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<h1><center>高可用集群</center></h1>
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作者：行癫（盗版必究）
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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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如何判断谁是master：看vip，vip在谁上谁就是master
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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：
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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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#### 2.项目部署
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主/备调度器安装软件
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```shell
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[root@lvs-keepalived-master ~]# yum -y install ipvsadm keepalived
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[root@lvs-keepalived-slave ~]# yum -y install ipvsadm keepalived
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```
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主/备调度器配置
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```shell
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lvs-master：
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[root@ha-proxy-master ~]# vim /etc/keepalived/keepalived.conf
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! Configuration File for keepalived
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global_defs {
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router_id lvs-keepalived-master #辅助改为lvs-backup
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}
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vrrp_instance VI_1 {
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state MASTER
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interface ens33 #VIP绑定接口
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virtual_router_id 80 #VRID 同一组集群，主备一致
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priority 100 #本节点优先级，辅助改为50
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advert_int 1 #检查间隔，默认为1s
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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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192.168.246.160/24
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}
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}
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virtual_server 192.168.246.160 80 { #LVS配置
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delay_loop 3
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lb_algo rr #LVS调度算法
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lb_kind DR #LVS集群模式（路由模式）
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nat_mask 255.255.255.0
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protocol TCP #健康检查使用的协议
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real_server 192.168.246.162 80 {
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weight 1
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inhibit_on_failure #当该节点失败时，把权重设置为0，而不是从IPVS中删除
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TCP_CHECK { #健康检查
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connect_port 80 #检查的端口
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connect_timeout 3 #连接超时的时间
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}
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}
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real_server 192.168.246.163 80 {
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weight 1
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inhibit_on_failure
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TCP_CHECK {
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connect_timeout 3
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connect_port 80
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}
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}
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}
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[root@lvs-keepalived-slave ~]# vim /etc/keepalived/keepalived.conf
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! Configuration File for keepalived
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global_defs {
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router_id lvs-keepalived-slave
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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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nopreempt #不抢占资源
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virtual_router_id 80
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priority 50
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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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192.168.246.160/24
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}
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}
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virtual_server 192.168.246.160 80 {
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delay_loop 3
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lb_algo rr
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lb_kind DR
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nat_mask 255.255.255.0
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persistence_timeout 20
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protocol TCP
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real_server 192.168.246.162 80 {
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weight 1
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inhibit_on_failure
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TCP_CHECK {
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connect_port 80
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connect_timeout 3
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}
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}
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real_server 192.168.246.163 80 {
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weight 1
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inhibit_on_failure
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TCP_CHECK {
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connect_timeout 3
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connect_port 80
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}
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}
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}
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```
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#### 3.LVS部署
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```shell
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[root@lvs-server ~]# ip addr add dev ens33 192.168.246.160/32 #设置VIP
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[root@xingdian-cloud ~]# ipvsadm -S > /etc/sysconfig/ipvsadm
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[root@xingdian-cloud ~]# systemctl start ipvsadm
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[root@lvs-server ~]# ipvsadm -A -t 192.168.246.160:80 -s rr
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[root@lvs-server ~]# ipvsadm -a -t 192.168.246.160:80 -r 192.168.246.163 -g
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[root@lvs-server ~]# ipvsadm -a -t 192.168.246.160:80 -r 192.168.246.162 -g
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[root@lvs-keepalived-master ~]# ipvsadm -Ln
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IP Virtual Server version 1.2.1 (size=4096)
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Prot LocalAddress:Port Scheduler Flags
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-> RemoteAddress:Port Forward Weight ActiveConn InActConn
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TCP 192.168.246.160:80 rr persistent 20
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-> 192.168.246.162:80 Route 1 0 0
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-> 192.168.246.163:80 Route 0 0 0
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```
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#### 4.启动KeepAlived
