Kubeadm生成的k8s证书内容说明：

证书作用

• 身份验证：Kubernetes使用证书来验证用户或服务的身份。每个用户或服务都可以有自己的证书，用于在与Kubernetes API服务器通信时进行身份验证。这样可以确保只有经过身份验证的用户或服务才能与集群进行交互，增加了集群的安全性。
• 加密通信：Kubernetes使用证书来加密集群内的通信。证书用于生成安全套接字层（SSL）或传输层安全（TLS）连接，确保在集群内部的各个组件之间的通信是加密的。这样可以防止敏感信息在传输过程中被窃取或篡改。
• 集群组件通信：Kubernetes集群中的各个组件（例如API服务器、控制器管理器、调度器等）之间需要进行安全的通信。证书用于生成TLS连接，确保集群组件之间的通信是安全的，以防止未经授权的访问和攻击。
• 服务之间的安全通信：Kubernetes中的服务之间可以通过TLS进行安全通信。每个服务都可以有自己的证书，用于建立安全的通信通道，确保服务之间的通信是加密的和可信的。

证书分组

Kubernetes把证书放在了两个文件夹中

/etc/kubernetes/pki
/etc/kubernetes/pki/etcd

Kubernetes 集群根证书

Kubernetes 集群根证书CA(Kubernetes集群组件的证书签发机构)

/etc/kubernetes/pki/ca.crt
/etc/kubernetes/pki/ca.key

以上这组证书为签发其他Kubernetes组件证书使用的根证书, 可以认为是Kubernetes集群中证书签发机构之一

由此根证书签发的证书有:

kube-apiserver apiserver证书

/etc/kubernetes/pki/apiserver.crt
/etc/kubernetes/pki/apiserver.key

kubelet客户端证书, 用作 kube-apiserver 主动向 kubelet 发起请求时的客户端认证

/etc/kubernetes/pki/apiserver-kubelet-client.crt
/etc/kubernetes/pki/apiserver-kubelet-client.key

kube-apiserver 代理根证书(客户端证书)

用在requestheader-client-ca-file配置选项中, kube-apiserver 使用该证书来验证客户端证书是否为自己所签发

/etc/kubernetes/pki/front-proxy-ca.crt
/etc/kubernetes/pki/front-proxy-ca.key

由此根证书签发的证书只有一组:
代理层(如汇聚层aggregator)使用此套代理证书来向 kube-apiserver 请求认证
代理端使用的客户端证书, 用作代用户与 kube-apiserver 认证

/etc/kubernetes/pki/front-proxy-client.crt
/etc/kubernetes/pki/front-proxy-client.key

etcd 集群根证书

etcd集群所用到的证书都保存在/etc/kubernetes/pki/etcd这路径下, 很明显, 这一套证书是用来专门给etcd集群服务使用的, 设计以下证书文件
etcd 集群根证书CA(etcd 所用到的所有证书的签发机构)

/etc/kubernetes/pki/etcd/ca.crt
/etc/kubernetes/pki/etcd/ca.key

由此根证书签发机构签发的证书有:

• etcd server 持有的服务端证书
• peer 集群中节点互相通信使用的客户端证书
• pod 中定义 Liveness 探针使用的客户端证书
• 配置在 kube-apiserver 中用来与 etcd server 做双向认证的客户端证书

etcd server 持有的服务端证书

/etc/kubernetes/pki/etcd/server.crt
/etc/kubernetes/pki/etcd/server.key

peer 集群中节点互相通信使用的客户端证书

/etc/kubernetes/pki/etcd/peer.crt
/etc/kubernetes/pki/etcd/peer.key

注: Peer：对同一个etcd集群中另外一个Member的称呼

pod 中定义 Liveness 探针使用的客户端证书

kubeadm 部署的 Kubernetes 集群是以 pod 的方式运行 etcd 服务的, 在该 pod 的定义中, 配置了 Liveness 探活探针

/etc/kubernetes/pki/etcd/healthcheck-client.crt
/etc/kubernetes/pki/etcd/healthcheck-client.key

