yaml文件是要在集群中创建5个针对不同平台的DaemonSet，通过Node的Label beta.kubernetes.i/oarch，在对应不同平台的Node节点上启动flannel的容器。当前的node1节点是beta.kubernetes.i/oarch=amd64，因此对于kube-flannel-ds-amd64这个DaemonSet来说，它的DESIRED数量应该为1才对。查看kube-flannel.yml中关于kube-flannel-ds-amd64的内容：
spec:
template:
metadata:
labels:
tier: node
app: flannel
spec:
hostNetwork: true
nodeSelector:
beta.kubernetes.io/arch: amd64
tolerations:
- key: node-role.kubernetes.io/master
operator: Exists
effect: NoSchedule
kube-flannel.yml中已经为kube-flannel-ds-amd64正确设置了调度相关的nodeSelector和tolerations，即将这个DaemonSet的Pod调度到Label为beta.kubernetes.io/arch: amd64，同时容忍node-role.kubernetes.io/master:NoSchedule污点的节点上。这个按照以前的部署经验来说当前的主节点node1应该是多满足的，可是现在是这样的吗？我们查看一下node1节点的基本信息：
kubectl describe node node1
Name: node1
Roles: master
Labels: beta.kubernetes.io/arch=amd64
beta.kubernetes.io/os=linux
kubernetes.io/hostname=node1
node-role.kubernetes.io/master=
Annotations: kubeadm.alpha.kubernetes.io/cri-socket: /var/run/dockershim.sock
node.alpha.kubernetes.io/ttl: 0
volumes.kubernetes.io/controller-managed-attach-detach: true
CreationTimestamp: Wed, 03 Oct 2018 09:03:04 +0800
Taints: node-role.kubernetes.io/master:NoSchedule
node.kubernetes.io/not-ready:NoSchedule
Unschedulable: false
可以看到1.12版本的kubeadm额外给node1节点设置了一个污点(Taint)：node.kubernetes.io/not-ready:NoSchedule，很容易理解，即如果节点还没有ready之前，是不接受调度的。可是如果Kubernetes的网络插件还没有部署的话，节点是不会进入ready状态的。因此我们修改以下kube-flannel.yaml的内容，加入对node.kubernetes.io/not-ready:NoSchedule这个污点的容忍：
tolerations:
- key: node-role.kubernetes.io/master
operator: Exists
effect: NoSchedule
- key: node.kubernetes.io/not-ready
operator: Exists
effect: NoSchedule
重新apply一下kubectl apply -f kube-flannel.yml，这次成功完成flannel的部署了。
使用kubectl get pod --all-namespaces -o wide确保所有的Pod都处于Running状态。
kubectl get pod --all-namespaces -o wide
NAMESPACE NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE
kube-system coredns-576cbf47c7-njt7l 1/1 Running 0 12m 10.244.0.3 node1 <none>
kube-system coredns-576cbf47c7-vg2gd 1/1 Running 0 12m 10.244.0.2 node1 <none>
kube-system etcd-node1 1/1 Running 0 12m 192.168.61.11 node1 <none>
kube-system kube-apiserver-node1 1/1 Running 0 12m 192.168.61.11 node1 <none>
kube-system kube-controller-manager-node1 1/1 Running 0 12m 192.168.61.11 node1 <none>
kube-system kube-flannel-ds-amd64-bxtqh 1/1 Running 0 2m 192.168.61.11 node1 <none>
kube-system kube-proxy-fb542 1/1 Running 0 12m 192.168.61.11 node1 <none>
kube-system kube-scheduler-node1 1/1 Running 0 12m 192.168.61.11 node1 <none>
后来也在flannel的github中找到了关于node.kubernetes.io/not-ready:NoSchedule这个问题的讨论，相信很快就会将相关配置修改正确，详见https://github.com/coreos/flannel/issues/1044。
2.4 master node参与工作负载
使用kubeadm初始化的集群，出于安全考虑Pod不会被调度到Master Node上，也就是说Master Node不参与工作负载。这是因为当前的master节点node1被打上了node-role.kubernetes.io/master:NoSchedule的污点：
kubectl describe node node1 | grep Taint
Taints: node-role.kubernetes.io/master:NoSchedule
因为这里搭建的是测试环境，去掉这个污点使node1参与工作负载：
kubectl taint nodes node1 node-role.kubernetes.io/master-
node "node1" untainted
2.5 测试DNS
kubectl run curl --image=radial/busyboxplus:curl -it
kubectl run --generator=deployment/apps.v1beta1 is DEPRECATED and will be removed in a future version. Use kubectl create instead.
