MySQL MGR 叢集搭建（單主模式）
MySQL Group Replication（MGR）是MySQL官方在5.7.17版本引進的一個數據庫高可用與高擴充套件的解決方案，以外掛形式提供，實現了分散式下資料的最終一致性，總結MGR特點如下：
* 高一致性：基於分散式paxos協議實現組複製，保證資料一致性；
* 高容錯性：自動檢測機制，只要不是大多數節點都宕機就可以繼續工作，內建防腦裂保護機制；
* 高擴充套件性：節點的增加與移除會自動更新組成員資訊，新節點加入後，自動從其他節點同步增量資料，直到與其他節點資料一致；
* 高靈活性：提供單主模式和多主模式，單主模式在主庫宕機後能夠自動選主，所有寫入都在主節點進行，多主模式支援多節點寫入。
2. 環境：
3臺伺服器搭建3節點MGR叢集，MySQL版本5.7.27，作業系統版本CentOS 7.3。
* 192.168.8.71
* 192.168.8.72
* 192.168.8.73
3.安裝步驟
3.1 安裝MySQL5.7
MySQL官方版5.7.27，採用Linux Generic安裝方式，直接下載壓縮包，解壓到目錄/usr/local/mysql。
3.2 修改配置檔案
編輯配置檔案/etc/my.cnf，3個節點除了server_id、loose-group_replication_local_address、report_host 三個引數不一樣外，其他保持一致。
[mysqld]
port=3306
basedir=/usr/local/mysql
datadir=/usr/local/mysql/data
server_id=1
gtid_mode=ON
enforce_gtid_consistency=ON
binlog_checksum=NONE
log_bin=binlog
log_slave_updates=ON
binlog_format=ROW
master_info_repository=TABLE
relay_log_info_repository=TABLE
transaction_write_set_extraction=XXHASH64
loose-group_replication_group_name="aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"
loose-group_replication_start_on_boot=OFF
loose-group_replication_local_address= "192.168.8.71:33061"
loose-group_replication_group_seeds= "192.168.8.71:33061,192.168.8.72:33061,192.168.8.73:33061"
loose-group_replication_bootstrap_group=OFF
report_host=192.168.8.71
report_port=3306
3.3 初始化資料庫（所有節點執行）
略
3.4 啟動資料庫，安裝MGR外掛，設定複製賬號（所有節點執行）
--安裝MGR外掛
mysql>INSTALL PLUGIN group_replication SONAME 'group_replication.so';
--設定複製賬號
mysql> SET SQL_LOG_BIN=0;
mysql> CREATE USER repl@'%' IDENTIFIED BY 'repl';
mysql> GRANT REPLICATION SLAVE ON *.* TO repl@'%';
mysql> FLUSH PRIVILEGES;
mysql> SET SQL_LOG_BIN=1;
mysql> CHANGE MASTER TO MASTER_USER='repl', MASTER_PASSWORD='repl' FOR CHANNEL 'group_replication_recovery';
3.5 啟動MGR單主模式
# 啟動MGR，在主庫(192.168.8.71)上執行
mysql> SET GLOBAL group_replication_bootstrap_group=ON;
mysql> START GROUP_REPLICATION;
mysql> SET GLOBAL group_replication_bootstrap_group=OFF;
# 檢視MGR組資訊
mysql> SELECT * FROM performance_schema.replication_group_members;
+---------------------------+--------------------------------------+--------------+-------------+--------------+
| CHANNEL_NAME | MEMBER_ID | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+--------------+-------------+--------------+
| group_replication_applier | 7777f2fe-bd6b-11e9-aad5-08002789d401 | 192.168.8.71 | 3306 | ONLINE |
+---------------------------+--------------------------------------+--------------+-------------+--------------+
1 row in set (0.00 sec)
# 其他節點加入MGR，在從庫（192.168.8.72，192.168.8.73）上執行
mysql> START GROUP_REPLICATION;
# 檢視MGR組資訊
mysql> SELECT channel_name,
-> member_id,
-> member_host,
-> member_port,
-> member_state,
-> IF(global_status.variable_name IS NOT NULL, 'PRIMARY', 'SECONDARY') AS member_role
-> FROM performance_schema.replication_group_members
-> LEFT JOIN performance_schema.global_status
-> ON global_status.variable_name = 'group_replication_primary_member'
