mysql之mha高可用及读写分离
MHA高可用
1.MHA介绍及工作原理
MHA（Master High Availability），由日本DeNA公司youshimaton（现就职于Facebook公司）开发。MHA能做到在10~30秒之内自动完成数据库的Failover，Failover的过程中，能最大程度上保证数据的一致性。
该软件由两部分组成：MHA Manager（管理节点）和MHA Node（数据节点）。
半同步复制，可以大大降低数据丢失的风险。MHA可以与半同步复制结合起来。
MHA高可用集群,要求一个复制集群中需要有三台数据库服务器，一主二从，不支持多实例。出于机器成本的考虑，淘宝也在该基础上进行了改造，淘宝TMHA支持一主一从
注意：必须使用独立的数据库节点，不支持多实例。
2.MHA企业架构图
3.MHA软件结构
Manager工具包主要包括以下几个工具：
- masterha_check_ssh 检查MHA的SSH配置状况
- masterha_check_repl 检查MySQL复制状况
- masterha_manger 启动MHA
- masterha_check_status 检测当前MHA运行状态
- masterha_master_monitor 检测master是否宕机
- masterha_conf_host 添加或删除配置的server信息
- masterha_master_switch 控制故障转移（自动或者手动）
Node工具包（这些工具通常由MHA Manager的脚本触发，无需人为操作）主要包括以下几个工具：
- save_binary_logs 保存和复制master的二进制日志
- apply_diff_relay_logs 识别差异的中继日志事件并将其差异的事件应用于其他的从节点
- slave filter_mysqlbinlog 去除不必要的ROLLBACK事件（MHA已不再使用这个工具）
- purge_relay_logs 清除中继日志（不会阻塞SQL线程）
4.MHA工作原理
1、Manager程序负责监控所有已知Node（1主2从所有节点）
2、当主库发生意外宕机
2.1 mysql实例故障（SSH能够连接到主机）
1、监控到主库宕机，选择一个新主（取消从库角色，reset slave），选择标准：数据较新的从库会被选择为新主(show slave status\G)
2、从库通过MHA自带脚本程序，立即保存缺失部分的binlog
3、二号从库会重新与新主构建主从关系，继续提供服务
4、如果VIP机制，将vip从原主库漂移到新主，让应用程序无感知
2.2 主节点服务器宕机（SSH已经连接不上了）
1、监控到主库宕机，尝试SSH连接，尝试失败
2、选择一个数据较新的从库成为新主库（取消从库角色 reset slave），判断细节：show slave status\G
3、计算从库之间的relay-log的差异，补偿到2号从库
4、二号从库会重新与新主构建主从关系，继续提供服务
5、如果VIP机制，将vip从原主库漂移到新主，让应用程序无感知
6、如果有binlog server机制，会继续讲binlog server中的记录的缺失部分的事务，补偿到新的主库
5.MHA搭建过程(需要在GTID的环境上进行搭建)
5.1 在/etc/my.cnf配置文件中添加(每个节点都要添加)
relay_log_purge=0 #保留mysql中relay_log
每个节点都需要做好解析
172.16.1.51 db01
172.16.1.52 db02
172.16.1.53 db03
5.2 各个节点安装mha node
mha下载地址：https://github.com/yoshinorim/mha4mysql-manager/releases
每个点都需要进行安装mha-node
yum -y install mha4mysql-node-0.58-0.el7.centos.noarch.rpm
5.3 在主库上新建mha管理用户
grant all privileges on *.* to mha@'172.16.1.%' identified by 'mha';
5.4 配置软件链接
ln -s /application/mysql/bin/mysqlbinlog /usr/bin/mysqlbinlog
ln -s /application/mysql/bin/mysql /usr/bin/mysql
5.5 部署manage节点(生产环境一般拿多一台服务器做manage节点，此处使用db03)
yum -y install mha4mysql-manager-0.58-0.el7.centos.noarch.rpm
5.6 创建manage目录与配置文件
mkdir -p /etc/mha
mkdir -p /var/log/mha/app1 ----》可以管理多套主从复制
vim /etc/mha/app1.cnf
[server default]
manager_log=/var/log/mha/app1/manager
manager_workdir=/var/log/mha/app1
master_binlog_dir=/data/binlog
user=mha
password=mha
ping_interval=2
repl_password=123
repl_user=repl
ssh_user=root
[server1]
hostname=172.16.1.51
port=3306
[server2]
hostname=172.16.1.52
port=3306
[server3]
hostname=172.16.1.53
port=3306
5.7配置各节点ssh互信
ssh-keygen -t dsa -P '' -f ~/.ssh/id_dsa >/dev/null 2>&1
ssh-copy-id -i /root/.ssh/id_dsa.pub root@172.16.1.51
ssh-copy-id -i /root/.ssh/id_dsa.pub root@172.16.1.52
ssh-copy-id -i /root/.ssh/id_dsa.pub root@172.16.1.53
5.8 检查互信
[root@db03 tools]# masterha_check_ssh --conf=/etc/mha/app1.cnf
Tue Apr 30 20:04:52 2019 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping
.Tue Apr 30 20:04:52 2019 - [info] Reading application default configuration from /etc/mha/app1.cnf..
