双主 + keepalived 是一个比较简单的 MySQL 高可用架构，适用于中小 MySQL 集群，今天就说说怎么用 keepalived 做 MySQL 的高可用。
简单地说，keepalived 就是通过管理 VIP 来实现机器的高可用的，在使用 keepalived 的情况下，只有一台服务器能够提供服务(通过 VIP 来实现)，当 Master 主机宕机后，VIP 会自动飘移到另一台服务器
keepalived 采用 Master/Slave 模式, 在 Master 上设置配置文件的 VIP，当 Master 宕机后，VIP 自动漂移到另一台 keepalived 服务器上
keepalived 可以用来做各种软件的高可用集群，它会一直检测服务器的状态，如果有一台服务器宕机，或工作出现故障，keepalived 将检测到，并将有故障的服务器从系统中剔除，同时使用其他服务器代替该服务器的工作，当服务器工作正常后 keepalived 自动将服务器加入到服务器群中。
keepalived 使用默认配置只能做到主机级别的高可用，但是我们的 MySQL 要做高可用至少要增加以下功能
read_only=0，备节点 read_only=1所以，keepalived 实现 MySQL 高可用需要使用自定义脚本来进行扩展
操作前已经准备好了一套主主架构数据库，搭建方法参考 MySQL集群搭建(2)-主主从模式
| IP | 系统 | 端口 | MySQL版本 | 节点 | 读写 | 说明 |
|---|---|---|---|---|---|---|
| 10.0.0.247 | Centos6.5 | 3306 | 5.7.9 | Master | 读写 | 主节点 |
| 10.0.0.248 | Centos6.5 | 3306 | 5.7.9 | Standby | 只读,可切换为读写 | 备主节点 |
| 简称 | VIP | 类型 |
|---|---|---|
| RW-VIP | 10.0.0.237 | 读写VIP |
[client]port = 3306default-character-set=utf8mb4socket = /data/mysql_db/test_db/mysql.sock[mysqld]datadir = /data/mysql_db/test_dbbasedir = /usr/local/mysql57tmpdir = /tmpsocket = /data/mysql_db/test_db/mysql.sockpid-file = /data/mysql_db/test_db/mysql.pidskip-external-locking = 1skip-name-resolve = 1port = 3306server_id = 2473306default-storage-engine = InnoDBcharacter-set-server = utf8mb4default_password_lifetime=0auto_increment_offset = 1auto_increment_increment = 2#### log ####log_timestamps=systemlog_bin = /data/mysql_log/test_db/mysql-binlog_bin_index = /data/mysql_log/test_db/mysql-bin.indexbinlog_format = rowrelay_log_recovery=ONrelay_log=/data/mysql_log/test_db/mysql-relay-binrelay_log_index=/data/mysql_log/test_db/mysql-relay-bin.indexlog_error = /data/mysql_log/test_db/mysql-error.log#### replication ####log_slave_updates = 1replicate_wild_ignore_table = information_schema.%,performance_schema.%,sys.%#### semi sync replication settings #####plugin_dir=/usr/local/mysql57/lib/pluginplugin_load = "rpl_semi_sync_master=semisync_master.so;rpl_semi_sync_slave=semisync_slave.so"loose_rpl_semi_sync_master_enabled = 1loose_rpl_semi_sync_slave_enabled = 1[client]port = 3306default-character-set=utf8mb4socket = /data/mysql_db/test_db/mysql.sock[mysqld]datadir = /data/mysql_db/test_dbbasedir = /usr/local/mysql57tmpdir = /tmpsocket = /data/mysql_db/test_db/mysql.sockpid-file = /data/mysql_db/test_db/mysql.pidskip-external-locking = 1skip-name-resolve = 1port = 3306server_id = 2483306default-storage-engine = InnoDBcharacter-set-server = utf8mb4default_password_lifetime=0auto_increment_offset = 2auto_increment_increment = 2#### log ####log_timestamps=systemlog_bin = /data/mysql_log/test_db/mysql-binlog_bin_index = /data/mysql_log/test_db/mysql-bin.indexbinlog_format = rowrelay_log_recovery=ONrelay_log=/data/mysql_log/test_db/mysql-relay-binrelay_log_index=/data/mysql_log/test_db/mysql-relay-bin.indexlog_error = /data/mysql_log/test_db/mysql-error.log#### replication ####log_slave_updates = 1replicate_wild_ignore_table = information_schema.%,performance_schema.%,sys.%#### semi sync replication settings #####plugin_dir=/usr/local/mysql57/lib/pluginplugin_load = "rpl_semi_sync_master=semisync_master.so;rpl_semi_sync_slave=semisync_slave.so"loose_rpl_semi_sync_master_enabled = 1loose_rpl_semi_sync_slave_enabled = 1- 由于是测试环境，账号密码设置比较随便create user monitor@‘localhost‘ identified by ‘monitor‘;grant all on *.* to monitor@‘localhost‘;flush privileges;我们在 Master 和 Slave 上部署 keepalived
