集群介绍

• 根据功能划分为两大类：高可用和负载均衡
• 高可用集群通常为两台服务器，一台工作，另外一台作为冗余，当提供服务的机器宕机，冗余将接替继续提供服务
• 业内有个综合评分比如4个九，甚至5个九六个九来衡量服务的高可用，一般大企业的核心业务都有高可用，如果一个机器故障，一分钟之内就可以切换到另一台上
• 实现高可用的开源软件有：heartbeat、keepalived
• 负载均衡集群，需要有一台服务器作为分发器，它负责把用户的请求分发给后端的服务器处理，在这个集群里，除了分发器外，就是给用户提供服务的服务器了，这些服务器数量至少为2
• 实现负载均衡的开源软件有LVS、keepalived、haproxy、nginx，商业的有F5、Netscaler
  

  keepalived介绍

• 在这里我们使用keepalived来实现高可用集群，因为heartbeat在centos6上有一些问题，影响实验效果，并更新不及时
• keepalived通过VRRP（Virtual Router Redundancy Protocl即虚拟路由冗余协议）来实现高可用。
• 在这个协议里会将多台功能相同的路由器（其实是一台机器）组成一个小组，这个小组里会有1个master角色和N（N>=1）个backup角色。
• master会通过组播的形式向各个backup发送VRRP协议的数据包，当backup收不到master发来的VRRP数据包时，就会认为master宕机了。此时就需要根据各个backup的优先级来决定谁成为新的mater。
• Keepalived要有三个模块，分别是core、check和vrrp。其中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模块负责健康检查，vrrp模块是来实现VRRP协议的。
  

  用keepalived配置高可用集群

• 准备两台机器130和132，130作为master，132作为backup
• 两台机器都执行yum install -y keepalived
• 两台机器都安装nginx，其中130上已经编译安装过nginx，132上需要yum安装nginx: yum install -y nginx
  • 之所以选择nginx，在生产环境中，好多企业把它作为负载均衡器，如果它挂掉，影响后面好多web服务器，所以不能出现单点故障
• 编辑130上的keepalived配置文件，

  [[email protected] ~]# > /etc/keepalived/keepalived.conf
  [[email protected] ~]# vim !$
  vim /etc/keepalived/keepalived.conf
  global_defs {                      #这个全局定义参数
  notification_email {            #出现问题给邮箱发邮件，
   [email protected]
  }
  notification_email_from [email protected] #由哪一个邮件发送
  smtp_server 127.0.0.1
  smtp_connect_timeout 30
  router_id LVS_DEVEL
  }
  vrrp_script chk_nginx {        #检测一个服务是否正常，需要有个脚本
  script "/usr/local/sbin/check_ng.sh"
  interval 3   # 3秒检测一次
  }
  vrrp_instance VI_1 {   # 定义master相关的
  state MASTER       #如果是从就是backup
  interface ens33    #定义网卡
  virtual_router_id 51  # 定义路由器的id
  priority 100          #定义权重
  advert_int 1
  authentication {        #认证相关
      auth_type PASS
      auth_pass aminglinux>com
  }
  virtual_ipaddress {   #定义vip（公有的ip）
      192.168.21.100
  }
  track_script {    #加载服务
      chk_nginx
  }
  }

• 在130上编辑监控脚本

  [[email protected] ~]# vim /usr/local/sbin/check_ng.sh
  #!/bin/bash
  #时间变量，用于记录日志
  d=`date --date today +%Y%m%d_%H:%M:%S`
  #计算nginx进程数量
  n=`ps -C nginx --no-heading|wc -l`
  #如果进程为0，则启动nginx，并且再次检测nginx进程数量，
  #如果还为0，说明nginx无法启动，此时需要关闭keepalived(防止脑裂)
  if [ $n -eq "0" ]; then
      /etc/init.d/nginx start
      n2=`ps -C nginx --no-heading|wc -l`
      if [ $n2 -eq "0"  ]; then
              echo "$d nginx down,keepalived will stop" >> /var/log/check_ng.log
              systemctl stop keepalived
      fi
  fi

• 给脚本755权限，并启动keepalived服务

  [[email protected] ~]# chmod 755 /usr/local/sbin/check_ng.sh
  [[email protected] ~]# systemctl start keepalived
  [[email protected] ~]# ps aux |grep keepa
  root      2895  0.0  0.0 118608  1388 ?        Ss   23:20   0:00 /usr/sbin/keepalived -D
  root      2896  0.1  0.1 127468  3304 ?        S    23:20   0:00 /usr/sbin/keepalived -D
  root      2899  0.3  0.1 127408  2836 ?        S    23:20   0:00 /usr/sbin/keepalived -D
  root      2961  0.0  0.0 112676   980 pts/1    S+   23:20   0:00 grep --color=auto keepa