Tue Apr 30 20:04:52 2019 - [info] Reading server configuration from /etc/mha/app1.cnf..
Tue Apr 30 20:04:52 2019 - [info] Starting SSH connection tests..
Tue Apr 30 20:04:53 2019 - [debug]
Tue Apr 30 20:04:52 2019 - [debug] Connecting via SSH from root@172.16.1.51(172.16.1.51:22) to root@172.16.
1.52(172.16.1.52:22)..Tue Apr 30 20:04:52 2019 - [debug] ok.
Tue Apr 30 20:04:52 2019 - [debug] Connecting via SSH from root@172.16.1.51(172.16.1.51:22) to root@172.16.
1.53(172.16.1.53:22)..Tue Apr 30 20:04:53 2019 - [debug] ok.
Tue Apr 30 20:04:53 2019 - [debug]
Tue Apr 30 20:04:52 2019 - [debug] Connecting via SSH from root@172.16.1.52(172.16.1.52:22) to root@172.16.
1.51(172.16.1.51:22)..Tue Apr 30 20:04:53 2019 - [debug] ok.
Tue Apr 30 20:04:53 2019 - [debug] Connecting via SSH from root@172.16.1.52(172.16.1.52:22) to root@172.16.
1.53(172.16.1.53:22)..Tue Apr 30 20:04:53 2019 - [debug] ok.
Tue Apr 30 20:04:53 2019 - [error][/usr/share/perl5/vendor_perl/MHA/SSHCheck.pm, ln63]
Tue Apr 30 20:04:53 2019 - [debug] Connecting via SSH from root@172.16.1.53(172.16.1.53:22) to root@172.16.
1.51(172.16.1.51:22)..Warning: Permanently added '172.16.1.53' (ECDSA) to the list of known hosts.
Permission denied (publickey,password).
Tue Apr 30 20:04:53 2019 - [error][/usr/share/perl5/vendor_perl/MHA/SSHCheck.pm, ln111] SSH connection from
root@172.16.1.53(172.16.1.53:22) to root@172.16.1.51(172.16.1.51:22) failed!SSH Configuration Check Failed!
at /usr/bin/masterha_check_ssh line 44.
[root@db03 tools]#
5.9 检查主从
[root@db03 tools]# masterha_check_ssh --conf=/etc/mha/app1.cnf
Tue Apr 30 20:04:52 2019 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping
.Tue Apr 30 20:04:52 2019 - [info] Reading application default configuration from /etc/mha/app1.cnf..
Tue Apr 30 20:04:52 2019 - [info] Reading server configuration from /etc/mha/app1.cnf..
Tue Apr 30 20:04:52 2019 - [info] Starting SSH connection tests..
Tue Apr 30 20:04:53 2019 - [debug]
Tue Apr 30 20:04:52 2019 - [debug] Connecting via SSH from root@172.16.1.51(172.16.1.51:22) to root@172.16.
1.52(172.16.1.52:22)..Tue Apr 30 20:04:52 2019 - [debug] ok.
Tue Apr 30 20:04:52 2019 - [debug] Connecting via SSH from root@172.16.1.51(172.16.1.51:22) to root@172.16.
1.53(172.16.1.53:22)..Tue Apr 30 20:04:53 2019 - [debug] ok.
