keepalived高可用

keepalived是什么
    keepalived是集群管理中保证集群高可用的一个服务软件，用来防止单点故障。

keepalived工作原理
    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。

    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。

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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脑裂  split barin：
Keepalived的BACKUP主机在收到不MASTER主机报文后就会切换成为master，如果是它们之间的通信线路出现问题，无法接收到彼此的组播通知，但是两个节点实际都处于正常工作状态，这时两个节点均为master强行绑定虚拟IP，导致不可预料的后果，这就是脑裂。
解决方式:
1、添加更多的检测手段，比如冗余的心跳线（两块网卡做健康监测），ping对方等等。尽量减少"裂脑"发生机会。(指标不治本，只是提高了检测到的概率)；
2、设置仲裁机制。两方都不可靠，那就依赖第三方。比如启用共享磁盘锁，ping网关等。(针对不同的手段还需具体分析)；
3、爆头，将master停掉。然后检查机器之间的防火墙。网络之间的通信

Nginx+keepalived实现七层的负载均衡

 

 

配置安装nginx 所有的机器，关闭防火墙和selinux
[root@proxy-master ~]# systemctl stop firewalld         //关闭防火墙
[root@proxy-master ~]# sed -i 's/^SELINUX=.*/SELINUX=disabled/' /etc/sysconfig/selinux        //关闭selinux，重启生效
[root@proxy-master ~]# setenforce 0        　　　　　　　　//关闭selinux，临时生效

安装nginx， 全部4台
[root@proxy-master ~]# cd /etc/yum.repos.d/
[root@proxy-master yum.repos.d]# vim nginx.repo
[nginx-stable]
name=nginx stable repo
baseurl=http://nginx.org/packages/centos/$releasever/$basearch/
gpgcheck=0
enabled=1
[root@proxy-master yum.repos.d]# yum install yum-utils -y
[root@proxy-master yum.repos.d]# yum install nginx -y

一、实施过程 
1、选择两台nginx服务器作为代理服务器。
2、给两台代理服务器安装keepalived制作高可用生成VIP
3、配置nginx的负载均衡
# 两台配置完全一样
[root@proxy-master ~]# vim /etc/nginx/nginx.conf
user nginx;
worker_processes auto;
error_log /var/log/nginx/error.log;
pid /run/nginx.pid;
include /usr/share/nginx/modules/*.conf;
events {
    worker_connections 1024;
}
http {
    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';
    access_log  /var/log/nginx/access.log  main;
    sendfile            on;
    tcp_nopush          on;
    tcp_nodelay         on;
    keepalive_timeout   65;
    types_hash_max_size 2048;
    include             /etc/nginx/mime.types;
    default_type        application/octet-stream;
    include /etc/nginx/conf.d/*.conf;
    upstream backend {
    server 172.16.147.154:80 weight=1 max_fails=3 fail_timeout=20s;
    server 172.16.147.153:80 weight=1 max_fails=3 fail_timeout=20s;
    }
    server {
        listen       80;
        server_name  localhost;
        location / {
        proxy_pass http://backend;
        proxy_set_header Host $host:$proxy_port;
        proxy_set_header X-Forwarded-For $remote_addr;
        }
    }
}

keepalived是实现调度HA

注：主/备调度器均能够实现正常调度
1. 主/备调度器安装软件
[root@proxy-master ~]# yum install -y keepalived
[root@proxy-slave ~]# yum install -y keepalived
[root@proxy-master ~]# cp /etc/keepalived/keepalived.conf /etc/keepalived/keepalived.conf.bak
[root@proxy-master ~]# vim /etc/keepalived/keepalived.conf
! Configuration File for keepalived

global_defs {
   router_id directory1   #辅助改为directory2
}

vrrp_instance VI_1 {
    state MASTER        #定义主还是备
    interface ens33     #VIP绑定接口
    virtual_router_id 80  #整个集群的调度器一致
    priority 100         #back改为50
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        172.16.147.100/24   # vip
    }
}

[root@proxy-slave ~]# cp /etc/keepalived/keepalived.conf /etc/keepalived/keepalived.conf.bak
[root@proxy-slave ~]# vim /etc/keepalived/keepalived.conf
! Configuration File for keepalived

global_defs {
   router_id directory2
}

vrrp_instance VI_1 {
    state BACKUP    #设置为backup
    interface ens33
    nopreempt        #设置到back上面，不抢占资源
    virtual_router_id 80
    priority 50   #辅助改为50
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        172.16.147.100/24
    }
}
3. 启动KeepAlived（主备均启动）
[root@proxy-master ~]# systemctl enable keepalived
[root@proxy-slave ~]# systemctl start keepalived
[root@proxy-master ~]# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    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
    inet 172.16.147.100/32 scope global 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 group default qlen 1000
    link/ether 00:0c:29:ec:8a:fe brd ff:ff:ff:ff:ff:ff
    inet 172.16.147.155/24 brd 172.16.147.255 scope global noprefixroute dynamic ens33
       valid_lft 1115sec preferred_lft 1115sec
    inet 172.16.147.101/24 scope global secondary ens33
       valid_lft forever preferred_lft forever

到此：
可以解决心跳故障keepalived
不能解决Nginx服务故障
4. 扩展对调度器Nginx健康检查（可选）两台都设置
思路：
让Keepalived以一定时间间隔执行一个外部脚本，脚本的功能是当Nginx失败，则关闭本机的Keepalived
(1) script
[root@proxy-master ~]# vim /etc/keepalived/check_nginx_status.sh
#!/bin/bash												        
/usr/bin/curl -I http://localhost &>/dev/null	
if [ $? -ne 0 ];then										    
#	/etc/init.d/keepalived stop
	systemctl stop keepalived
fi															        	
[root@proxy-master ~]# chmod a+x /etc/keepalived/check_nginx_status.sh

(2). keepalived使用script
! Configuration File for keepalived

global_defs {
   router_id director1
}
vrrp_script check_nginx {
   script "/etc/keepalived/check_nginx_status.sh"
   interval 5
}

vrrp_instance VI_1 {
    state MASTER
    interface ens33
    virtual_router_id 80
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        192.168.246.16/24
    }
    track_script {
        check_nginx
    }
}
注：必须先启动nginx，再启动keepalived