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```shell
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[root@lvs-keepalived-master ~]# systemctl start keepalived
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[root@lvs-keepalived-master ~]# systemctl enable keepalived
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```
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#### 5.RS配置
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```
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[root@test-nginx1 ~]# yum install -y nginx
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[root@test-nginx2 ~]# yum install -y nginx
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[root@test-nginx1 ~]# ip addr add dev lo 192.168.246.160/32
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[root@test-nginx1 ~]# echo "net.ipv4.conf.all.arp_ignore = 1" >> /etc/sysctl.conf
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[root@test-nginx1 ~]# echo 2 > /proc/sys/net/ipv4/conf/all/arp_announce
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[root@test-nginx1 ~]# sysctl -p
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[root@test-nginx1 ~]# echo "web1..." >> /usr/share/nginx/html/index.html
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[root@test-nginx1 ~]# systemctl start nginx
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```
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## 三：LVS+Nginx
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```shell
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1.准备好web-server（两台都要做）
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web-server-1：10.0.0.42
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web-server-2：10.0.0.141
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安装nginx，并且保证nginx正常运行
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分别要在web-server上创建一个测试界面
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echo "web-server-1" > /usr/share/nginx/html/index.html
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echo "web-server-2" > /usr/share/nginx/html/index.html
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检测web-server是否正常被访问
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2.负载均衡的部署（两台都要做）
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master：10.0.0.154
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backup：10.0.0.27
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master和backup都要做以下操作：
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vim /etc/nginx/nginx.conf 添加以下内容
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upstream xingdian {
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server 10.0.0.42:80;
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server 10.0.0.141:80;
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}
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vim /etc/nginx/conf.d/default.conf 修改一下内容
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location / {
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proxy_pass http://xingdian;
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proxy_redirect default;
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proxy_set_header Host $http_host;
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proxy_set_header X-Real-IP $remote_addr;
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proxy_set_header REMOTE-HOST $remote_addr;
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proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
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}
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保证nginx的负载均衡可用，客户端可以访问测试：
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Keepalived实现调度器HA（vip我们直接写在配置文件中）
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1. 主/备调度器安装软件（安装keepalived）
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[root@master ~]# yum install -y keepalived
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[root@backup ~]# yum install -y keepalived
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[root@master ~]# cp /etc/keepalived/keepalived.conf /etc/keepalived/keepalived.conf.bak （略）
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[root@nginx-proxy-master ~]# vim /etc/keepalived/keepalived.conf
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! Configuration File for keepalived
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global_defs {
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router_id director1 #辅助改为director2
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}
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vrrp_instance VI_1 {
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state MASTER #定义主还是备
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interface ens33 #VIP绑定接口
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virtual_router_id 80 #整个集群的调度器一致
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priority 100 #back改为50
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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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10.0.0.110/24
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}
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}
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[root@backup ~]# cp /etc/keepalived/keepalived.conf /etc/keepalived/keepalived.conf.bak
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[root@backup ~]# vim /etc/keepalived/keepalived.conf
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! Configuration File for keepalived
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global_defs {
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router_id directory2
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}
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vrrp_instance VI_1 { #实例名称，两台要保持相同
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state BACKUP #设置为backup
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interface ens33 #心跳网卡
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nopreempt #设置到back上面，不抢占资源
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virtual_router_id 80 #虚拟路由编号，主备要保持一致
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priority 50 #辅助改为50
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advert_int 1 #检查间隔，单位秒
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authentication { 秘钥认证
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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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10.0.0.110/24
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}
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}
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3. 启动KeepAlived（主备均启动）
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[root@master ~]# systemctl enable keepalived
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[root@master ~]# systemctl start keepalived
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```
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## 四：健康检测
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```shell
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#!/bin/bash
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#+检查nginx进程是否存在
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counter=$(ps -C httpd --no-heading|wc -l) #此行有服务名
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if [ "${counter}" = "0" ]; then
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#尝试启动一次nginx，停止5秒后再次检测
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service httpd start #启动服务
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sleep 5
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counter=$(ps -C httpd --no-heading|wc -l) #此行有服务名
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if [ "${counter}" = "0" ]; then
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#如果启动没成功，就杀掉keepalive触发主备切换
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service keepalived stop
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fi
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fi
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```
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