Tue Apr 30 20:04:53 2019 - [debug]
Tue Apr 30 20:04:52 2019 - [debug] Connecting via SSH from root@172.16.1.52(172.16.1.52:22) to root@172.16.
1.51(172.16.1.51:22)..Tue Apr 30 20:04:53 2019 - [debug] ok.
Tue Apr 30 20:04:53 2019 - [debug] Connecting via SSH from root@172.16.1.52(172.16.1.52:22) to root@172.16.
1.53(172.16.1.53:22)..Tue Apr 30 20:04:53 2019 - [debug] ok.
Tue Apr 30 20:04:53 2019 - [error][/usr/share/perl5/vendor_perl/MHA/SSHCheck.pm, ln63]
Tue Apr 30 20:04:53 2019 - [debug] Connecting via SSH from root@172.16.1.53(172.16.1.53:22) to root@172.16.
1.51(172.16.1.51:22)..Warning: Permanently added '172.16.1.53' (ECDSA) to the list of known hosts.
Permission denied (publickey,password).
Tue Apr 30 20:04:53 2019 - [error][/usr/share/perl5/vendor_perl/MHA/SSHCheck.pm, ln111] SSH connection from
root@172.16.1.53(172.16.1.53:22) to root@172.16.1.51(172.16.1.51:22) failed!SSH Configuration Check Failed!
at /usr/bin/masterha_check_ssh line 44.
[root@db03 tools]# masterha_check_repl --conf=/etc/mha/app1.cnf
Tue Apr 30 20:05:38 2019 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping
.Tue Apr 30 20:05:38 2019 - [info] Reading application default configuration from /etc/mha/app1.cnf..
Tue Apr 30 20:05:38 2019 - [info] Reading server configuration from /etc/mha/app1.cnf..
Tue Apr 30 20:05:38 2019 - [info] MHA::MasterMonitor version 0.58.
Tue Apr 30 20:05:40 2019 - [info] GTID failover mode = 1
Tue Apr 30 20:05:40 2019 - [info] Dead Servers:
Tue Apr 30 20:05:40 2019 - [info] Alive Servers:
Tue Apr 30 20:05:40 2019 - [info] 172.16.1.51(172.16.1.51:3306)
Tue Apr 30 20:05:40 2019 - [info] 172.16.1.52(172.16.1.52:3306)
Tue Apr 30 20:05:40 2019 - [info] 172.16.1.53(172.16.1.53:3306)
Tue Apr 30 20:05:40 2019 - [info] Alive Slaves:
Tue Apr 30 20:05:40 2019 - [info] 172.16.1.52(172.16.1.52:3306) Version=5.6.43-log (oldest major version
between slaves) log-bin:enabledTue Apr 30 20:05:40 2019 - [info] GTID ON
Tue Apr 30 20:05:40 2019 - [info] Replicating from 172.16.1.51(172.16.1.51:3306)
Tue Apr 30 20:05:40 2019 - [info] 172.16.1.53(172.16.1.53:3306) Version=5.6.43-log (oldest major version
between slaves) log-bin:enabledTue Apr 30 20:05:40 2019 - [info] GTID ON
Tue Apr 30 20:05:40 2019 - [info] Replicating from 172.16.1.51(172.16.1.51:3306)
Tue Apr 30 20:05:40 2019 - [info] Current Alive Master: 172.16.1.51(172.16.1.51:3306)
Tue Apr 30 20:05:40 2019 - [info] Checking slave configurations..
Tue Apr 30 20:05:40 2019 - [info] read_only=1 is not set on slave 172.16.1.52(172.16.1.52:3306).
Tue Apr 30 20:05:40 2019 - [info] read_only=1 is not set on slave 172.16.1.53(172.16.1.53:3306).
Tue Apr 30 20:05:40 2019 - [info] Checking replication filtering settings..
Tue Apr 30 20:05:40 2019 - [info] binlog_do_db= , binlog_ignore_db=
Tue Apr 30 20:05:40 2019 - [info] Replication filtering check ok.
Tue Apr 30 20:05:40 2019 - [info] GTID (with auto-pos) is supported. Skipping all SSH and Node package check
ing.Tue Apr 30 20:05:40 2019 - [info] Checking SSH publickey authentication settings on the current master..