如果有对应的 yum 源，直接安装就可以了
yum install -y keepalived下载安装包, 下载地址 keepalived, 使用 1.2.24 版本举例
# 安装依赖yum install -y gcc popt-devel openssl openssl-devel libssl-dev libnl-devel popt-devel libnfnetlink-devel# 下载包wget http://www.keepalived.org/software/keepalived-1.2.24.tar.gz# 解压安装tar -xvz -f keepalived-1.2.24.tar.gzcd keepalived-1.2.24./configure --prefix=/usr/local/keepalivedmake && make installcp /usr/local/keepalived/sbin/keepalived /usr/sbin/cp /usr/local/keepalived/etc/rc.d/init.d/keepalived /etc/init.d/cp /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/mkdir /etc/keepalived/cp /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/打开 /etc/keepalived/keepalived.conf 文件, 按照实际情况加上下面的配置
global_defs { router_id MYSQL_MM # 标识 vrrp_skip_check_adv_addr vrrp_strict # 严格执行 VRRP 协议规范 vrrp_garp_interval 0 vrrp_gna_interval 0}vrrp_script check_mysql { script "/bin/sh /etc/keepalived/keepalived_mysql_check.sh" # 检查脚本 interval 10 # 检查周期}vrrp_instance MYSQL_MM { state BACKUP # 都设为 BACKUP，避免起来后抢占 interface eth0 # 网卡名称，根据实际情况填写 virtual_router_id 243 # 用来区分 VRRP 组播的标记，取值 0-255 priority 100 advert_int 1 nopreempt # 设为非抢占 authentication { auth_type PASS auth_pass 1111 } # Master 节点可以注释掉下面语句，防止启动 keepalived 的时候执行脚本 notify_master "/bin/sh /etc/keepalived/keepalived_mysql_start.sh" # 变为 MASTER 时执行 virtual_ipaddress { 10.0.0.237 } # Slave 节点可以注释下面检查脚本，Slave 没有必要一直检查 track_script { check_mysql }}打开 /etc/keepalived/keepalived_mysql_check.sh， 写入检测脚本
#!/bin/sh# @Author: chengqm# MySQL 检测脚本MyPath=$(cd $(dirname $0); pwd)cd $MyPathThisTime=`date ‘+%F %T‘`log_file=‘/var/log/keepalived_mysql.log‘# MySQL 连接方式，根据实际情况调整export MYSQL_PWD=‘monitor‘MYSQL_USER=‘monitor‘MYSQL_SOCKET="/data/mysql_db/test_db/mysql.sock"mysql_connect="mysql -u${MYSQL_USER} -S${MYSQL_SOCKET} "# 美化输出function techo() { message=$1 message_level=$2 if [ -e $message_level ];then message_level=‘info‘ fi echo "`date ‘+%F %T‘` - [${message_level}] $message" >> $log_file}# 检查函数, 正常返回 0function check { ret=`$mysql_connect -N -e ‘select 1 as value‘` if [ $? -ne 0 ] || [ $ret -ne ‘1‘ ];then return 1 else return 0 fi}function read_only { param=$1 $mysql_connect -e "set global read_only = ${param}" techo "设置是否只读 read_only ${param}"}# 失效转移function failover { techo "开始执行失效转移" # 1. 停止 keepalived killall keepalived # 2. 如果还能执行的话，设为 read_only read_only 1 if [ $? -eq 0 ];then # 3. 如果还能执行，kill 所有的连接 $mysql_connect -e "select concat(‘KILL ‘,id,‘;‘) from information_schema.processlist where user!=‘root‘ AND db is not null into outfile ‘/tmp/kill.txt.${ThisTime}‘;" if [ $? -eq 0 ];then $mysql_connect -e "source /tmp/kill.txt.${ThisTime};" fi fi # 4. 其他操作，比如说自动关机 techo "失效转移执行成功，当前数据库关闭访问"}# 有问题检查 4 次for ((i=1; i<=4; i ++)) do check if [ $? -eq 0 ];then techo "MySQL is ok" # 正常退出脚本 exit 0 else techo "Connection failed $i time(s)" sleep 1 fidonetecho ‘无法连接当前数据库‘# 失效转移failover注意：脚本没有经过严格测试，需要根据实际情况调整