If you don't see a command prompt, try pressing enter.
[ root@curl-5cc7b478b6-r997p:/ ]$
进入后执行nslookup kubernetes.default确认解析正常:
nslookup kubernetes.default
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
2.6 向Kubernetes集群中添加Node节点
下面我们将node2这个主机添加到Kubernetes集群中，因为我们同样在node2上的kubelet的启动参数中去掉了必须关闭swap的限制，所以同样需要--ignore-preflight-errors=Swap这个参数。 在node2上执行:
kubeadm join 192.168.61.11:6443 --token zalj3i.q831ehufqb98d1ic --discovery-token-ca-cert-hash sha256:6ee48b19ba61a2dda77f6b60687c5fd11072ab898cfdfef32a68821d1dbe8efa
--ignore-preflight-errors=Swap
[preflight] running pre-flight checks
[WARNING RequiredIPVSKernelModulesAvailable]: the IPVS proxier will not be used, because the following required kernel modules are not loaded: [ip_vs_rr ip_vs_wrr ip_vs_sh ip_vs] or no builtin kernel ipvs support: map[ip_vs:{} ip_vs_rr:{} ip_vs_wrr:{} ip_vs_sh:{} nf_conntrack_ipv4:{}]
you can solve this problem with following methods:
1. Run 'modprobe -- ' to load missing kernel modules;
2. Provide the missing builtin kernel ipvs support
[WARNING Swap]: running with swap on is not supported. Please disable swap
[discovery] Trying to connect to API Server "192.168.61.11:6443"
[discovery] Created cluster-info discovery client, requesting info from "https://192.168.61.11:6443"
[discovery] Requesting info from "https://192.168.61.11:6443" again to validate TLS against the pinned public key
[discovery] Cluster info signature and contents are valid and TLS certificate validates against pinned roots, will use API Server "192.168.61.11:6443"
[discovery] Successfully established connection with API Server "192.168.61.11:6443"
[kubelet] Downloading configuration for the kubelet from the "kubelet-config-1.12" ConfigMap in the kube-system namespace
[kubelet] Writing kubelet configuration to file "/var/lib/kubelet/config.yaml"
[kubelet] Writing kubelet environment file with flags to file "/var/lib/kubelet/kubeadm-flags.env"
[preflight] Activating the kubelet service
[tlsbootstrap] Waiting for the kubelet to perform the TLS Bootstrap...
[patchnode] Uploading the CRI Socket information "/var/run/dockershim.sock" to the Node API object "node2" as an annotation
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 master to see this node join the cluster.