Tue Apr 30 20:05:40 2019 - [info] HealthCheck: SSH to 172.16.1.51 is reachable.
Tue Apr 30 20:05:40 2019 - [info]
172.16.1.51(172.16.1.51:3306) (current master)
+--172.16.1.52(172.16.1.52:3306)
+--172.16.1.53(172.16.1.53:3306)
Tue Apr 30 20:05:40 2019 - [info] Checking replication health on 172.16.1.52..
Tue Apr 30 20:05:40 2019 - [info] ok.
Tue Apr 30 20:05:40 2019 - [info] Checking replication health on 172.16.1.53..
Tue Apr 30 20:05:40 2019 - [info] ok.
Tue Apr 30 20:05:40 2019 - [warning] master_ip_failover_script is not defined.
Tue Apr 30 20:05:40 2019 - [warning] shutdown_script is not defined.
Tue Apr 30 20:05:40 2019 - [info] Got exit code 0 (Not master dead).
MySQL Replication Health is OK.
[root@db03 tools]#
5.10 启动mha
nohup masterha_manager --conf=/etc/mha/app1.cnf --remove_dead_master_conf --ignore_last_failover < /dev/null > /var/log/mha/app1/manager.log 2>&1 &
6.故障演练
6.1 宕掉主库(db01)
[root@db01 tools]# /etc/init.d/mysqld stop
Shutting down MySQL...... SUCCESS!
6.2 查看mha日志
[root@db03 ~]# cat /var/log/mha/app1/manager
......
CHANGE MASTER TO MASTER_HOST='172.16.1.52', MASTER_PORT=3306, MASTER_AUTO_POSITION=1, MASTER_USER='repl', MASTER_PASSWORD='xxx'; #此处是恢复故障机的命令
......
----- Failover Report -----
app1: MySQL Master failover 172.16.1.51(172.16.1.51:3306) to 172.16.1.52(172.16.1.52:3306) succeeded
Master 172.16.1.51(172.16.1.51:3306) is down!
Check MHA Manager logs at db03:/var/log/mha/app1/manager for details.
Started automated(non-interactive) failover.
Selected 172.16.1.52(172.16.1.52:3306) as a new master.
172.16.1.52(172.16.1.52:3306): OK: Applying all logs succeeded.
172.16.1.53(172.16.1.53:3306): OK: Slave started, replicating from 172.16.1.52(172.16.1.52:3306)
172.16.1.52(172.16.1.52:3306): Resetting slave info succeeded.
Master failover to 172.16.1.52(172.16.1.52:3306) completed successfully. #此处表示已经成功切换到52这一台机器了
6.3 查看db03
mysql> show slave status\G
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 172.16.1.52 #已成功切换到db02
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000001
Read_Master_Log_Pos: 805
Relay_Log_File: db03-relay-bin.000002
Relay_Log_Pos: 408
Relay_Master_Log_File: mysql-bin.000001
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_Do_DB:
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno: 0
Last_Error:
Skip_Counter: 0
Exec_Master_Log_Pos: 805
Relay_Log_Space: 611
Until_Condition: None
Until_Log_File:
Until_Log_Pos: 0
Master_SSL_Allowed: No
Master_SSL_CA_File:
Master_SSL_CA_Path:
Master_SSL_Cert:
Master_SSL_Cipher:
Master_SSL_Key:
Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 0
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id: 52
Master_UUID: 901b2d37-6af9-11e9-9c6c-000c29481d4a
Master_Info_File: /application/mysql/data/master.info
SQL_Delay: 0
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it
Master_Retry_Count: 86400
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set:
Executed_Gtid_Set: fac6353b-6a35-11e9-9770-000c29c0e349:1-3
Auto_Position: 1
1 row in set (0.00 sec)
6.3 恢复db01
1.在db01上，将db01重新加入到主从复制
[root@db01 tools]# /etc/init.d/mysqld start
CHANGE MASTER TO MASTER_HOST='172.16.1.52', MASTER_PORT=3306, MASTER_AUTO_POSITION=1, MASTER_USER='repl',MASTER_PASSWORD='123';
start slave
2.在mha配置文件中重新加入db01
[root@db03 tools]# vim /etc/mha/app1.cnf
[server default]
......
