《叶问》38期，MGR整个集群挂掉后，如何才能自动选主，不用手动干预

[root@GreatSQL ~]# cat /usr/lib/systemd/system/greatsql.service
...
Restart=on-failure

[root@GreatSQL ~]# mysqlsh --uri greatsql@yejr-mgr3:3306
...
-- 不管干啥，都先看 help，这是玩转Linux的必备素养，啥事不清楚都先找男人（man）
-- 注意到有这样的一个方法 rebootClusterFromCompleteOutage()，看起来没跑了


MySQL  yejr-mgr3:3306 ssl  JS > \help dba
      rebootClusterFromCompleteOutage([clusterName][, options])
            Brings a cluster back ONLINE when all members are OFFLINE.

-- 跑一个试试看
MySQL  yejr-mgr3:3306 ssl  JS > dba.rebootClusterFromCompleteOutage()
Restoring the default cluster from complete outage...

The instance 'yejr-mgr4:3306' was part of the cluster configuration.
Would you like to rejoin it to the cluster? [y/N]: y

The instance 'yejr-mgr2:3306' was part of the cluster configuration.
Would you like to rejoin it to the cluster? [y/N]: y

Dba.rebootClusterFromCompleteOutage: The active session instance (yejr-mgr3:3306) isn't the most updated in comparison with the ONLINE instances of the Cluster's metadata. Please use the most up to date instance: 'yejr-mgr4:3306'. (RuntimeError)

[root@GreatSQL ~]# mysqlsh --uri greatsql@yejr-mgr3:3306
...
MySQL  yejr-mgr4:3306 ssl  JS > dba.rebootClusterFromCompleteOutage()
Restoring the default cluster from complete outage...

The instance 'yejr-mgr3:3306' was part of the cluster configuration.
Would you like to rejoin it to the cluster? [y/N]: y

The instance 'yejr-mgr2:3306' was part of the cluster configuration.
Would you like to rejoin it to the cluster? [y/N]: y

yejr-mgr4:3306 was restored.
Rejoining 'yejr-mgr3:3306' to the cluster.
Rejoining instance 'yejr-mgr3:3306' to cluster 'GreatSQLMGR'...
The instance 'yejr-mgr3:3306' was successfully rejoined to the cluster.

Rejoining 'yejr-mgr2:3306' to the cluster.
Rejoining instance 'yejr-mgr2:3306' to cluster 'GreatSQLMGR'...
The instance 'yejr-mgr2:3306' was successfully rejoined to the cluster.

The cluster was successfully rebooted.

-- yejr-mgr2节点
root@GreatSQL [none]> select RECEIVED_TRANSACTION_SET from performance_schema.replication_connection_status where 
channel_name = 'group_replication_applier' union all 
select variable_value from performance_schema.global_variables where 
variable_name = 'gtid_executed'\G
*************************** 1. row ***************************
RECEIVED_TRANSACTION_SET:
*************************** 2. row ***************************
RECEIVED_TRANSACTION_SET: 1c293e90-3bdc-11ec-bca1-525400e2078a:1-4537605,
4b7b3b88-3b13-11ec-86e9-525400e2078a:1

-- yejr-mgr3节点
...
*************************** 1. row ***************************
RECEIVED_TRANSACTION_SET:
*************************** 2. row ***************************
RECEIVED_TRANSACTION_SET: 1c293e90-3bdc-11ec-bca1-525400e2078a:1-4542304,
4b7b3b88-3b13-11ec-86e9-525400e2078a:1

-- yejr-mgr4节点
...
*************************** 1. row ***************************
RECEIVED_TRANSACTION_SET:
*************************** 2. row ***************************
RECEIVED_TRANSACTION_SET: 1c293e90-3bdc-11ec-bca1-525400e2078a:1-4652391,
4b7b3b88-3b13-11ec-86e9-525400e2078a:1

[root@GreatSQL ~]# mysql -hyejr-mgr4 -P3306 -ugreatsql -p
...
greatsql@mgr4:3306 [(none)]>set global group_replication_bootstrap_group=ON;

greatsql@mgr4:3306 [(none)]>start group_replication;

-- 启动完MGR后，记得立即将其设置为OFF
greatsql@mgr4:3306 [(none)]>set global group_replication_bootstrap_group=OFF;

--directory dir_path, -d dir_path

Specifies that a self-contained MySQL Router installation will be created at the defined directory instead of configuring the system-wide router instance. This also allows multiple router instances to be created on the same system.

-- 针对4306端口的服务，初始化一个router实例
-- 可自行指定目录、实例名、端口号等多个选项
mysqlrouter --bootstrap mymgr@172.16.16.16:4306 --name=MyMGR --directory=/etc/mysqlrouter/MyMGR  --user=mysqlrouter --conf-base-port=7446 --https-port=9443

$path/start.sh
$path/stop.sh
$path/mysqlrouter.pid
$path/mysqlrouter.conf
$path/mysqlrouter.key
$path/run
$path/run/keyring
$path/data
$path/log
$path/log/mysqlrouter.log

[root@yejr-mgr4 ~]# ls -l /usr/lib/systemd/system/mysqlrouter@*
-rw-r--r-- 1 root root 312 Nov 11 14:13 /usr/lib/systemd/system/mysqlrouter@GrMGR.service
-rw-r--r-- 1 root root 312 Nov 11 14:12 /usr/lib/systemd/system/mysqlrouter@MyMGR.service

-- 查看其中一个文件的内容
[root@yejr-mgr2 ~]# cat /usr/lib/systemd/system/mysqlrouter@GrMGR.service
[Unit]
Description=MySQL Router
After=network.target
After=syslog.target
[Service]
Type=notify
User=mysqlrouter
Group=mysqlrouter
ExecStart=/usr/bin/mysqlrouter -c /etc/mysqlrouter/GrMGR/mysqlrouter.conf
LimitNOFILE = 10000
#Restart=on-failure
Restart=always
PrivateTmp=true
[Install]
WantedBy=multi-user.target

pager cat - | sed -n "/^TRANSACTIONS$/,/^FILE I\/O$/p"