• 检测下nginx可以自动加载不

  [[email protected] ~]# ps aux |grep nginx
  root      1016  0.0  0.0  46008  1260 ?        Ss   20:52   0:00 nginx: master process /usr/localnginx/sbin/nginx -c /usr/local/nginx/conf/nginx.conf
  nobody    1017  0.0  0.2  48496  4152 ?        S    20:52   0:00 nginx: worker process
  nobody    1018  0.0  0.2  48496  3896 ?        S    20:52   0:00 nginx: worker process
  root      2982  0.0  0.0 112680   980 pts/1    S+   23:20   0:00 grep --color=auto nginx
  [[email protected] ~]# /etc/init.d/nginx stop
  Stopping nginx (via systemctl):                            [  确定  ]
  [[email protected] ~]# ps aux |grep nginx
  root      3266  1.0  0.0  46008  1252 ?        Ss   23:22   0:00 nginx: master process /usr/localnginx/sbin/nginx -c /usr/local/nginx/conf/nginx.conf
  nobody    3267  0.0  0.2  48496  3892 ?        S    23:22   0:00 nginx: worker process
  nobody    3268  0.0  0.2  48496  3892 ?        S    23:22   0:00 nginx: worker process
  root      3273  0.0  0.0 112676   984 pts/1    S+   23:22   0:00 grep --color=auto nginx

• 日志

  [[email protected] ~]# less /var/log/messages

• 查看vip

  [[email protected] ~]# ip add
  1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1
  link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
  inet 127.0.0.1/8 scope host lo
     valid_lft forever preferred_lft forever
  inet6 ::1/128 scope host
     valid_lft forever preferred_lft forever
  2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
  link/ether 00:0c:29:87:fb:87 brd ff:ff:ff:ff:ff:ff
  inet 192.168.21.128/24 brd 192.168.21.255 scope global ens33
     valid_lft forever preferred_lft forever
  inet 192.168.21.100/32 scope global ens33
     valid_lft forever preferred_lft forever
  inet6 fe80::68fd:e6fa:c781:f5a6/64 scope link
     valid_lft forever preferred_lft forever
  3: ens37: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
  link/ether 00:0c:29:87:fb:91 brd ff:ff:ff:ff:ff:ff
  inet 192.168.110.136/24 brd 192.168.110.255 scope global dynamic ens37
     valid_lft 1278sec preferred_lft 1278sec
  inet6 fe80::c559:4a92:72f1:b448/64 scope link
     valid_lft forever preferred_lft forever

• 132上编辑配置文件

  [[email protected] ~]# > /etc/keepalived/keepalived.conf
  [[email protected] ~]# vim /etc/keepalived/keepalived.conf
  global_defs {
  notification_email {
   [email protected]
  }
  notification_email_from [email protected]
  smtp_server 127.0.0.1
  smtp_connect_timeout 30
  router_id LVS_DEVEL
  }
  vrrp_script chk_nginx {
  script "/usr/local/sbin/check_ng.sh"
  interval 3
  }
  vrrp_instance VI_1 {
  state BACKUP
  interface ens33
  virtual_router_id 51
  priority 90
  advert_int 1
  authentication {
      auth_type PASS
      auth_pass aminglinux>com
  }
  virtual_ipaddress {
      192.168.21.100
  }
  
  track_script {
      chk_nginx
  }
  }

• 132上编辑监控脚本

  [[email protected] ~]# vim /usr/local/sbin/check_ng.sh
  #时间变量，用于记录日志
  d=`date --date today +%Y%m%d_%H:%M:%S`
  #计算nginx进程数量
  n=`ps -C nginx --no-heading|wc -l`
  #如果进程为0，则启动nginx，并且再次检测nginx进程数量，
  #如果还为0，说明nginx无法启动，此时需要关闭keepalived
  if [ $n -eq "0" ]; then
      systemctl start nginx
      n2=`ps -C nginx --no-heading|wc -l`
      if [ $n2 -eq "0"  ]; then
              echo "$d nginx down,keepalived will stop" >> /var/log/check_ng.log
              systemctl stop keepalived
      fi
  fi

• 给脚本755权限并启动keepalived

  [[email protected] ~]# chmod 755 /usr/local/sbin/check_ng.sh
  [[email protected] ~]# systemctl start keepalived

  测试

• curl或者浏览器打开

  [[email protected] ~]# curl [email protected]
  master,master.
  [[email protected] ~]# curl  [email protected]
  backup,backup.
  [[email protected] ~]# curl  [email protected]
  master,master.

• 测试高可用

  [[email protected] ~]# systemctl stop keepalived
  [[email protected] ~]# curl [email protected]
  backup,backup.
  [[email protected] ~]# systemctl start  keepalived
  [[email protected] ~]# curl [email protected]
  master,master.

  扩展

• heartbeat和keepalived比较
• DRBD工作原理和配置
• mysql+keepalived

原文地址：http://blog.51cto.com/akui2521/2135810