node2加入集群很是顺利，下面在master节点上执行命令查看集群中的节点：
kubectl get nodes
NAME STATUS ROLES AGE VERSION
node1 Ready master 26m v1.12.0
node2 Ready <none> 2m v1.12.0
如何从集群中移除Node
如果需要从集群中移除node2这个Node执行下面的命令：
在master节点上执行：
kubectl drain node2 --delete-local-data --force --ignore-daemonsets
kubectl delete node node2
在node2上执行：
kubeadm reset
ifconfig cni0 down
ip link delete cni0
ifconfig flannel.1 down
ip link delete flannel.1
rm -rf /var/lib/cni/
在node1上执行：
kubectl delete node node2
3.Kubernetes常用组件部署
越来越多的公司和团队开始使用Helm这个Kubernetes的包管理器，我们也将使用Helm安装Kubernetes的常用组件。
3.1 Helm的安装
Helm由客户端命helm令行工具和服务端tiller组成，Helm的安装十分简单。 下载helm命令行工具到master节点node1的/usr/local/bin下，这里下载的2.9.1版本：
wget https://storage.googleapis.com/kubernetes-helm/helm-v2.11.0-linux-amd64.tar.gz
tar -zxvf helm-v2.11.0-linux-amd64.tar.gz
cd linux-amd64/
cp helm /usr/local/bin/
为了安装服务端tiller，还需要在这台机器上配置好kubectl工具和kubeconfig文件，确保kubectl工具可以在这台机器上访问apiserver且正常使用。 这里的node1节点以及配置好了kubectl。
因为Kubernetes APIServer开启了RBAC访问控制，所以需要创建tiller使用的service account: tiller并分配合适的角色给它。 详细内容可以查看helm文档中的Role-based Access Control。 这里简单起见直接分配cluster-admin这个集群内置的ClusterRole给它。创建rbac-config.yaml文件：
apiVersion: v1
kind: ServiceAccount
metadata:
name: tiller
namespace: kube-system
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
name: tiller
roleRef:
apiGroup: rbac.authorization.k8s.io
kind: ClusterRole
name: cluster-admin
subjects:
- kind: ServiceAccount
name: tiller
namespace: kube-system
kubectl create -f rbac-config.yaml
serviceaccount/tiller created
clusterrolebinding.rbac.authorization.k8s.io/tiller created
接下来使用helm部署tiller:
helm init --service-account tiller --skip-refresh
Creating /root/.helm
Creating /root/.helm/repository
Creating /root/.helm/repository/cache
Creating /root/.helm/repository/local
Creating /root/.helm/plugins
Creating /root/.helm/starters
Creating /root/.helm/cache/archive
Creating /root/.helm/repository/repositories.yaml
Adding stable repo with URL: https://kubernetes-charts.storage.googleapis.com
Adding local repo with URL: http://127.0.0.1:8879/charts
$HELM_HOME has been configured at /root/.helm.
Tiller (the Helm server-side component) has been installed into your Kubernetes Cluster.
Please note: by default, Tiller is deployed with an insecure 'allow unauthenticated users' policy.
To prevent this, run `helm init` with the --tiller-tls-verify flag.
For more information on securing your installation see: https://docs.helm.sh/using_helm/#securing-your-helm-installation
Happy Helming!
tiller默认被部署在k8s集群中的kube-system这个namespace下：
kubectl get pod -n kube-system -l app=helm
NAME READY STATUS RESTARTS AGE
tiller-deploy-6f6fd74b68-kk2z9 1/1 Running 0 3m17s
helm version
Client: &version.Version{SemVer:"v2.11.0", GitCommit:"2e55dbe1fdb5fdb96b75ff144a339489417b146b", GitTreeState:"clean"}
Server: &version.Version{SemVer:"v2.11.0", GitCommit:"2e55dbe1fdb5fdb96b75ff144a339489417b146b", GitTreeState:"clean"}
注意由于某些原因需要网络可以访问gcr.io和kubernetes-charts.storage.googleapis.com，如果无法访问可以通过
