13. 第十二篇 二进制安装kubelet

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本文是二进制安装kubernetes v1.17.0的第十二篇，kubelet组件需要运行的所有节点上面（因为我们所有节点都运行Pod，包括Master节点），因为kubelet是运行Pod必须的组件，由它接收kube-apiserver发送的请求，管理此节点Pod及Pod内的容器，并且kubelet新版本内置了cAdvisor，通过它监控容器和节点资源，并定期向Master节点汇报资源使用情况等；

下载https://dl.k8s.io/v1.17.0/kubernetes-node-linux-amd64.tar.gz，二进制安装包中含有kubernetes/node/bin/kubeadm与kubernetes/node/bin/kubelet等其它文件，本篇我们使用到kubeadm与kubelet，把kubeadm copy到中控机的/data/k8s/bin/目录，把kubelet分发到所有节点上面/data/k8s/bin/目录。

创建kubelet引导配置文件

这里kubelet程序启动时使用引导令牌认证，即Bootstrap Token Auth。

kubelet启动时查找--kubeletconfig参数对应的文件是否存在，如果不存在则使用--bootstrap-kubeconfig参数指定的kubeconfig 文件，向kube-apiserver发送证书签名请求(CertificateSigningRequest，简称CSR)，kube-apiserver收到CSR请求后，对其中的 Token进行认证，当认证请求被approve（批准、赞成）后，并将请求的user设置为system:bootstrap:，请求的group 设置为system:bootstrappers，这一过程称为Bootstrap Token Auth，并且当CSR请求被批准后，kube-controller-manager会为kubelet创建TLS客户端证书、私钥并创建--kubeconfig参数指定的文件中，这个文件即是kubelet访问kube-apiserver使用的认证文件。

说明：

1. kube-controller-manager需要配置-–cluster-signing-cert-file和-–cluster-signing-key-file参数，才会为TLS Bootstrap 创建证书和私钥；
2. 证书和私钥存放在-cert-dir参数指定的目录中；

由于所有节点都需要与kube-apiserver通信，即每个节点上面的kubelet作为客户端，kube-apiserver程序作为服务器，客户端访问kube-apiserver需要验证和认证，并且每个节点都不相同，所以需要为每个节点创建一个kubelet引导配置文件，然后启动时由kube-controller-manager生成证书和私钥，并创建kubeconfig配置文件供kubelet访问kube-apiserver使用。下面为每个节点创建kubelet引导配置文件并分发；

#!/bin/bash

cd /data/k8s/work
source /data/k8s/bin/env.sh

for node_name in ${NODE_NAMES[@]}
do
    echo ">>> ${node_name}"
    export BOOTSTRAP_TOKEN=$(kubeadm token create \
      --description kubelet-bootstrap-token \
      --groups system:bootstrappers:${node_name} \
      --kubeconfig ~/.kube/config)
    kubectl config set-cluster kubernetes \
      --certificate-authority=/etc/kubernetes/cert/ca.pem \
      --embed-certs=true \
      --server=${KUBE_APISERVER} \
      --kubeconfig=kubelet-bootstrap-${node_name}.kubeconfig
    kubectl config set-credentials kubelet-bootstrap \
      --token=${BOOTSTRAP_TOKEN} \
      --kubeconfig=kubelet-bootstrap-${node_name}.kubeconfig
    kubectl config set-context default \
      --cluster=kubernetes \
      --user=kubelet-bootstrap \
      --kubeconfig=kubelet-bootstrap-${node_name}.kubeconfig
    kubectl config use-context default --kubeconfig=kubelet-bootstrap-${node_name}.kubeconfig
done

# 分发
for node_name in ${NODE_NAMES[@]}
do
    echo ">>> ${node_name}"
    scp kubelet-bootstrap-${node_name}.kubeconfig root@${node_name}:/etc/kubernetes/kubelet-bootstrap.kubeconfig
done

从上面可知，我们向kubectl引导配置文件中写入的是Token，而kubeadm token create创建的Token，有效期默认是1天，如果kubelet在有效期内没有使用它引导的话，将kube-controller-manager清理掉，如果kubelet使用它引导结束后，kube-controller-manager会为kubelet创建各自的client和server证书等。