[server1]
hostname=172.16.1.51
port=3306
......
3.启动MHA了manager程序
masterha_check_ssh --conf=/etc/mha/app1.cnf
masterha_check_ssh --conf=/etc/mha/app1.cnf
nohup masterha_manager --conf=/etc/mha/app1.cnf --remove_dead_master_conf --ignore_last_failover < /dev/null > /var/log/mha/app1/manager.log 2>&1 &
7.使用MHA自带脚本实现IP FailOver(vip 漂移，应用透明)
7.1 上传脚本
[root@db03 bin]# cat master_ip_failover
#!/usr/bin/env perl
use strict;
use warnings FATAL => 'all';
use Getopt::Long;
my (
$command, $ssh_user, $orig_master_host, $orig_master_ip,
$orig_master_port, $new_master_host, $new_master_ip, $new_master_port
);
my $vip = '10.0.0.55/24';
my $key = '1';
my $ssh_start_vip = "/sbin/ifconfig eth1:$key $vip";
my $ssh_stop_vip = "/sbin/ifconfig eth1:$key down";
GetOptions(
'command=s' => \$command,
'ssh_user=s' => \$ssh_user,
'orig_master_host=s' => \$orig_master_host,
'orig_master_ip=s' => \$orig_master_ip,
'orig_master_port=i' => \$orig_master_port,
'new_master_host=s' => \$new_master_host,
'new_master_ip=s' => \$new_master_ip,
'new_master_port=i' => \$new_master_port,
);
exit &main();
sub main {
print "\n\nIN SCRIPT TEST====$ssh_stop_vip==$ssh_start_vip===\n\n";
if ( $command eq "stop" || $command eq "stopssh" ) {
my $exit_code = 1;
eval {
print "Disabling the VIP on old master: $orig_master_host \n";
&stop_vip();
$exit_code = 0;
};
if ($@) {
warn "Got Error: $@\n";
exit $exit_code;
}
exit $exit_code;
}
elsif ( $command eq "start" ) {
my $exit_code = 10;
eval {
print "Enabling the VIP - $vip on the new master - $new_master_host \n";
&start_vip();
$exit_code = 0;
};
if ($@) {
warn $@;
exit $exit_code;
}
exit $exit_code;
}
elsif ( $command eq "status" ) {
print "Checking the Status of the script.. OK \n";
exit 0;
}
else {
&usage();
exit 1;
}
}
sub start_vip() {
`ssh $ssh_user\@$new_master_host \" $ssh_start_vip \"`;
}
sub stop_vip() {
return 0 unless ($ssh_user);
`ssh $ssh_user\@$orig_master_host \" $ssh_stop_vip \"`;
}
sub usage {
print
"Usage: master_ip_failover --command=start|stop|stopssh|status --orig_master_host=host --orig_master_ip=
ip --orig_master_port=port --new_master_host=host --new_master_ip=ip --new_master_port=port\n";
[root@db03 bin]# dos2unix /usr/local/bin/master_ip_failover
[root@db03 bin]# chmod +x master_ip_failover
7.2 在mha配置文件中添加
[root@db03 bin]# vim /etc/mha/app1.cnf
[server default]
......
master_ip_failover_script=/usr/local/bin/master_ip_failover
......
7.3 修改master_ip_failover配置文件
my $vip = '172.16.1.100/24';
my $key = '1';
my $ssh_start_vip = "/sbin/ifconfig eth1:$key $vip";
my $ssh_stop_vip = "/sbin/ifconfig eth1:$key down";
7.4 重启mha
masterha_stop --conf=/etc/mha/app1.cnf
nohup masterha_manager --conf=/etc/mha/app1.cnf --remove_dead_master_conf --ignore_last_failover < /dev/null > /var/log/mha/app1/manager.log 2>&1 &
7.5 手工在主库上绑定vip，注意一定要和配置文件中的ethN一致，我的是eth1:1(1是key指定的值)
ifconfig eth1:1 172.16.1.100/24 #如最小化安装没有ifconfig 命令则需要使用yum -y install net-tools安装
[root@db02 tools]# ip a
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 00:0c:29:48:1d:54 brd ff:ff:ff:ff:ff:ff
inet 172.16.1.52/24 brd 172.16.1.255 scope global eth1
valid_lft forever preferred_lft forever
inet 172.16.1.100/24 brd 172.16.1.255 scope global secondary eth1:1
valid_lft forever preferred_lft forever
7.6 切换测试
停止主库
[root@db02 tools]# /etc/init.d/mysqld stop
Shutting down MySQL...... SUCCESS!