当你 describe etcd 的 pod 时, 会看到如下一行配置:

Liveness: exec [/bin/sh -ec ETCDCTL_API=3 etcdctl --endpoints=https://[127.0.0.1]:2379 --cacert=/etc/kubernetes/pki/etcd/ca.crt --cert=/etc/kubernetes/pki/etcd/healthcheck-client.crt --key=/etc/kubernetes/pki/etcd/healthcheck-client.key get foo] delay=15s timeout=15s period=10s #success=1 #failure=8

配置在 kube-apiserver 中用来与 etcd server 做双向认证的客户端证书

/etc/kubernetes/pki/apiserver-etcd-client.crt
/etc/kubernetes/pki/apiserver-etcd-client.key

延长k8s证书时间

任意一台服务器执行
查看证书有效时间：

openssl x509 -in /etc/kubernetes/pki/ca.crt -noout -text  |grep Not

显示如下，通过下面可看到ca证书有效期是10年，从2023到2033年：

openssl x509 -in /etc/kubernetes/pki/apiserver.crt -noout -text  |grep Not

显示如下，通过下面可看到apiserver证书有效期是1年

延长证书过期时间:

把update-kubeadm-cert.sh文件上传到k8smaster1和k8smaster2节点，在k8smaster1和k8smaster2上执行如下：

#!/bin/bash
#脚本转载自https://github.com/yuyicai/update-kube-cert

set -o errexit
set -o pipefail
# set -o xtrace

log::err() {
  printf "[$(date +'%Y-%m-%dT%H:%M:%S.%N%z')]: \033[31mERROR: \033[0m$@\n"
}

log::info() {
  printf "[$(date +'%Y-%m-%dT%H:%M:%S.%N%z')]: \033[32mINFO: \033[0m$@\n"
}

log::warning() {
  printf "[$(date +'%Y-%m-%dT%H:%M:%S.%N%z')]: \033[33mWARNING: \033[0m$@\n"
}

check_file() {
  if [[ ! -r  ${1} ]]; then
    log::err "can not find ${1}"
    exit 1
  fi
}

# get x509v3 subject alternative name from the old certificate
cert::get_subject_alt_name() {
  local cert=${1}.crt
  check_file "${cert}"
  local alt_name=$(openssl x509 -text -noout -in ${cert} | grep -A1 'Alternative' | tail -n1 | sed 's/[[:space:]]*Address//g')
  printf "${alt_name}\n"
}

# get subject from the old certificate
cert::get_subj() {
  local cert=${1}.crt
  check_file "${cert}"
  local subj=$(openssl x509 -text -noout -in ${cert}  | grep "Subject:" | sed 's/Subject:/\//g;s/\,/\//;s/[[:space:]]//g')
  printf "${subj}\n"
}

cert::backup_file() {
  local file=${1}
  if [[ ! -e ${file}.old-$(date +%Y%m%d) ]]; then
    cp -rp ${file} ${file}.old-$(date +%Y%m%d)
    log::info "backup ${file} to ${file}.old-$(date +%Y%m%d)"
  else
    log::warning "does not backup, ${file}.old-$(date +%Y%m%d) already exists"
  fi
}

# generate certificate whit client, server or peer
# Args:
#   $1 (the name of certificate)
#   $2 (the type of certificate, must be one of client, server, peer)
#   $3 (the subject of certificates)
#   $4 (the validity of certificates) (days)
#   $5 (the x509v3 subject alternative name of certificate when the type of certificate is server or peer)
cert::gen_cert() {
  local cert_name=${1}
  local cert_type=${2}
  local subj=${3}
  local cert_days=${4}
  local alt_name=${5}
  local cert=${cert_name}.crt
  local key=${cert_name}.key
  local csr=${cert_name}.csr
  local csr_conf="distinguished_name = dn\n[dn]\n[v3_ext]\nkeyUsage = critical, digitalSignature, keyEncipherment\n"

  check_file "${key}"
  check_file "${cert}"

