MHA工作原理总结如下：
![wKioL1ilGaODlmlEAAKL8bGf1TM928.png-wh_50]( "11.png")
1、 配置文件检查阶段（整个集群的配置）
2、 宕机奔溃的master保存二进制日志事件且摘除VIP操作
3、 识别含有最新更新的slave
4、 复制dead master和slave相差的中继日志，保存到mha manager具体的目录下面
5、 提升一个slave为新的master
6、 使其他的slave连接新的master进行复制
复制机制：
异步复制：
MySQL默认是异步复制，MASTER将事件写入BINLOG，但并不知道SLAVE是否何时已经接收且处理，在异步复制的机制的情况下，如果MASTER宕机，事务在MASTER上已提交，但很可能这些事务没有传到任何的SLAVE上，此时SLAVE可能会丢失事务
同步复制：
MASTER提交事务，直到事务在所有的SLAVE都已提交，此时才会返回客户端，事务执行完毕，完成一个事务可能会有很大的延迟。
半同步复制：
当SLAVE主机连接到MASTER时，能够查看其是否处于半同步复制的机制。当MASTER上开启半同步复制的功能时，至少应该有一个SLAVE开启其功能，此时，一个线程在MASTER上提交事务将受到阻塞，直到得知一个已开启半同步复制功能的SLAVE已收到此事务的所有事件，或等待超时，当一个事务都写入其relay-log中且已刷新到磁盘上，SLAVE才会告知已收到，如果等待超时，也就是MASTER没呗告知已收到，此时MASTER会自动转换为异步复制，当至少一个半同步的SLAVE赶上，MASTER与其SLAVE自动转换为半同步复制的机制
半同步复制工作机制处于同步和异步之间，MASTER的事务提交阻塞，只要一个SLAVE已收到该事务的事件且已记录，他不会等待所有的SLAVE都告知已收到，且他只是接收，并不用等其他执行且提交。
MHA的隐患：
在MHA自动故障切换的过程中，MHA试图从宕掉的主服务器上保存二进制日志，最大程度保证数据的不丢失，存在的问题是，如果主服务器硬件故障宕机或无法通过SSH访问，MHA没有办法保存二进制日志，只能进行故障转移而可能丢失最新数据。，
MySQL服务挂了，可以从服务器拷贝二进制日志，若是硬件话，只能GG了，如果复制出现延迟，也只能GG了。
使用场景：
MHA主要支持一主多从的架构，要求一个复制集群必须至少有3台数据库服务器。
简介：Master HighAvailability
该软件由两部分组成：MHA Manager（管理节点）和MHA Node（数据节点）
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_master_switch 控制故障转移（自动或者手动）
masterha_conf_host 添加或删除配置的server信息
Node工具包
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）
##关闭relay log自动清楚，set globalrelay_log_purge=0
MHA在发生切换的过程中，从库的恢复过程中依赖于RELAY LOG的相关信息，所以这里要将RELAYLOG的自动清楚设置为OFF，采用手动清楚的方式。
PURGE_RELAY_LOGS工具原理：它可以为中继日志创建硬链接，执行SET GOLBAL RELAY_LOG_PURGE=1,等待几秒钟以便SQL线程切换到新的中继日志，在执行RELAY_LOG_PURGE=0
Mha 安装
1、在所有节点安装MHA node所需的perl模块（DBD:mysql）
yum install perl-DBD-MySQL -y
2、在所有节点安装mha node
tar -xvf mha4mysql-node-0.53.tar.gz
cd mha4mysql-node-0.53
perl Makefile.PL
make
make install
安装后再/usr/local/bin下生成以下文件
ll /usr/local/bin/apply_diff_relay_logs/usr/local/bin/filter_mysqlbinlog /usr/local/bin/purge_relay_logs/usr/local/bin/save_binary_logs
3、安装MHA Manager
安装相关软件
yum -y install perl-DBD-MySQLperl-Config-Tiny perl-Log-Dispatch perl-Parallel-ForkManagerperl-Config-IniFiles ncftp perl-Params-Validate perl-CPAN perl-Test-Mock-LWP.noarchperl-LWP-Authen-Negotiate.noarch perl-devel perl-ExtUtils-CBuilderperl-ExtUtils-MakeMaker
cd mha4mysql-manager-0.53
perl Makefile.PL
make
make install
拷贝相关脚本到/usr/local/bin下
cd/usr/local/mha4mysql-manager-0.53/samples/scripts
scp * /usr/local/bin
master_ip_failover #自动切换时vip管理的脚本，不是必须，如果我们使用keepalived的，我们可以自己编写脚本完成对vip的管理，比如监控mysql，如果mysql异常，我们停止keepalived就行，这样vip就会自动漂移
master_ip_online_change #在线切换时vip的管理，不是必须，同样可以可以自行编写简单的shell完成
power_manager #故障发生后关闭主机的脚本，不是必须
send_report #因故障切换后发送报警的脚本，不是必须，可自行编写简单的shell完成。
4、配置SSH登录无密码验证
1）在每台发服务器上执行：ssh-keygen-t rsa
ssh-copy-id -i.ssh/id_rsa.pub "root@192.168.28.87"
ssh-copy-id -i.ssh/id_rsa.pub "root@192.168.28.70"
ssh-copy-id -i .ssh/id_rsa.pub "root@192.168.28.71”
5、两台Slave服务设置read_only
set global read_only=1;
6、relay_log脚本
#!/bin/bash
user=root
passwd=123456
port=3306
log_dir='/data/masterha/log'
work_dir='/data'
purge='/usr/local/bin/purge_relay_logs'
if [ ! -d $log_dir ]then
mkdir $log_dir -p
Fi
$purge --user=$user --password=$passwd --disable_relay_log_purge --port=$port --workdir=$work_dir >> $log_dir/purge_relay_logs.log 2>&1
设置定时任务
0 4 * * * /bin/bash /root/purge_relay_log.sh
7、在master库创建监控用户
grant all privileges on *.* to 'root'@'192.168.1.%'identified by '125746';
flush privileges;
8、配置mha
1）创建MHA的工作目录，并且创建相关配置文件
mkdir -p /etc/masterha
cd/usr/local/mha4mysql-manager-0.53/samples/conf
cp app1.cnf /etc/masterha/
2）修改配置文件
vi/etc/masterha/app1.cnf
[server default]
