作者：刘开洋爱可生交付服务部团队北京 DBA，次要负责解决 MySQL 的 troubleshooting 和我司自研数据库自动化治理平台 DMP 的日常运维问题，对数据库及周边技术有浓重的学习趣味，喜爱看书，谋求技术。
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阐明
本节次要介绍对 secondary_check_script 调用 masterha_secondary_check 脚本的阐明。
[root@yang-03 ~]# cat /usr/bin/masterha_secondary_check#!/usr/bin/env perl···$| = 1;GetOptions( 'help' => \$help, 'version' => \$version, 'secondary_host=s' => \@monitoring_servers, 'user=s' => \$ssh_user, 'port=s' => \$ssh_port, 'options=s' => \$ssh_options, 'master_host=s' => \$master_host, 'master_ip=s' => \$master_ip, 'master_port=i' => \$master_port, 'master_user=s' => \$master_user, 'master_password=s' => \$master_password, 'ping_type=s' => \$ping_type, 'timeout=i' => \$timeout,); if ($version) { print "masterha_secondary_check version $MHA::ManagerConst::VERSION.\n"; exit 0;} if ($help) { pod2usage(0);} unless ($master_host) { pod2usage(1);} sub exit_by_signal { exit 1;}local $SIG{INT} = $SIG{HUP} = $SIG{QUIT} = $SIG{TERM} = \&exit_by_signal; $ssh_user = "root" unless ($ssh_user);$ssh_port = 22 unless ($ssh_port);$master_port = 3306 unless ($master_port); if ($ssh_options) { $MHA::ManagerConst::SSH_OPT_CHECK = $ssh_options;}$MHA::ManagerConst::SSH_OPT_CHECK =~ s/VAR_CONNECT_TIMEOUT/$timeout/; # 0: master is not reachable from all monotoring servers# 1: unknown errors# 2: at least one of monitoring servers is not reachable from this script# 3: master is reachable from at least one of monitoring serversmy $exit_code = 0; foreach my $monitoring_server (@monitoring_servers) { my $ssh_user_host = $ssh_user . '@' . $monitoring_server; my $command ="ssh $MHA::ManagerConst::SSH_OPT_CHECK -p $ssh_port $ssh_user_host \"perl -e " . "\\\"use IO::Socket::INET; my \\\\\\\$sock = IO::Socket::INET->new" . "(PeerAddr => \\\\\\\"$master_host\\\\\\\", PeerPort=> $master_port, " . "Proto =>'tcp', Timeout => $timeout); if(\\\\\\\$sock) { close(\\\\\\\$sock); " . "exit 3; } exit 0;\\\" \""; my $ret = system($command); $ret = $ret >> 8; if ( $ret == 0 ) { print"Monitoring server $monitoring_server is reachable, Master is not reachable from $monitoring_server. OK.\n"; next; } if ( $ret == 3 ) { if ( defined $ping_type && $ping_type eq $MHA::ManagerConst::PING_TYPE_INSERT ) { my $ret_insert; my $command_insert = "ssh $MHA::ManagerConst::SSH_OPT_CHECK -p $ssh_port $ssh_user_host \'" . "/usr/bin/mysql -u$master_user -p$master_password -h$master_host " . "-e \"CREATE DATABASE IF NOT EXISTS infra; " . "CREATE TABLE IF NOT EXISTS infra.chk_masterha (\\`key\\` tinyint NOT NULL primary key,\\`val\\` int(10) unsigned NOT NULL DEFAULT '0'\) engine=InnoDB; " . "INSERT INTO infra.chk_masterha values (1,unix_timestamp()) ON DUPLICATE KEY UPDATE val=unix_timestamp()\"\'"; my $sigalrm_timeout = 3; eval { local $SIG{ALRM} = sub { die "timeout.\n"; }; alarm $sigalrm_timeout; $ret_insert = system($command_insert); $ret_insert = $ret_insert >> 8; alarm 0; }; if ( $@ || $ret_insert != 0 ) { print"Monitoring server $monitoring_server is reachable, Master is not writable from $monitoring_server. OK.\n"; next; } } print "Master is reachable from $monitoring_server!\n"; $exit_code = 3; last; } else { print "Monitoring server $monitoring_server is NOT reachable!\n"; $exit_code = 2; last; }} exit $exit_code;···看到下面的脚本有拍板大，作为一个专一的 DBA，始终谋求着 shell，Perl 语言不熟啊，细看之后发现与 shell 脚本有殊途同归之妙，从相应的正文中，咱们找到了该查看脚本的返回值，即 0,1,2,3，别离代表的含意如下：
# 0: master is not reachable from all monotoring servers# 1: unknown errors# 2: at least one of monitoring servers is not reachable from this script# 3: master is reachable from at least one of monitoring servers上面就让咱们做几个测试领会领会吧。
验证
本试验应用 iptables 进行网络故障场景的模仿，以下图中四条链路是否连通来进行测试，查看对应监控脚本的返回值是否和下面讲的统一。
查看命令：
shell > masterha_secondary_check -s remote_host1 -s remote_host2 .. --user=root --master_host=master_ip --master_ip=master_ip --master_port=3306 --master_user=mha --master_password=*** --ping_type=SELECTtest 1
output：
Master is reachable from remote_host1!
test 2
output：
Master is reachable from remote_host1!
test 3
output：
ssh: connect to host remote_host1 port 22: Connection timed out.
Monitoring server remote_host1 is NOT reachable!
test 4
output：
Master is reachable from remote_host1!
test 5
output：
Monitoring server remote_host1 is reachable, Master is not reachable from remote_host1. OK.
Master is reachable from remote_host2!
test 6
output：
ssh: connect to host remote_host1 port 22: Connection timed out.
Monitoring server remote_host1 is NOT reachable!
test 7
output：
当输出的命令有误时，即合乎 unknown errors，返回值为 1。
test 8
output：
Monitoring server remote_host1 is reachable, Master is not reachable from remote_host1. OK.
Monitoring server remote_host2 is reachable, Master is not reachable from remote_host2. OK.
PS：这里有一个问题，在应用监控服务器 slave 查看主从之间网络连通性时，masterha_secondary_check 脚本对监控主机的应用存在优先级，它会优先应用 remote_host1，如果 remote_host1 与 master 之间网络不同，才会应用 remote_host2 查看与 master 之间的网络连通性。
总结
通过测试验证，发现 MHA 通过调用 secondary_check_script 参数对于网络问题具备肯定的容忍能力，只是相干文档形容过于简略，如需持续应用，须要一直进行验证测试，总体来讲，MHA 的性能还是及其弱小的。