  # backup certificate when certificate not in ${kubeconf_arr[@]}
  # kubeconf_arr=("controller-manager.crt" "scheduler.crt" "admin.crt" "kubelet.crt")
  # if [[ ! "${kubeconf_arr[@]}" =~ "${cert##*/}" ]]; then
  #   cert::backup_file "${cert}"
  # fi

  case "${cert_type}" in
    client)
      openssl req -new  -key ${key} -subj "${subj}" -reqexts v3_ext \
        -config <(printf "${csr_conf} extendedKeyUsage = clientAuth\n") -out ${csr}
      openssl x509 -in ${csr} -req -CA ${CA_CERT} -CAkey ${CA_KEY} -CAcreateserial -extensions v3_ext \
        -extfile <(printf "${csr_conf} extendedKeyUsage = clientAuth\n") -days ${cert_days} -out ${cert}
      log::info "generated ${cert}"
    ;;
    server)
      openssl req -new  -key ${key} -subj "${subj}" -reqexts v3_ext \
        -config <(printf "${csr_conf} extendedKeyUsage = serverAuth\nsubjectAltName = ${alt_name}\n") -out ${csr}
      openssl x509 -in ${csr} -req -CA ${CA_CERT} -CAkey ${CA_KEY} -CAcreateserial -extensions v3_ext \
        -extfile <(printf "${csr_conf} extendedKeyUsage = serverAuth\nsubjectAltName = ${alt_name}\n") -days ${cert_days} -out ${cert}
      log::info "generated ${cert}"
    ;;
    peer)
      openssl req -new  -key ${key} -subj "${subj}" -reqexts v3_ext \
        -config <(printf "${csr_conf} extendedKeyUsage = serverAuth, clientAuth\nsubjectAltName = ${alt_name}\n") -out ${csr}
      openssl x509 -in ${csr} -req -CA ${CA_CERT} -CAkey ${CA_KEY} -CAcreateserial -extensions v3_ext \
        -extfile <(printf "${csr_conf} extendedKeyUsage = serverAuth, clientAuth\nsubjectAltName = ${alt_name}\n") -days ${cert_days} -out ${cert}
      log::info "generated ${cert}"
    ;;
    *)
      log::err "unknow, unsupported etcd certs type: ${cert_type}, supported type: client, server, peer"
      exit 1
  esac

  rm -f ${csr}
}

cert::update_kubeconf() {
  local cert_name=${1}
  local kubeconf_file=${cert_name}.conf
  local cert=${cert_name}.crt
  local key=${cert_name}.key

  # generate  certificate
  check_file ${kubeconf_file}
  # get the key from the old kubeconf
  grep "client-key-data" ${kubeconf_file} | awk {'print$2'} | base64 -d > ${key}
  # get the old certificate from the old kubeconf
  grep "client-certificate-data" ${kubeconf_file} | awk {'print$2'} | base64 -d > ${cert}
  # get subject from the old certificate
  local subj=$(cert::get_subj ${cert_name})
  cert::gen_cert "${cert_name}" "client" "${subj}" "${CAER_DAYS}"
  # get certificate base64 code
  local cert_base64=$(base64 -w 0 ${cert})

  # backup kubeconf
  # cert::backup_file "${kubeconf_file}"

  # set certificate base64 code to kubeconf
  sed -i 's/client-certificate-data:.*/client-certificate-data: '${cert_base64}'/g' ${kubeconf_file}

  log::info "generated new ${kubeconf_file}"
  rm -f ${cert}
  rm -f ${key}

  # set config for kubectl
  if [[ ${cert_name##*/} == "admin" ]]; then
    mkdir -p ~/.kube
    cp -fp ${kubeconf_file} ~/.kube/config
    log::info "copy the admin.conf to ~/.kube/config for kubectl"
  fi
}

cert::update_etcd_cert() {
  PKI_PATH=${KUBE_PATH}/pki/etcd
  CA_CERT=${PKI_PATH}/ca.crt
  CA_KEY=${PKI_PATH}/ca.key

  check_file "${CA_CERT}"
  check_file "${CA_KEY}"