此时发现vip已经在db01上了
[root@db01 tools]# ip a
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 00:0c:29:c0:e3:53 brd ff:ff:ff:ff:ff:ff
inet 172.16.1.51/24 brd 172.16.1.255 scope global eth1
valid_lft forever preferred_lft forever
inet 172.16.1.100/24 brd 172.16.1.255 scope global secondary eth1:1
valid_lft forever preferred_lft forever
7.7 恢复db02主从复制关系
mysql> CHANGE MASTER TO MASTER_HOST='172.16.1.51', MASTER_PORT=3306, MASTER_AUTO_POSITION=1, MASTER_USER='re
pl',MASTER_PASSWORD='123';
在mha配置文件中加入
[server2]
hostname=172.16.1.52
port=3306
启动mha
8.实现外部数据补偿(binlogserver配置)
生产环境中一般是找一台额外的机器，必须要有5.6以上的版本，支持gtid并开启，我们直接用的是db03
8.1 在mha配置文件中加入
[root@db03 bin]# vim /etc/mha/app1.cnf
[server default]
manager_log=/var/log/mha/app1/manager
manager_workdir=/var/log/mha/app1
master_binlog_dir=/data/binlog
master_ip_failover_script=/usr/local/bin/master_ip_failover
password=mha
ping_interval=2
repl_password=123
repl_user=repl
ssh_user=root
user=mha
[server1]
hostname=172.16.1.51
port=3306
[server2]
hostname=172.16.1.52
port=3306
[binlog1]
no_master=1
hostname=172.16.1.53
master_binlog_dir=/data/mysql/binlog #提前创建好,这个目录不能和原有的binlog一致
mkdir -p /data/mysql/binlog
chown -R mysql.mysql /data/mysql/*
8.2 拉取主库binlog文件
cd /data/mysql/binlog -----》必须进入到自己创建好的目录
mysqlbinlog -R --host=172.16.1.51 --user=mha --password=mha --raw --stop-never mysql-bin.000001 &
8.3 重启mha
masterha_stop --conf=/etc/mha/app1.cnf
nohup masterha_manager --conf=/etc/mha/app1.cnf --remove_dead_master_conf --ignore_last_failover < /dev/null > /var/log/mha/app1/manager.log 2>&1 &
8.4 测试
刷新binlog日志在主库上
mysql> flush logs;
查看binserver目录
[root@db03 binlog]# ls
mysql-bin.000001 mysql-bin.000002 mysql-bin.000003 mysql-bin.000004
9.其它参数说明
ping_interval=2(在server标签下设置) manager检测节点存活的间隔时间，总共会探测4次。
candidate_master=1(在节点标签下设置)
#设置为候选master，如果设置该参数以后，发生主从切换以后将会将此从库提升为主库，即使这个主库不是集群中事件最新的slave，默认情况下如果一个slave落后master 100M的relay logs的话，MHA将不会选择该slave作为一个新的master，因为对于这个slave的恢复需要花费很长时间，通过设置check_repl_delay=0,MHA触发切换在选择一个新的master的时候将会忽略复制延时，这个参数对于设置了candidate_master=1的主机非常有用，因为这个候选主在切换的过程中一定是新的master
check_repl_delay=0（节点标签下设置） #用防止master故障时,切换时slave有延迟,卡在那里切不过来
10.Mysql之Atlas(读写分离)
Atlas 是由 Qihoo 360公司Web平台部基础架构团队开发维护的一个基于MySQL协议的数据中间层项目。它在MySQL官方推出的MySQL-Proxy 0.8.2版本的基础上，修改了大量bug，添加了很多功能特性。目前该项目在360公司内部得到了广泛应用，很多MySQL业务已经接入了Atlas平台，每天承载的读写请求数达几十亿条。
源码Github： https://github.com/Qihoo360/Atlas
10.1 Atlas的功用与应用场景
Atlas的功能有：读写分离、从库负载均衡、自动分表、IP过滤、SQL语句黑白名单、DBA可平滑上下线DB、自动摘除宕机的DB
Atlas的使用场景：Atlas是一个位于前端应用与后端MySQL数据库之间的中间件，它使得应用程序员无需再关心读写分离、分表等与MySQL相关的细节，可以专注于编写业务逻辑，同时使得DBA的运维工作对前端应用透明，上下线DB前端应用无感知
10.2 Atlas的安装过程
下载地址：https://github.com/Qihoo360/Atlas/releases
注意：
1、Atlas只能安装运行在64位的系统上
2、Centos 5.X安装 Atlas-XX.el5.x86_64.rpm，Centos 6.X安装Atlas-XX.el6.x86_64.rpm(经过测试centos7也可以使用6的版本)