查看kubeadm创建的token

kubeadm token list --kubeconfig ~/.kube/config

创建user和group的CSR权限

根据上面Bootstrap Token Auth认证得知，kubelet启动时，kube-apiserver approve后会将请求的user设置为system:bootstrap:，请求group 设置为system:bootstrappers，但前提需要授权，否则启动kubelet时会失败；

kubectl create clusterrolebinding kubelet-bootstrap --clusterrole=system:node-bootstrapper --group=system:bootstrappers

创建配置模板并分发

#!/bin/bash

cd /data/k8s/work
source /data/k8s/bin/env.sh

cat > kubelet-config.yaml.template <<EOF
kind: KubeletConfiguration
apiVersion: kubelet.config.k8s.io/v1beta1
address: "##NODE_IP##"
staticPodPath: ""
syncFrequency: 1m
fileCheckFrequency: 20s
httpCheckFrequency: 20s
staticPodURL: ""
port: 10250
readOnlyPort: 0
rotateCertificates: true
serverTLSBootstrap: true
authentication:
  anonymous:
    enabled: false
  webhook:
    enabled: true
  x509:
    clientCAFile: "/etc/kubernetes/cert/ca.pem"
authorization:
  mode: Webhook
registryPullQPS: 0
registryBurst: 20
eventRecordQPS: 0
eventBurst: 20
enableDebuggingHandlers: true
enableContentionProfiling: true
healthzPort: 10248
healthzBindAddress: "##NODE_IP##"
clusterDomain: "${CLUSTER_DNS_DOMAIN}"
clusterDNS:
  - "${CLUSTER_DNS_SVC_IP}"
nodeStatusUpdateFrequency: 10s
nodeStatusReportFrequency: 1m
imageMinimumGCAge: 2m
imageGCHighThresholdPercent: 85
imageGCLowThresholdPercent: 80
volumeStatsAggPeriod: 1m
kubeletCgroups: ""
systemCgroups: ""
cgroupRoot: ""
cgroupsPerQOS: true
cgroupDriver: systemd
runtimeRequestTimeout: 10m
hairpinMode: promiscuous-bridge
maxPods: 220
podCIDR: "${CLUSTER_CIDR}"
podPidsLimit: -1
resolvConf: /etc/resolv.conf
maxOpenFiles: 1000000
kubeAPIQPS: 1000
kubeAPIBurst: 2000
serializeImagePulls: false
evictionHard:
  memory.available: "100Mi"
  nodefs.available: "10%"
  nodefs.inodesFree: "5%"
  imagefs.available: "15%"
evictionSoft: {}
enableControllerAttachDetach: true
failSwapOn: true
containerLogMaxSize: 20Mi
containerLogMaxFiles: 10
systemReserved: {}
kubeReserved: {}
systemReservedCgroup: ""
kubeReservedCgroup: ""
enforceNodeAllocatable: ["pods"]
EOF

# 分发
for node_ip in ${NODE_IPS[@]}
do
    echo ">>> ${node_ip}"
    sed -e "s/##NODE_IP##/${node_ip}/" kubelet-config.yaml.template > kubelet-config-${node_ip}.yaml.template
    scp kubelet-config-${node_ip}.yaml.template root@${node_ip}:/etc/kubernetes/kubelet-config.yaml
done

配置详解

创建启动文件并分发

#!/bin/bash

cd /data/k8s/work
source /data/k8s/bin/env.sh

cat > kubelet.service.template <<EOF
[Unit]
Description=Kubernetes Kubelet
Documentation=https://github.com/GoogleCloudPlatform/kubernetes
After=docker.service
Requires=docker.service
[Service]
WorkingDirectory=${K8S_DIR}/kubelet
ExecStart=/data/k8s/bin/kubelet \\
  --bootstrap-kubeconfig=/etc/kubernetes/kubelet-bootstrap.kubeconfig \\
  --cert-dir=/etc/kubernetes/cert \\
  --cni-conf-dir=/etc/cni/net.d \\
  --container-runtime=docker \\
  --container-runtime-endpoint=unix:///var/run/dockershim.sock \\
  --root-dir=${K8S_DIR}/kubelet \\
  --kubeconfig=/etc/kubernetes/kubelet.kubeconfig \\
  --config=/etc/kubernetes/kubelet-config.yaml \\
  --hostname-override=##NODE_NAME## \\
  --pod-infra-container-image=gcr.azk8s.cn/google_containers/pause-amd64:3.1 \\
  --image-pull-progress-deadline=15m \\
  --volume-plugin-dir=${K8S_DIR}/kubelet/kubelet-plugins/volume/exec/ \\
  --logtostderr=true \\
  --v=2
Restart=always
RestartSec=5
StartLimitInterval=0
[Install]
WantedBy=multi-user.target
EOF