helm init --service-account tiller --tiller-image <your-docker-registry>/tiller:v2.11.0 --skip-refresh使用私有镜像仓库中的tiller镜像
3.2 使用Helm部署Nginx Ingress
为了便于将集群中的服务暴露到集群外部，从集群外部访问，接下来使用Helm将Nginx Ingress部署到Kubernetes上。 Nginx Ingress Controller被部署在Kubernetes的边缘节点上，关于Kubernetes边缘节点的高可用相关的内容可以查看我前面整理的Bare metal环境下Kubernetes Ingress边缘节点的高可用。 这里简单起见，只有一个edge节点。
我们将node1(192.168.61.11)同时做为边缘节点，打上Label：
kubectl label node node1 node-role.kubernetes.io/edge=
node/node1 labeled
kubectl get node
NAME STATUS ROLES AGE VERSION
node1 Ready edge,master 46m v1.12.0
node2 Ready <none> 22m v1.12.0
stable/nginx-ingress chart的值文件ingress-nginx.yaml：
controller:
service:
externalIPs:
- 192.168.61.11
nodeSelector:
node-role.kubernetes.io/edge: ''
tolerations:
- key: node-role.kubernetes.io/master
operator: Exists
effect: NoSchedule
defaultBackend:
nodeSelector:
node-role.kubernetes.io/edge: ''
tolerations:
- key: node-role.kubernetes.io/master
operator: Exists
effect: NoSchedule
helm repo update
helm install stable/nginx-ingress
-n nginx-ingress
--namespace ingress-nginx
-f ingress-nginx.yaml
kubectl get pod -n ingress-nginx -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE
nginx-ingress-controller-7577b57874-m4zkv 1/1 Running 0 9m13s 10.244.0.10 node1 <none>
nginx-ingress-default-backend-684f76869d-9jgtl 1/1 Running 0 9m13s 10.244.0.9 node1 <none>
如果访问http://192.168.61.11返回default backend，则部署完成:
curl http://192.168.61.11/
default backend - 404
3.2 将TLS证书配置到Kubernetes中
当使用Ingress将HTTPS的服务暴露到集群外部时，需要HTTPS证书，这里将*.frognew.com的证书和秘钥配置到Kubernetes中。
后边部署在kube-system命名空间中的dashboard要使用这个证书，因此这里先在kube-system中创建证书的secret
kubectl create secret tls frognew-com-tls-secret --cert=fullchain.pem --key=privkey.pem -n kube-system
secret/frognew-com-tls-secret created
3.3 使用Helm部署dashboard
kubernetes-dashboard.yaml：
ingress:
enabled: true
hosts:
- k8s.frognew.com
annotations:
nginx.ingress.kubernetes.io/ssl-redirect: "true"
nginx.ingress.kubernetes.io/secure-backends: "true"
tls:
- secretName: frognew-com-tls-secret
hosts:
- k8s.frognew.com
rbac:
clusterAdminRole: true
helm install stable/kubernetes-dashboard
-n kubernetes-dashboard
--namespace kube-system
-f kubernetes-dashboard.yaml
kubectl -n kube-system get secret | grep kubernetes-dashboard-token
kubernetes-dashboard-token-tjj25 kubernetes.io/service-account-token 3 37s
kubectl describe -n kube-system secret/kubernetes-dashboard-token-tjj25
Name: kubernetes-dashboard-token-tjj25
Namespace: kube-system
Labels: <none>
Annotations: kubernetes.io/service-account.name=kubernetes-dashboard
kubernetes.io/service-account.uid=d19029f0-9cac-11e8-8d94-080027db403a
Type: kubernetes.io/service-account-token
Data
====
namespace: 11 bytes
token: eyJhbGciOiJSUzI1NiIsImtpZCI6IiJ9.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.w1HZrtBOhANdqSRLNs22z8dQWd5IOCpEl9VyWQ6DUwhHfgpAlgdhEjTqH8TT0f4ftu_eSPnnUXWbsqTNDobnlxet6zVvZv1K-YmIO-o87yn2PGIrcRYWkb-ADWD6xUWzb0xOxu2834BFVC6T5p5_cKlyo5dwerdXGEMoz9OW0kYvRpKnx7E61lQmmacEeizq7hlIk9edP-ot5tCuIO_gxpf3ZaEHnspulceIRO_ltjxb8SvqnMglLfq6Bt54RpkUOFD1EKkgWuhlXJ8c9wJt_biHdglJWpu57tvOasXtNWaIzTfBaTiJ3AJdMB_n0bQt5CKAUnKBhK09NP3R0Qtqog