打开 /bin/sh /etc/keepalived/keepalived_mysql_start.sh", 写入脚本内容
#!/bin/sh# @Author: chengqm# keepalived 变为 Master 时执行MyPath=$(cd $(dirname $0); pwd)cd $MyPathThisTime=`date ‘+%F %T‘`log_file=‘/var/log/keepalived_mysql.log‘# MySQL 连接方式，根据实际情况调整export MYSQL_PWD=‘monitor‘MYSQL_USER=‘monitor‘MYSQL_SOCKET="/data/mysql_db/test_db/mysql.sock"mysql_connect="mysql -u${MYSQL_USER} -S${MYSQL_SOCKET} "# 美化输出function techo() { message=$1 message_level=$2 if [ -e $message_level ];then message_level=‘info‘ fi echo "`date ‘+%F %T‘` - [${message_level}] $message" >> $log_file}# 检查函数, 正常返回 0function check { ret=`$mysql_connect -N -e ‘select 1 as value‘` if [ $? -ne 0 ] || [ $ret -ne ‘1‘ ];then return 1 else return 0 fi}# 获取 slave status 的信息function slave_info() { tmp_file=/tmp/slave_info.tmp $mysql_connect -e ‘show slave status\G‘ > /tmp/slave_info.tmp slave_sql=`grep ‘Slave_SQL_Running:‘ $tmp_file | sed ‘s/\s*//g‘ | tr "A-Z" "a-z" | awk -F":" ‘{print $2}‘` seconds_behind_master=`grep ‘Seconds_Behind_Master:‘ $tmp_file | sed ‘s/\s*//g‘ | tr "A-Z" "a-z" | awk -F":" ‘{print $2}‘` master_log_file=`grep ‘Master_Log_File:‘ $tmp_file | head -1 | sed ‘s/\s*//g‘ | tr "A-Z" "a-z" | awk -F":" ‘{print $2}‘` master_log_pos=`grep ‘Read_Master_Log_Pos:‘ $tmp_file | sed ‘s/\s*//g‘ | tr "A-Z" "a-z" | awk -F":" ‘{print $2}‘` relay_master_log_file=`grep ‘Relay_Master_Log_File:‘ $tmp_file | sed ‘s/\s*//g‘ | tr "A-Z" "a-z" | awk -F":" ‘{print $2}‘` exec_master_log_pos=`grep ‘Exec_Master_Log_Pos:‘ $tmp_file | sed ‘s/\s*//g‘ | tr "A-Z" "a-z" | awk -F":" ‘{print $2}‘`}# 设置是否可读function read_only { param=$1 $mysql_connect -e "set global read_only = ${param}" techo "设置是否只读 read_only ${param}"}# 处理数据同步function sync_master_log() { # 如果是数据一致性优先，等待同步完毕。如果是服务可用性优先，可以注销下面的代码 slave_info if [ $slave_sql == "yes" ];then techo "当前同步位置 Master ${master_log_file} ${master_log_pos}" techo "等待同步到 Master ${master_log_file} ${master_log_pos}" $mysql_connect -e "select master_pos_wait(‘$master_log_file‘, $master_log_pos);" > /dev/null techo "同步完毕" fi}techo "当前数据库提升为主库"checkif [ $? -ne 0 ];then techo "无法连接当前数据库" exit 1fi# 等待同步sync_master_log# 设为可写read_only 0注意：脚本没有经过严格测试，需要根据实际情况调整
由于配置了 BACKUP 模式，所以两个 keepalived 先起来的是主，先后在主备节点执行
/etc/init.d/keepalived start检查 /var/log/message 日志，确认 keepalived 没有报错
检查 Master IP 状态, 确认设置了 VIP
[root@cluster01 shell]# ip addr1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo inet6 ::1/128 scope host valid_lft forever preferred_lft forever2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 link/ether fa:16:3e:de:80:33 brd ff:ff:ff:ff:ff:ff inet 10.0.0.247/16 brd 10.0.255.255 scope global eth0 inet 10.0.0.237/32 scope global eth0 inet6 fe80::f816:3eff:fede:8033/64 scope link valid_lft forever preferred_lft forever检查 MySQL 检测脚本执行情况，确认正常运行