# 分发
for node_name in ${NODE_NAMES[@]}
do
    echo ">>> ${node_name}"
    sed -e "s/##NODE_NAME##/${node_name}/" kubelet.service.template > kubelet-${node_name}.service
    scp kubelet-${node_name}.service root@${node_name}:/etc/systemd/system/kubelet.service
done

配置参数详解

启动服务

#!/bin/bash

cd /data/k8s/work
source /data/k8s/bin/env.sh

for node_ip in ${NODE_IPS[@]}
do
    echo ">>> ${node_ip}"
    ssh root@${node_ip} "mkdir -p ${K8S_DIR}/kubelet/kubelet-plugins/volume/exec/"
    ssh root@${node_ip} "/usr/sbin/swapoff -a"
    ssh root@${node_ip} "systemctl daemon-reload && systemctl enable kubelet && systemctl restart kubelet"
done

服务启动后查看CSR，均处于Pending状态，需要approve后才可以通过

kubectl get csr

下面创建自动审批机制

创建ClusterRoleBinding自动approve

#!/bin/bash

cd /data/k8s/work
cat > auto-csr-for-kubelet.yaml <<EOF
 # Approve all CSRs for the group "system:bootstrappers"
 kind: ClusterRoleBinding
 apiVersion: rbac.authorization.k8s.io/v1
 metadata:
   name: auto-approve-csrs-for-group
 subjects:
 - kind: Group
   name: system:bootstrappers
   apiGroup: rbac.authorization.k8s.io
 roleRef:
   kind: ClusterRole
   name: system:certificates.k8s.io:certificatesigningrequests:nodeclient
   apiGroup: rbac.authorization.k8s.io
---
 # To let a node of the group "system:nodes" renew its own credentials
 kind: ClusterRoleBinding
 apiVersion: rbac.authorization.k8s.io/v1
 metadata:
   name: node-client-cert-renewal
 subjects:
 - kind: Group
   name: system:nodes
   apiGroup: rbac.authorization.k8s.io
 roleRef:
   kind: ClusterRole
   name: system:certificates.k8s.io:certificatesigningrequests:selfnodeclient
   apiGroup: rbac.authorization.k8s.io
---
# A ClusterRole which instructs the CSR approver to approve a node requesting a
# serving cert matching its client cert.
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: approve-node-server-renewal-csr
rules:
- apiGroups: ["certificates.k8s.io"]
  resources: ["certificatesigningrequests/selfnodeserver"]
  verbs: ["create"]
---
 # To let a node of the group "system:nodes" renew its own server credentials
 kind: ClusterRoleBinding
 apiVersion: rbac.authorization.k8s.io/v1
 metadata:
   name: node-server-cert-renewal
 subjects:
 - kind: Group
   name: system:nodes
   apiGroup: rbac.authorization.k8s.io
 roleRef:
   kind: ClusterRole
   name: approve-node-server-renewal-csr
   apiGroup: rbac.authorization.k8s.io
EOF

kubectl apply -f auto-csr-for-kubelet.yaml

auto-approve-csrs-for-group 自动approve node的第一次CSR，注意第一次CSR时，请求的Group为system:bootstrappers；

node-client-cert-renewal 自动approve node后续过期的client证书，自动生成的证书Group为system:nodes；

node-server-cert-renewal 自动approve node后续过期的server证书，自动生成的证书Group；

基于安全考虑，CSR approving controllers不会自动approve kubelet server证书签名请求，需要手动approve

kubectl get csr | grep Pending | awk '{print $1}' | xargs kubectl certificate approve