在dashboard的登录窗口使用上面的token登录。
3.4 使用Helm部署metrics-server
从Heapster的github https://github.com/kubernetes/heapster中可以看到已经，heapster已经DEPRECATED。这里heapster的deprecation timeline。可以看出heapster从Kubernetes 1.12开始将从Kubernetes各种安装脚本中移除。
Kubernetes推荐使用metrics-server(https://github.com/kubernetes-incubator/metrics-server)。我们这里也使用helm来部署metrics-server。
metrics-server.yaml:
args:
- --logtostderr
- --kubelet-insecure-tls
helm install stable/metrics-server
-n metrics-server
--namespace kube-system
-f metrics-server.yaml
部署后，查看metrics-server的日志，报下面的错误：
E1003 05:46:13.757009 1 manager.go:102] unable to fully collect metrics: [unable to fully scrape metrics from source kubelet_summary:node1: unable to fetch metrics from Kubelet node1 (node1): Get https://node1:10250/stats/summary/: dial tcp: lookup node1 on 10.96.0.10:53: no such host, unable to fully scrape metrics from source kubelet_summary:node2: unable to fetch metrics from Kubelet node2 (node2): Get https://node2:10250/stats/summary/: dial tcp: lookup node2 on 10.96.0.10:53: read udp 10.244.1.6:45288->10.96.0.10:53: i/o timeout]
可以看到metrics-server在从kubelet的10250端口获取信息时，使用的是hostname，而因为node1和node2是一个独立的演示环境，只是修改了这两个节点系统的/etc/hosts文件，而并没有内网的DNS服务器，所以metrics-server中不认识node1和node2的名字。这里我们可以直接修改Kubernetes集群中的coredns的configmap，修改Corefile加入hostnames插件，将Kubernetes的各个节点的主机名加入到hostnames中，这样Kubernetes集群中的所有Pod都可以从CoreDNS中解析各个节点的名字。
kubectl edit configmap coredns -n kube-system
apiVersion: v1
data:
Corefile: |
.:53 {
errors
health
hosts {
192.168.61.11 node1
192.168.61.12 node2
fallthrough
}
kubernetes cluster.local in-addr.arpa ip6.arpa {
pods insecure
upstream
fallthrough in-addr.arpa ip6.arpa
}
prometheus :9153
proxy . /etc/resolv.conf
cache 30
loop
reload
loadbalance
}
kind: ConfigMap
配置修改完毕后重启集群中coredns和metrics-server，确认metrics-server不再有错误日志。使用下面的命令可以获取到关于集群节点基本的指标信息：
kubectl get --raw "/apis/metrics.k8s.io/v1beta1/nodes"
遗憾的是，当前Kubernetes Dashboard还不支持metrics-server。因此如果使用metrics-server替代了heapster，将无法在dashboard中以图形展示Pod的内存和CPU情况(实际上这也不是很重要，当前我们是在Prometheus和Grafana中定制的Kubernetes集群中各个Pod的监控，因此在dashboard中查看Pod内存和CPU也不是很重要)。 Dashboard的github上有很多这方面的讨论，如
https://github.com/kubernetes/dashboard/issues/3217和https://github.com/kubernetes/dashboard/issues/3270，Dashboard已经准备在将来的某个时间点支持metrics-server。但由于metrics-server和metrics pipeline肯定是Kubernetes在monitor方面未来的方向，所以我们也很果断的在各个环境中切换到了metrics-server。
4.总结
本次安装涉及到的Docker镜像：
# kubernetes
k8s.gcr.io/kube-apiserver:v1.12.0
k8s.gcr.io/kube-controller-manager:v1.12.0
k8s.gcr.io/kube-scheduler:v1.12.0
k8s.gcr.io/kube-proxy:v1.12.0
k8s.gcr.io/etcd:3.2.24
k8s.gcr.io/pause:3.1
# network and dns
quay.io/coreos/flannel:v0.10.0-amd64
k8s.gcr.io/coredns:1.2.2
# helm and tiller
gcr.io/kubernetes-helm/tiller:v2.11.0
# nginx ingress
quay.io/kubernetes-ingress-controller/nginx-ingress-controller:0.19.0
k8s.gcr.io/defaultbackend:1.4
# dashboard and metric-sever
k8s.gcr.io/kubernetes-dashboard-amd64:v1.10.0
gcr.io/google_containers/metrics-server-amd64:v0.3.0