3、后端mysql版本应大于5.1，建议使用Mysql 5.6以上
1.安装altas
rpm -ivh Atlas-2.2.1.el6.x86_64.rpm
2.修改配置文件
cd /usr/local/mysql-proxy/
cp test.cnf test.cnf.bak
vim /usr/local/mysql-proxy/conf/test.cnf
[mysql-proxy]
admin-username = user
admin-password = pwd
proxy-backend-addresses = 172.16.1.100:3306 # 设置写入主库vip的地址
proxy-read-only-backend-addresses = 172.16.1.52:3306,10.0.0.53:3306 # 设置只读的从库地址
pwds = repl:3yb5jEku5h4=,mha:O2jBXONX098= # 设置数据库管理用户，加密方法：/usr/local/mysql-proxy/bin/encrypt 密码
daemon = true
keepalive = true
event-threads = 8
log-level = message
log-path = /usr/local/mysql-proxy/log
sql-log=ON
proxy-address = 0.0.0.0:33060
admin-address = 0.0.0.0:2345
charset=utf8
3.启动atlas
/usr/local/mysql-proxy/bin/mysql-proxyd test start
10.3 Atlas读写分离测试
读测试
mysql -umha -pmha -h172.16.1.53 -P33060
show variables like 'server_id';
mysql> show variables like 'server_id';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| server_id | 52 |
+---------------+-------+
1 row in set (0.01 sec)
mysql> show variables like 'server_id';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| server_id | 53 |
+---------------+-------+
1 row in set (0.00 sec)
写测试
set global read_only=1; # 设置两个从节点为只读模式
mysql -umha -pmha -h172.16.1.53 -P33060
create database db1;
10.4 Atlas管理之添删节点
连接管理接口：
mysql -uuser -ppwd -h127.0.0.1 -P2345
打印帮助：
mysql> select * from help;
+----------------------------+---------------------------------------------------------+
| command | description |
+----------------------------+---------------------------------------------------------+
| SELECT * FROM help | shows this help |
| SELECT * FROM backends | lists the backends and their state |
| SET OFFLINE $backend_id | offline backend server, $backend_id is backend_ndx's id |
| SET ONLINE $backend_id | online backend server, ... |
| ADD MASTER $backend | example: "add master 127.0.0.1:3306", ... |
| ADD SLAVE $backend | example: "add slave 127.0.0.1:3306", ... |
| REMOVE BACKEND $backend_id | example: "remove backend 1", ... |
| SELECT * FROM clients | lists the clients |
| ADD CLIENT $client | example: "add client 192.168.1.2", ... |
| REMOVE CLIENT $client | example: "remove client 192.168.1.2", ... |
| SELECT * FROM pwds | lists the pwds |
| ADD PWD $pwd | example: "add pwd user:raw_password", ... |
| ADD ENPWD $pwd | example: "add enpwd user:encrypted_password", ... |
| REMOVE PWD $pwd | example: "remove pwd user", ... |
| SAVE CONFIG | save the backends to config file |
| SELECT VERSION | display the version of Atlas |
+----------------------------+---------------------------------------------------------+
16 rows in set (0.00 sec)
查看所有节点
mysql> SELECT * FROM backends;
+-------------+-------------------+-------+------+