manager_workdir=/var/log/masterha
manager_log=/var/log/masterha/app1/manager.log
master_binlog_dir=/data/mysql
master_ip_failover_script=/usr/local/bin/master_ip_failover
master_ip_online_change_script=/usr/local/bin/master_ip_online_change
password=125746
user=root
ping_interval=1
remote_workdir=/tmp
repl_password=123
repl_user=repl
report_script=/usr/local/bin/send_report
ssh_user=root
[server1]
hostname=192.168.1.120
candidate_master=1
port=3306
[server2]
hostname=192.168.1.115
port=3306
candidate_master=1
[server3]
hostname=192.168.1.118
port=3307
3）检查ssh设置
masterha_check_ssh--conf=/etc/masterha/app1.cnf
ln-s /usr/lib/perl5/vendor_perl/MHA /usr/lib64/perl5/vendor_perl/
4）检查主从复制
masterha_check_repl--conf=/etc/masterha/app1.cnf
5）安装keepalived
tar xfkeepalived-1.2.12.tar.gz
cd keepalived-1.2.12
./configure--prefix=/usr/local/keepalived
make&& make install
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/
cp/usr/local/keepalived/sbin/keepalived /usr/sbin/
主库keepalived配置文件
vi/etc/keepalived/keepalived.conf
global_defs {
notification_email {
lihong@bxjinrong.com
}
notification_email_fromAlexandre.Cassen@firewall.loc
smtp_server 127.0.0.1
smtp_connect_timeout 30
router_id MySQL_HA
}
vrrp_instance VI_1{
state BACKUP
interface eth0
virtual_router_id 51
nopreempt
priority 150
advert_int 1
authentication {
auth_type PASS
auth_pass 1111
}
virtual_ipaddress {
192.168.1.20
}
}
备用主库的keepalived配置文件
vi/etc/keepalived/keepalived.conf
global_defs {
notification_email {
lihong@bxjinrong.com
}
notification_email_fromAlexandre.Cassen@firewall.loc
smtp_server 127.0.0.1
smtp_connect_timeout 30
router_id MySQL_HA
}
vrrp_instance VI_1{
state BACKUP
interface eth0
virtual_router_id 51
priority 120
advert_int 1
authentication {
auth_type PASS
auth_pass 1111
}
virtual_ipaddress {
192.168.1.20
}
}
7）mhamanager管理
启动manager
nohupmasterha_manager --conf=/etc/masterha/app1.cnf --remove_dead_master_conf--ignore_last_failover < /dev/null > /var/log/masterha/app1/manager.log2>&1 &
关闭manager
masterha_stop --conf=/etc/masterha/app1.cnf
查看manager的状态
masterha_check_status--conf=/etc/masterha/app1.cnf
切换
1启动manager后，master发生故障后会自动切换
2在线切换过程
masterha_stop --conf=/etc/masterha/app1.cnf
masterha_master_switch--conf=/etc/masterha/app1.cnf --master_state=alive--new_master_host=192.168.1.120 --new_master_port=3306 --orig_master_is_new_slave--running_updates_limit=10000
相关脚本
1）master_ip_failover
#!/usr/bin/envperl
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 $vip= '192.168.1.120';
my$ssh_start_vip = "/etc/init.d/keepalived start";
my$ssh_stop_vip = "/etc/init.d/keepalived stop";
GetOptions(
'command=s' => \$command,
'ssh_user=s' => \$ssh_user,
'orig_master_host=s' =>\$orig_master_host,
'orig_master_ip=s' => \$orig_master_ip,
'orig_master_port=i' =>\$orig_master_port,
'new_master_host=s' => \$new_master_host,
'new_master_ip=s' =>\$new_master_ip,
'new_master_port=i' => \$new_master_port,
);
exit &main();
sub main {
print "\n\nIN SCRIPTTEST====$ssh_stop_vip==$ssh_start_vip===\n\n";
if ( $command eq "stop" ||$command eq "stopssh" ) {
my $exit_code = 1;
eval {
print "Disabling the VIP onold 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 - $vipon 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 thescript.. OK \n";
#`ssh $ssh_user\@cluster1 \"$ssh_start_vip \"`;
exit 0;
}
else {
&usage();
exit 1;
}
}
# A simple systemcall that enable the VIP on the new master
sub start_vip() {
`ssh $ssh_user\@$new_master_host \"$ssh_start_vip \"`;
}
# A simple systemcall that disable the VIP on the old_master
sub stop_vip() {