[root@cluster01 ~]# tail -f /var/log/keepalived_mysql.log ...2019-01-28 15:04:18 - [info] MySQL is ok2019-01-28 15:04:28 - [info] MySQL is ok在 mytest 库里新建 nowdate 测试表，只有 id 和 ctime 字段，然后每秒插入一条数据
[root@cluster03 ~]# while true; do date;mysql -h10.0.0.237 -P3306 -umytest -e ‘use mytest;insert into nowdate values (null, now());‘; sleep 1;doneMon Jan 28 15:04:26 CST 2019Mon Jan 28 15:04:27 CST 2019...kill 掉 Master 进程
killall mysqld查看旧 Master 日志
2019-01-28 15:04:48 - [info] MySQL is ok2019-01-28 15:04:58 - [info] Connection failed 1 time(s)2019-01-28 15:04:59 - [info] Connection failed 2 time(s)2019-01-28 15:05:00 - [info] Connection failed 3 time(s)2019-01-28 15:05:01 - [info] Connection failed 4 time(s)2019-01-28 15:05:02 - [info] 无法连接当前数据库2019-01-28 15:05:02 - [info] 开始执行失效转移2019-01-28 15:05:02 - [info] 设置是否只读 read_only 12019-01-28 15:05:02 - [info] 失效转移执行成功，当前数据库关闭访问查看新 Master 日志
2019-01-28 15:05:04 - [info] 当前数据库提升为主库2019-01-28 15:05:04 - [info] 当前同步位置 Master mysql-bin.000015 323382019-01-28 15:05:04 - [info] 等待同步到 Master mysql-bin.000015 323382019-01-28 15:05:04 - [info] 同步完毕2019-01-28 15:05:04 - [info] 设置是否只读 read_only 02019-01-28 15:05:05 - [info] MySQL is ok查看新 Master IP，确认 VIP 已经飘过来了
[root@cluster02 ~]# ip addr1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo inet6 ::1/128 scope host valid_lft forever preferred_lft forever2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 link/ether fa:16:3e:66:7e:e8 brd ff:ff:ff:ff:ff:ff inet 10.0.0.248/16 brd 10.0.255.255 scope global eth0 inet 10.0.0.237/32 scope global eth0 inet6 fe80::f816:3eff:fe66:7ee8/64 scope link valid_lft forever preferred_lft forever查看插入数据执行情况，大概有 12 秒是不可用的
Mon Jan 28 15:04:51 CST 2019ERROR 2003 (HY000): Can‘t connect to MySQL server on ‘10.0.0.237‘ (111)Mon Jan 28 15:04:52 CST 2019ERROR 2003 (HY000): Can‘t connect to MySQL server on ‘10.0.0.237‘ (111)Mon Jan 28 15:04:53 CST 2019ERROR 2003 (HY000): Can‘t connect to MySQL server on ‘10.0.0.237‘ (111)Mon Jan 28 15:04:54 CST 2019ERROR 2003 (HY000): Can‘t connect to MySQL server on ‘10.0.0.237‘ (111)Mon Jan 28 15:04:55 CST 2019ERROR 2003 (HY000): Can‘t connect to MySQL server on ‘10.0.0.237‘ (111)Mon Jan 28 15:04:56 CST 2019ERROR 2003 (HY000): Can‘t connect to MySQL server on ‘10.0.0.237‘ (111)Mon Jan 28 15:04:57 CST 2019ERROR 2003 (HY000): Can‘t connect to MySQL server on ‘10.0.0.237‘ (111)Mon Jan 28 15:04:58 CST 2019ERROR 2003 (HY000): Can‘t connect to MySQL server on ‘10.0.0.237‘ (111)Mon Jan 28 15:05:00 CST 2019ERROR 2003 (HY000): Can‘t connect to MySQL server on ‘10.0.0.237‘ (111)Mon Jan 28 15:05:01 CST 2019ERROR 2003 (HY000): Can‘t connect to MySQL server on ‘10.0.0.237‘ (111)Mon Jan 28 15:05:02 CST 2019ERROR 2003 (HY000): Can‘t connect to MySQL server on ‘10.0.0.237‘ (111)Mon Jan 28 15:05:03 CST 2019失效切换成功
使用双主 + keepalived 的优点是部署简单，双主加半同步情况下，理论上不会丢数据，适用于中小型 MySQL 集群。缺点也比较明显，就是增加从节点的情况下，从节点不会主动切换同步对象，而且脚本需要自己实现，有一定风险。