  # generate etcd server certificate
  # /etc/kubernetes/pki/etcd/server
  CART_NAME=${PKI_PATH}/server
  subject_alt_name=$(cert::get_subject_alt_name ${CART_NAME})
  cert::gen_cert "${CART_NAME}" "peer" "/CN=etcd-server" "${CAER_DAYS}" "${subject_alt_name}"

  # generate etcd peer certificate
  # /etc/kubernetes/pki/etcd/peer
  CART_NAME=${PKI_PATH}/peer
  subject_alt_name=$(cert::get_subject_alt_name ${CART_NAME})
  cert::gen_cert "${CART_NAME}" "peer" "/CN=etcd-peer" "${CAER_DAYS}" "${subject_alt_name}"

  # generate etcd healthcheck-client certificate
  # /etc/kubernetes/pki/etcd/healthcheck-client
  CART_NAME=${PKI_PATH}/healthcheck-client
  cert::gen_cert "${CART_NAME}" "client" "/O=system:masters/CN=kube-etcd-healthcheck-client" "${CAER_DAYS}"

  # generate apiserver-etcd-client certificate
  # /etc/kubernetes/pki/apiserver-etcd-client
  check_file "${CA_CERT}"
  check_file "${CA_KEY}"
  PKI_PATH=${KUBE_PATH}/pki
  CART_NAME=${PKI_PATH}/apiserver-etcd-client
  cert::gen_cert "${CART_NAME}" "client" "/O=system:masters/CN=kube-apiserver-etcd-client" "${CAER_DAYS}"

  # restart etcd
  docker ps | awk '/k8s_etcd/{print$1}' | xargs -r -I '{}' docker restart {} || true
  log::info "restarted etcd"
}

cert::update_master_cert() {
  PKI_PATH=${KUBE_PATH}/pki
  CA_CERT=${PKI_PATH}/ca.crt
  CA_KEY=${PKI_PATH}/ca.key

  check_file "${CA_CERT}"
  check_file "${CA_KEY}"

  # generate apiserver server certificate
  # /etc/kubernetes/pki/apiserver
  CART_NAME=${PKI_PATH}/apiserver
  subject_alt_name=$(cert::get_subject_alt_name ${CART_NAME})
  cert::gen_cert "${CART_NAME}" "server" "/CN=kube-apiserver" "${CAER_DAYS}" "${subject_alt_name}"

  # generate apiserver-kubelet-client certificate
  # /etc/kubernetes/pki/apiserver-kubelet-client
  CART_NAME=${PKI_PATH}/apiserver-kubelet-client
  cert::gen_cert "${CART_NAME}" "client" "/O=system:masters/CN=kube-apiserver-kubelet-client" "${CAER_DAYS}"

  # generate kubeconf for controller-manager,scheduler,kubectl and kubelet
  # /etc/kubernetes/controller-manager,scheduler,admin,kubelet.conf
  cert::update_kubeconf "${KUBE_PATH}/controller-manager"
  cert::update_kubeconf "${KUBE_PATH}/scheduler"
  cert::update_kubeconf "${KUBE_PATH}/admin"
  # check kubelet.conf
  # https://github.com/kubernetes/kubeadm/issues/1753
  set +e
  grep kubelet-client-current.pem /etc/kubernetes/kubelet.conf > /dev/null 2>&1
  kubelet_cert_auto_update=$?
  set -e
  if [[ "$kubelet_cert_auto_update" == "0" ]]; then
    log::warning "does not need to update kubelet.conf"
  else
    cert::update_kubeconf "${KUBE_PATH}/kubelet"
  fi

