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keepalived-高可用集群.md
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keepalived-高可用集群.md
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<h2><center>keepalived 高可用集群</center></h2>
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------
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## 一：keepalived 简介
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### 1. 简介
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`keepalived`是集群管理中保证集群高可用`(HA)`的一个服务软件，其功能类似于`heartbeat`，用来防止单点故障。
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### 2. 工作原理
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`keepalived`是以`VRRP`协议为实现基础的，当`backup`收不到`vrrp`包时就认为`master`宕掉了，这时就需要根据`VRRP`的优先级来选举一个`backup`当`master`。这样我们就可以保证集群的高可用。
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`keepalived`是以`VRRP`协议为实现基础的，`VRRP`全称`Virtual Router Redundancy Protocol`，即虚拟路由冗余协议。
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虚拟路由冗余协议，可以认为是实现路由器高可用的协议，即将`N`台提供相同功能的路由器组成一个路由器组，这个组里面有一个`master`和多个`backup`，`master`上面有一个对外提供服务的`vip`（该路由器所在局域网内其他机器的默认路由为该vip），`master`会发组播，当`backup`收不到`vrrp`包时就认为`master`宕掉了，这时就需要根据`VRRP`的优先级来选举一个`backup`当`master`。这样的话就可以保证路由器的高可用了。
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`keepalived`主要有三个模块，分别是`core`、`check`和`vrrp`。`core`模块为`keepalived`的核心，负责主进程的启动、维护以及全局配置文件的加载和解析。`check`负责健康检查，包括常见的各种检查方式。`vrrp`模块是来实现`VRRP`协议的。
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### 3. 什么是脑裂
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脑裂`（split-brain）`：指在一个高可用`（HA）`系统中，当联系着的两个节点断开联系时，本来为一个整体的系统，分裂为两个独立节点，这时两个节点开始争抢共享资源，结果会导致系统混乱，数据损坏。
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对于无状态服务的`HA`，无所谓脑裂不脑裂；但对有状态服务(比如`MySQL`)的`HA`，必须要严格防止脑裂。
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究竟是有状态服务，还是无状态服务，其判断依据——两个来自相同发起者的请求在服务器端是否具备上下文关系。
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脑裂：`backup`强资源，`master`不认为自己会死，他俩抢着为客户端服务。
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解决方案：shoot the other in the head 爆头 master
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注意：在商城里购买一件商品。需要经过放入购物车、确认订单、付款等多个步骤。由于`HTTP`协议本身是无状态的，所以为了实现有状态服务，就需要通过一些额外的方案。比如最常见的`session`，将用户挑选的商品（购物车），保存到`session`中，当付款的时候，再从购物车里取出商品信息。
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## 二：LVS + Keepalived
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### 1. 环境准备
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| 服务器 | IP | VIP | 说明 |
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| ------------- | --------------- | --------------------- | ---------- |
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| master | 192.168.159.131 | | 主节点 |
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| backup | 192.168.159.132 | | 备用节点 |
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| real server 1 | 192.168.159.133 | lo:0：192.168.159.100 | 真实服务器 |
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| real server 2 | 192.168.159.134 | lo:0：192.168.159.100 | 真实服务器 |
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### 2. director server 部署
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**安装keepalived、ipvsadm**
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```bash
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[root@master/backup ~]# yum -y install keepalived ipvsadm
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```
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**修改配置文件**
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```bash
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master：
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[root@master ~]# vim /etc/keepalived/keepalived.conf
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global_defs {
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router_id LVS_MASTER
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}
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vrrp_instance VI_1 {
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state MASTER
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interface ens33 // 网卡名称，根据实际情况修改
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virtual_router_id 51 // 主备必须一致
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priority 100 // 定义优先级
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advert_int 1 // 设定master与backup负载均衡器之间同步检查的时间间隔，单位是秒
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authentication {
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auth_type PASS // 主要有PASS和AH两种
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auth_pass 1111 // 主备密码一致
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}
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virtual_ipaddress {
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192.168.159.100 // 虚拟IP（VIP）
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}
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}
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virtual_server 192.168.159.100 80 {
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delay_loop 6 // 健康检查时间间隔
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lb_algo rr
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lb_kind DR
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#persistence_timeout 50 // 设置会话保持时间，对动态网页非常有用
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protocol TCP // 指定转发协议类型，有TCP和UDP两种
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real_server 192.168.159.133 80 {
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weight 1
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TCP_CHECK {
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connect_timeout 3 // 连接超时
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retry 3 // 重连次数
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delay_before_retry 3 // 重试间隔
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}
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}
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real_server 192.168.159.134 80 {
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weight 1
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TCP_CHECK {
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connnect_timeout 3
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retry 3
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delay_before_retry 3
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}
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}
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}
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backup:
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[root@backup ~]# vim /etc/keepalived/keepalived.conf
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global_defs {
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router_id LVS_BACKUP
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}
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vrrp_instance VI_1 {
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state BACKUP
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interface ens33
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virtual_router_id 51
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priority 90
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advert_int 1
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authentication {
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auth_type PASS
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auth_pass 1111
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}
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virtual_ipaddress {
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192.168.159.100
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}
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}
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virtual_server 192.168.159.100 80 {
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delay_loop 6
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lb_algo rr
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lb_kind DR
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#persistence_timeout 50
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protocol TCP
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real_server 192.168.159.133 80 {
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weight 1
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TCP_CHECK {
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connect_timeout 3
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retry 3
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delay_before_retry 3
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}
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}
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real_server 192.168.159.134 80 {
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weight 1
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TCP_CHECK {
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connect_timeout 3