return 0 unless ($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";
}
2）master_ip_online_change
#!/usr/bin/envperl
# Copyright (C) 2011 DeNA Co.,Ltd.
#
# This program is free software; you canredistribute it and/or modify
# it under the terms of the GNU General PublicLicense as published by
# the Free Software Foundation; either version2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope thatit will be useful,
# but WITHOUT ANY WARRANTY; without even theimplied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULARPURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNUGeneral Public License
# along with this program; if not, write tothe Free Software
# Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston,MA 02110-1301 USA
## Note: This is asample script and is not complete. Modify the script based on your environment.
use strict;
use warnings FATAL=> 'all';
use Getopt::Long;
use MHA::DBHelper;
use MHA::NodeUtil;
use Time::HiResqw( sleep gettimeofday tv_interval );
use Data::Dumper;
my $ssh_user ="root";
my $vip ='192.168.1.20';
my $ssh_start_vip= "/etc/init.d/keepalived start";
my $ssh_stop_vip ="/etc/init.d/keepalived stop";
my $_tstart;
my$_running_interval = 0.1;
my (
$command, $orig_master_host, $orig_master_ip,
$orig_master_port, $orig_master_user,$orig_master_password,
$new_master_host, $new_master_ip, $new_master_port,
$new_master_user, $new_master_password
);
GetOptions(
'command=s' => \$command,
'orig_master_host=s' => \$orig_master_host,
'orig_master_ip=s' => \$orig_master_ip,
'orig_master_port=i' => \$orig_master_port,
'orig_master_user=s' => \$orig_master_user,
'orig_master_password=s' =>\$orig_master_password,
'new_master_host=s' => \$new_master_host,
'new_master_ip=s' => \$new_master_ip,
'new_master_port=i' => \$new_master_port,
'new_master_user=s' => \$new_master_user,
'new_master_password=s' => \$new_master_password,
);
exit &main();
subcurrent_time_us {
my ( $sec, $microsec ) = gettimeofday();
my $curdate = localtime($sec);
return $curdate . " " . sprintf("%06d", $microsec );
}
sub sleep_until {
my $elapsed = tv_interval($_tstart);
if ( $_running_interval > $elapsed ) {
sleep( $_running_interval - $elapsed );
}
}
subget_threads_util {
my $dbh = shift;
my $my_connection_id = shift;
my $running_time_threshold = shift;
my $type = shift;
$running_time_threshold = 0 unless($running_time_threshold);
$type = 0 unless ($type);
my @threads;
my $sth = $dbh->prepare("SHOWPROCESSLIST");
$sth->execute();
while ( my $ref = $sth->fetchrow_hashref()) {
my $id = $ref->{Id};
my $user = $ref->{User};
my $host = $ref->{Host};
my $command = $ref->{Command};
my$state = $ref->{State};
my $query_time = $ref->{Time};
my $info = $ref->{Info};
$info =~ s/^\s*(.*?)\s*$/$1/ ifdefined($info);
next if ( $my_connection_id == $id );
next if ( defined($query_time) &&$query_time < $running_time_threshold );
next if ( defined($command) && $command eq "BinlogDump" );
next if ( defined($user) && $user eq "systemuser" );
next
if ( defined($command)
&& $command eq "Sleep"
&& defined($query_time)
&& $query_time >= 1 );
if ( $type >= 1 ) {
next if ( defined($command) &&$command eq "Sleep" );
next if ( defined($command) &&$command eq "Connect" );
}
if ( $type >= 2 ) {
next if ( defined($info) && $info=~ m/^select/i );
next if ( defined($info) && $info=~ m/^show/i );
}
push @threads, $ref;
}
return @threads;
}
sub main {
if ( $command eq "stop" ) {