  # generate front-proxy-client certificate
  # use front-proxy-client ca
  CA_CERT=${PKI_PATH}/front-proxy-ca.crt
  CA_KEY=${PKI_PATH}/front-proxy-ca.key
  check_file "${CA_CERT}"
  check_file "${CA_KEY}"
  CART_NAME=${PKI_PATH}/front-proxy-client
  cert::gen_cert "${CART_NAME}" "client" "/CN=front-proxy-client" "${CAER_DAYS}"

  # restart apiserve, controller-manager, scheduler and kubelet
  docker ps | awk '/k8s_kube-apiserver/{print$1}' | xargs -r -I '{}' docker restart {} || true
  log::info "restarted kube-apiserver"
  docker ps | awk '/k8s_kube-controller-manager/{print$1}' | xargs -r -I '{}' docker restart {} || true
  log::info "restarted kube-controller-manager"
  docker ps | awk '/k8s_kube-scheduler/{print$1}' | xargs -r -I '{}' docker restart {} || true
  log::info "restarted kube-scheduler"
  systemctl restart kubelet
  log::info "restarted kubelet"
}

main() {
  local node_tpye=$1
  
  KUBE_PATH=/etc/kubernetes
  CAER_DAYS=3650

  # backup $KUBE_PATH to $KUBE_PATH.old-$(date +%Y%m%d)
  cert::backup_file "${KUBE_PATH}"

  case ${node_tpye} in
    etcd)
	  # update etcd certificates
      cert::update_etcd_cert
    ;;
    master)
	  # update master certificates and kubeconf
      cert::update_master_cert
    ;;
    all)
      # update etcd certificates
      cert::update_etcd_cert
      # update master certificates and kubeconf
      cert::update_master_cert
    ;;
    *)
      log::err "unknow, unsupported certs type: ${cert_type}, supported type: all, etcd, master"
      printf "Documentation: https://github.com/yuyicai/update-kube-cert
  example:
    '\033[32m./update-kubeadm-cert.sh all\033[0m' update all etcd certificates, master certificates and kubeconf
      /etc/kubernetes
      ├── admin.conf
      ├── controller-manager.conf
      ├── scheduler.conf
      ├── kubelet.conf
      └── pki
          ├── apiserver.crt
          ├── apiserver-etcd-client.crt
          ├── apiserver-kubelet-client.crt
          ├── front-proxy-client.crt
          └── etcd
              ├── healthcheck-client.crt
              ├── peer.crt
              └── server.crt

    '\033[32m./update-kubeadm-cert.sh etcd\033[0m' update only etcd certificates
      /etc/kubernetes
      └── pki
          ├── apiserver-etcd-client.crt
          └── etcd
              ├── healthcheck-client.crt
              ├── peer.crt
              └── server.crt

    '\033[32m./update-kubeadm-cert.sh master\033[0m' update only master certificates and kubeconf
      /etc/kubernetes
      ├── admin.conf
      ├── controller-manager.conf
      ├── scheduler.conf
      ├── kubelet.conf
      └── pki
          ├── apiserver.crt
          ├── apiserver-kubelet-client.crt
          └── front-proxy-client.crt
"
      exit 1
    esac
}

main "$@"

chmod +x update-kubeadm-cert.sh

执行下面命令，修改证书过期时间，把时间延长到10年

./update-kubeadm-cert.sh all

在k8smaster1节点查询Pod是否正常,能查询出数据说明证书签发完成

kubectl  get pods -n kube-system
#显示如下，能够看到pod信息，说明证书签发正常：

openssl x509 -in /etc/kubernetes/pki/ca.crt -noout -text  |grep Not

openssl x509 -in /etc/kubernetes/pki/apiserver.crt -noout -text  |grep Not

显示如下，通过下面可看到apiserver证书有效期是10年，从2023到2033年：