验证

进程验证

#!/bin/bash
source /data/k8s/bin/env.sh
for node_ip in ${NODE_IPS[@]}
do
    echo ">>> ${node_ip}"
    ssh root@${node_ip} "systemctl status kubelet.service|grep -i Active"
done

验证结果：
>>> 192.168.16.104
   Active: active (running) since Fri 2020-01-31 21:59:56 CST; 18h ago
>>> 192.168.16.105
   Active: active (running) since Sun 2019-12-29 19:03:26 CST; 1 months 3 days ago
>>> 192.168.16.106
   Active: active (running) since Sun 2019-12-29 19:03:02 CST; 1 months 3 days ago
>>> 192.168.16.107
   Active: active (running) since Sun 2019-12-29 19:03:04 CST; 1 months 3 days ago

CSR验证

kubectl get csr

刚才处于pending状态的CSR均签发成功。

Node节点状态

[root@master01 ~]# kubectl get node
NAME               STATUS   ROLES    AGE   VERSION
master01.k8s.vip   Ready    <none> 33d   v1.17.0
master02           Ready    <none> 33d   v1.17.0
master03           Ready    <none> 33d   v1.17.0
node01             Ready    <none> 33d   v1.17.0
[root@master01 ~]#

进程端口

#!/bin/bash
source /data/k8s/bin/env.sh
for node_ip in ${NODE_IPS[@]}
do
    echo ">>> ${node_ip}"
    ssh root@${node_ip} "netstat -antp |grep kubelet"
done

结果如下：
>>> 192.168.16.104
tcp 0      0 192.168.16.104:10248     0.0.0.0:* LISTEN 11217/kubelet
tcp 0      0 192.168.16.104:10250     0.0.0.0:* LISTEN 11217/kubelet
tcp 0      0 127.0.0.1:40471         0.0.0.0:* LISTEN 11217/kubelet
tcp 0      0 192.168.16.104:53896     192.168.16.253:8443      ESTABLISHED 11217/kubelet
>>> 192.168.16.105
tcp 0      0 127.0.0.1:43713         0.0.0.0:* LISTEN 28452/kubelet
tcp 0      0 192.168.16.105:10248     0.0.0.0:* LISTEN 28452/kubelet
tcp 0      0 192.168.16.105:10250     0.0.0.0:* LISTEN 28452/kubelet
tcp 0      0 192.168.16.105:59210     192.168.16.253:8443      ESTABLISHED 28452/kubelet
>>> 192.168.16.106
tcp 0      0 127.0.0.1:36795         0.0.0.0:* LISTEN 31918/kubelet
tcp 0      0 192.168.16.106:10248     0.0.0.0:* LISTEN 31918/kubelet
tcp 0      0 192.168.16.106:10250     0.0.0.0:* LISTEN 31918/kubelet
tcp 0      0 192.168.16.106:59192     192.168.16.253:8443      ESTABLISHED 31918/kubelet
>>> 192.168.16.107
tcp 0      0 192.168.16.107:10248     0.0.0.0:* LISTEN 24467/kubelet
tcp 0      0 192.168.16.107:10250     0.0.0.0:* LISTEN 24467/kubelet
tcp 0      0 127.0.0.1:38895         0.0.0.0:* LISTEN 24467/kubelet
tcp 0      0 192.168.16.107:51182     192.168.16.253:8443      ESTABLISHED 24467/kubelet

10248: healthz http 服务；

10250: https 服务，访问该端口时需要认证和授权；

总结

由于集群开启了TLS认证，每个节点上面的kubelet组件都需要使用由kube-apiserver使用的CA签发的有效证书才能与kube-apiserver 通讯；此时如果节点多起来，需要为每个节点单独签署证书将是一件非常繁琐的事情；TLS bootstrapping功能就是让kubelet 先使用一个预定的低权限用户连接到kube-apiserver，发送CSR请求，然后由kube-controller-manager动态签署；

kubelet组件采用主动的查询机制，定期向kube-apiserver获取当前节点应该处理的任务，如果有任务分配到了自己身上（如创建Pod），从而他去处理这些任务；

kubelet暴露了两个端口10248，http形式的healthz服务，另一个是10250，https服务，其实还有一个只读的10255端口，这里是禁用的。