## Gracefully killing connections on thecurrent master
# 1. Set read_only= 1 on the new master
# 2. DROP USER so that no app user canestablish new connections
# 3. Set read_only= 1 on the current master
# 4. Kill current queries
# * Any database access failure will resultin script die.
my $exit_code = 1;
eval {
## Setting read_only=1 on the new master(to avoid accident)
my $new_master_handler = newMHA::DBHelper();
# args: hostname, port, user, password,raise_error(die_on_error)_or_not
$new_master_handler->connect($new_master_ip, $new_master_port,
$new_master_user, $new_master_password,1 );
print current_time_us() . " Setread_only on the new master.. ";
$new_master_handler->enable_read_only();
if ($new_master_handler->is_read_only() ) {
print "ok.\n";
}
else {
die "Failed!\n";
}
$new_master_handler->disconnect();
# Connecting to the orig master, die ifany database error happens
my $orig_master_handler = newMHA::DBHelper();
$orig_master_handler->connect($orig_master_ip, $orig_master_port,
$orig_master_user,$orig_master_password, 1 );
## Drop application user so that nobodycan connect. Disabling per-session binlog beforehand
$orig_master_handler->disable_log_bin_local();
print current_time_us() . " Drppingapp user on the orig master..\n";
#FIXME_xxx_drop_app_user($orig_master_handler);
## Waiting for N * 100 milliseconds sothat current connections can exit
my $time_until_read_only = 15;
$_tstart = [gettimeofday];
my @threads = get_threads_util($orig_master_handler->{dbh},
$orig_master_handler->{connection_id} );
while ( $time_until_read_only > 0&& $#threads >= 0 ) {
if ( $time_until_read_only % 5 == 0 ) {
printf
"%s Waitingall running %d threads are disconnected.. (max %d milliseconds)\n",
current_time_us(), $#threads + 1,$time_until_read_only * 100;
if ( $#threads < 5 ) {
print Data::Dumper->new( [$_])->Indent(0)->Terse(1)->Dump . "\n"
foreach (@threads);
}
}
sleep_until();
$_tstart = [gettimeofday];
$time_until_read_only--;
@threads = get_threads_util($orig_master_handler->{dbh},
$orig_master_handler->{connection_id});
}
## Setting read_only=1 on the currentmaster so that nobody(except SUPER) can write
print current_time_us() . " Setread_only=1 on the orig master.. ";
$orig_master_handler->enable_read_only();
if ( $orig_master_handler->is_read_only()) {
print "ok.\n";
}
else {
die "Failed!\n";
}
## Waiting for M * 100 milliseconds sothat current update queries can complete
my $time_until_kill_threads = 5;
@threads = get_threads_util($orig_master_handler->{dbh},
$orig_master_handler->{connection_id} );
while ( $time_until_kill_threads > 0&& $#threads >= 0 ) {
if ( $time_until_kill_threads % 5 == 0) {
printf
"%s Waitingall running %d queries are disconnected.. (max %d milliseconds)\n",
current_time_us(), $#threads + 1,$time_until_kill_threads * 100;
if ( $#threads < 5 ) {
print Data::Dumper->new( [$_])->Indent(0)->Terse(1)->Dump . "\n"
foreach (@threads);
}
}
sleep_until();
$_tstart = [gettimeofday];
$time_until_kill_threads--;
@threads = get_threads_util($orig_master_handler->{dbh},
$orig_master_handler->{connection_id} );
}
print "Disabling the VIP on oldmaster: $orig_master_host \n";
&stop_vip();
## Terminating all threads
print current_time_us() . " Killingall application threads..\n";
$orig_master_handler->kill_threads(@threads) if ( $#threads >= 0);
print current_time_us() . "done.\n";
$orig_master_handler->enable_log_bin_local();
$orig_master_handler->disconnect();
## After finishing the script, MHAexecutes FLUSH TABLES WITH READ LOCK
$exit_code = 0;
};
if ($@) {
warn "Got Error: $@\n";
exit $exit_code;
}
exit $exit_code;