| backend_ndx | address | state | type |
+-------------+-------------------+-------+------+
| 1 | 172.16.1.100:3306 | up | rw |
| 2 | 172.16.1.52:3306 | up | ro |
| 3 | 172.16.1.53:3306 | up | ro |
+-------------+-------------------+-------+------+
3 rows in set (0.00 sec)
动态删除节点：
mysql> REMOVE BACKEND 3;
Empty set (0.00 sec)
mysql> SELECT * FROM backends;
+-------------+-------------------+-------+------+
| backend_ndx | address | state | type |
+-------------+-------------------+-------+------+
| 1 | 172.16.1.100:3306 | up | rw |
| 2 | 172.16.1.52:3306 | up | ro |
+-------------+-------------------+-------+------+
2 rows in set (0.00 sec)
动态添加节点：
mysql> ADD SLAVE 172.16.1.53:3306;
Empty set (0.00 sec)
mysql> SELECT * FROM backends;
+-------------+-------------------+-------+------+
| backend_ndx | address | state | type |
+-------------+-------------------+-------+------+
| 1 | 172.16.1.100:3306 | up | rw |
| 2 | 172.16.1.52:3306 | up | ro |
| 3 | 172.16.1.53:3306 | up | ro |
+-------------+-------------------+-------+------+
3 rows in set (0.00 sec)
将修改保存至配置文件中
SAVE CONFIG;
10.5 Atlas之自动分表功能
使用Atlas的分表功能时，首先需要在配置文件test.cnf设置tables参数。
tables参数设置格式：数据库名.表名.分表字段.子表数量，
比如：
你的数据库名叫school，表名叫stu，分表字段叫id，总共分为2张表，那么就写school.stu.id.2，如果还有其他的分表，以逗号分隔即可。
用户需要手动建立2张子表（stu_0,stu_1，注意子表序号是从0开始的）。所有的子表必须在DB的同一个database里。
当通过Atlas执行（SELECT、DELETE、UPDATE、INSERT、REPLACE）操作时，Atlas会根据分表结果（id%2=k），定位到相应的子表（stu_k）。例如，执行select * from stu where id=3;，Atlas会自动从stu_1这张子表返回查询结果。但如果执行SQL语句（select * from stu;）时不带上id，则会提示执行stu 表不存在。
Atlas暂不支持自动建表和跨库分表的功能。
Atlas目前支持分表的语句有SELECT、DELETE、UPDATE、INSERT、REPLACE。
10.5.1 Atlas自动分表配置
配置文件
vim /usr/local/mysql-proxy/conf/test.cnf
tables = school.stu.id.5
重启atlas
(主库)手工创建,分表后的库和表,分别为定义的school 和 stu_0 stu_1 stu_2 stu_3 stu_4
create database school;
use school
create table stu_0 (id int,name varchar(20));
create table stu_1 (id int,name varchar(20));
create table stu_2 (id int,name varchar(20));
create table stu_3 (id int,name varchar(20));
create table stu_4 (id int,name varchar(20));
测试:
insert into stu values (3,'wang5');
insert into stu values (2,'li4');
insert into stu values (1,'zhang3');
insert into stu values (4,'m6');
insert into stu values (5,'zou7');
commit;
10.6 IP过滤与SQL黑名单
IP过滤：client-ips 该参数用来实现IP过滤功能。
在传统的开发模式中，应用程序直接连接DB，因此DB会对部署应用的机器(比如web服务器)的IP作访问授权。
在引入中间层后，因为连接DB的是Atlas，所以DB改为对部署Atlas的机器的IP作访问授权，如果任意一台客户端都可以连接Atlas，就会带来潜在的风险。
client-ips参数用来控制连接Atlas的客户端的IP，可以是精确IP，也可以是IP段，以逗号分隔写在一行上即可。
如：
client-ips=192.168.1.2, 192.168.2，这就代表192.168.1.2这个IP和192.168.2.*这个段的IP可以连接Atlas，其他IP均不能连接。
如果该参数不设置，则任意IP均可连接Atlas。
如果设置了client-ips参数，且Atlas前面挂有LVS，则必须设置lvs-ips参数，否则可以不设置lvs-ips。
SQL语句黑白名单
Atlas会屏蔽不带where条件的delete和update操作，以及sleep函数。
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