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retry 3
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delay_before_retry 3
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}
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}
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}
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```
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### 3. real server 配置
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**安装httpd**
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```bash
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[root@real-server1/2 ~]# yum -y install httpd
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```
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**设置测试网页**
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```bash
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[root@real-server1/2 ~]# echo "Real Server 1/2" > /var/www/html/index.html
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```
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**启动服务**
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```bash
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[root@real-server1/2 ~]# systemctl start httpd
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[root@real-server1/2 ~]# systemctl enable httpd
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```
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**配置 ARP 抑制**
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```bash
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[root@real-server1/2 ~]# vim /etc/sysctl.conf
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net.ipv4.conf.all.arp_ignore = 1
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net.ipv4.conf.all.arp_announce = 2
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net.ipv4.conf.lo.arp_ignore = 1
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net.ipv4.conf.lo.arp_announce = 2
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查看：
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[root@real-server1/2 ~]# sysctl -p
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```
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**添加 VIP 到 lo 接口**
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```bash
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[root@real-server1/2 ~]# echo 'DEVICE=lo:0 IPADDR=192.168.159.100 NETMASK=255.255.255.255 ONBOOT=yes' > /etc/sysconfig/network-scripts/ifcfg-lo:0
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[root@real-server1/2 ~]# ifup lo:0
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```
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### 4. 启动 keepalived
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```bash
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[root@master/backup ~]# systemctl start keepalived
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[root@master/backup ~]# systemctl enable keepalived
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```
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### 5. 检测
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**其他服务器查看**
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```bash
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[root@wxin ~]# for i in {1..10}; do
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> curl http://192.168.159.100
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> done
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Real Server 2
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Real Server 1
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Real Server 2
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Real Server 1
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Real Server 2
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Real Server 1
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Real Server 2
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Real Server 1
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Real Server 2
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Real Server 1
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```
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**主节点**
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```bash
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查看IP
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[root@master ~]# ip addr show ens33
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2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
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link/ether 00:0c:29:ba:8f:62 brd ff:ff:ff:ff:ff:ff
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inet 192.168.159.131/24 brd 192.168.159.255 scope global noprefixroute ens33
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valid_lft forever preferred_lft forever
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inet 192.168.159.100/32 scope global ens33 # 主节点存在，备节点不存在
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valid_lft forever preferred_lft forever
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inet6 fe80::9e8b:2599:99f6:4087/64 scope link noprefixroute
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valid_lft forever preferred_lft forever
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[root@backup ~]# ip addr show ens33
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2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
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link/ether 00:0c:29:1a:96:29 brd ff:ff:ff:ff:ff:ff
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inet 192.168.159.132/24 brd 192.168.159.255 scope global noprefixroute ens33
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valid_lft forever preferred_lft forever
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inet6 fe80::e859:ecb:5e5:4b9a/64 scope link tentative noprefixroute dadfailed
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valid_lft forever preferred_lft forever
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inet6 fe80::9e8b:2599:99f6:4087/64 scope link tentative noprefixroute dadfailed
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valid_lft forever preferred_lft forever
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inet6 fe80::32c3:53e0:5709:d314/64 scope link tentative noprefixroute dadfailed
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valid_lft forever preferred_lft forever
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```
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**主节点宕机后**
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```bash
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[root@master ~]# systemctl stop keepalived
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[root@master ~]# ip addr show ens33
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2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
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link/ether 00:0c:29:ba:8f:62 brd ff:ff:ff:ff:ff:ff
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inet 192.168.159.131/24 brd 192.168.159.255 scope global noprefixroute ens33
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valid_lft forever preferred_lft forever
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inet6 fe80::9e8b:2599:99f6:4087/64 scope link noprefixroute
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valid_lft forever preferred_lft forever
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VIP 转移到backup后
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[root@backup ~]# ip addr show ens33
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2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
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link/ether 00:0c:29:1a:96:29 brd ff:ff:ff:ff:ff:ff
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inet 192.168.159.132/24 brd 192.168.159.255 scope global noprefixroute ens33
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valid_lft forever preferred_lft forever
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inet 192.168.159.100/32 scope global ens33
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valid_lft forever preferred_lft forever
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inet6 fe80::e859:ecb:5e5:4b9a/64 scope link tentative noprefixroute dadfailed
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valid_lft forever preferred_lft forever
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inet6 fe80::9e8b:2599:99f6:4087/64 scope link tentative noprefixroute dadfailed
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valid_lft forever preferred_lft forever
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inet6 fe80::32c3:53e0:5709:d314/64 scope link tentative noprefixroute dadfailed
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valid_lft forever preferred_lft forever
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```
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