}
elsif ( $command eq "start" ) {
## Activating master ip on the new master
# 1. Create app user with write privileges
# 2. Moving backup script if needed
# 3. Register new master's ip to thecatalog database
# We don't returnerror even though activating updatable accounts/ip failed so that we don'tinterrupt slaves' recovery.
# If exit code is0 or 10, MHA does not abort
my $exit_code = 10;
eval {
my $new_master_handler = newMHA::DBHelper();
# args: hostname, port, user, password,raise_error_or_not
$new_master_handler->connect($new_master_ip, $new_master_port,
$new_master_user, $new_master_password,1 );
## Set read_only=0 on the new master
$new_master_handler->disable_log_bin_local();
print current_time_us() . " Setread_only=0 on the new master.\n";
$new_master_handler->disable_read_only();
## Creating an app user on the new master
print current_time_us() . " Creatingapp user on the new master..\n";
FIXME_xxx_create_app_user($new_master_handler);
$new_master_handler->enable_log_bin_local();
$new_master_handler->disconnect();
## Update master ip on the catalogdatabase, etc
print "Enabling the VIP - $vip onthe new master - $new_master_host \n";
&start_vip();
$exit_code = 0;
};
if ($@) {
warn "Got Error: $@\n";
exit $exit_code;
}
exit $exit_code;
}
elsif ( $command eq "status" ) {
# do nothing
exit 0;
}
else {
&usage();
exit 1;
}
}
# A simple systemcall that enable the VIP on the new master
sub start_vip() {
`ssh $ssh_user\@$new_master_host \"$ssh_start_vip \"`;
}
# A simple systemcall that disable the VIP on the old_master
sub stop_vip() {
`ssh $ssh_user\@$orig_master_host \"$ssh_stop_vip \"`;
}
sub usage {
print
"Usage:master_ip_online_change --command=start|stop|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";
die;
}
MHA测试：
MHA的三种工作情况：
一、自动Failover
必须启动mha Manager监控，否则无法自动切换，切换包括以下步骤：
1、 配置文件检查阶段（包括整个集群的配置文件）
2、 宕机的MASTER处理，这个阶段包括虚拟IP摘除操作，
3、 复制DEAD MASTER和最新SLAVE相差的RELAY LOG，并保存MHA MANAGER具体的目录下
4、 识别含有最新更新的SLAVE
5、 应用从MASTER保存的二进制日志事件
6、 提升一个SLAVE为新的MASTER进行复制
7、 使其他的SLAVE连接新的MASTER进行复制
###在自动切换之后监控就停止了
二、手动切换
1、 不需要开启mha manager监控
2、 如果MHA MANAGER检测到没有DEAD的SERVER将报错，并结束FAILOVER ，所以手动切换必须在主MYSQL宕掉才可以
三、在线进行切换
1、 检测复制设置和确定当前主服务器
2、 确定新的主服务器
3、 阻塞写入到当前主服务器
4、 等待所有从服务器赶上复制
5、 授予写入到新的主服务器
6、 重新设置从服务器
#1、自动识别MASTER和SLAVE问题，VIP的移动
3、 负载均衡问题，当有机器离开集群时，负载比例
四、切换满足条件
1、 所有SLAVE的IO、SQL线程都在运行
2、 所有的SHOW SLAVE STATUS的输出中SECONDS_BEHIND_MASTER参数小于或等于running_updates_limit秒，如果在切换过程中不指定，默认为1秒
3、 在MASTER端，通过SHOW PROCESSLIST输出，没有一个更新花费的时间大于RUNNING
##在线切换需要调用master_ip_online_change这个脚本，貌似这个脚本不够完善，，需要自己修改
软件包下载：
http://down.51cto.com/data/2258543
http://down.51cto.com/data/2258544
本文转自 DBAspace 51CTO博客，原文链接:http://blog.51cto.com/dbaspace/1898371