-> AND global_status.variable_value = replication_group_members.member_id;
+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+
| channel_name | member_id | member_host | member_port | member_state | member_role |
+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+
| group_replication_applier | 7777f2fe-bd6b-11e9-aad5-08002789d401 | 192.168.8.71 | 3306 | ONLINE | PRIMARY |
| group_replication_applier | 7777f2fe-bd6b-11e9-aad5-08002789d402 | 192.168.8.72 | 3306 | ONLINE | SECONDARY |
| group_replication_applier | 7777f2fe-bd6b-11e9-aad5-08002789d403 | 192.168.8.73 | 3306 | ONLINE | SECONDARY |
+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+
3 rows in set (0.00 sec)
可以看到，3個節點狀態為online，並且主節點為192.168.8.71，只有主節點可以寫入，其他節點只讀，MGR單主模式搭建成功
3.6 切換到多主模式
MGR切換模式需要重新啟動組複製，因些需要在所有節點上先關閉組複製，設定 group_replication_single_primary_mode=OFF 等引數，再啟動組複製。
# 停止組複製(所有節點執行)：
mysql> stop group_replication;
mysql> set global group_replication_single_primary_mode=OFF;
mysql> set global group_replication_enforce_update_everywhere_checks=ON;
# 隨便選擇某個節點執行
mysql> SET GLOBAL group_replication_bootstrap_group=ON;
mysql> START GROUP_REPLICATION;
mysql> SET GLOBAL group_replication_bootstrap_group=OFF;
# 其他節點執行
mysql> START GROUP_REPLICATION;
# 檢視組資訊，所有節點的 MEMBER_ROLE 都為 PRIMARY
mysql> SELECT channel_name,
-> member_id,
-> member_host,
-> member_port,
-> member_state,
-> IF(global_status.variable_name IS NOT NULL, 'PRIMARY', 'SECONDARY') AS member_role
-> FROM performance_schema.replication_group_members
-> LEFT JOIN performance_schema.global_status
-> ON global_status.variable_name = 'group_replication_primary_member'
-> AND global_status.variable_value = replication_group_members.member_id;
+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+
| channel_name | member_id | member_host | member_port | member_state | member_role |
+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+
| group_replication_applier | 7777f2fe-bd6b-11e9-aad5-08002789d401 | 192.168.8.71 | 3306 | ONLINE | PRIMARY |
| group_replication_applier | 7777f2fe-bd6b-11e9-aad5-08002789d402 | 192.168.8.72 | 3306 | ONLINE | PRIMARY |
| group_replication_applier | 7777f2fe-bd6b-11e9-aad5-08002789d403 | 192.168.8.73 | 3306 | ONLINE | PRIMARY |
+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+
3 rows in set (0.00 sec)http://www.chacha8.cn/detail/1132398239.html
可以看到所有節點狀態都是online，角色都是PRIMARY，MGR多主模式搭建成功。
3.7 切回單主模式
# 所有節點執行
mysql> stop group_replication;
mysql> set global group_replication_enforce_update_everywhere_checks=OFF;
mysql> set global group_replication_single_primary_mode=ON;
# 主節點（192.168.8.71）執行
SET GLOBAL group_replication_bootstrap_group=ON;
START GROUP_REPLICATION;
SET GLOBAL group_replication_bootstrap_group=OFF;
# 從節點（192.168.8.72、192.168.8.73）執行
START GROUP_REPLICATION;
# 檢視MGR組資訊
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mysql> SELECT channel_name,
-> member_id,
-> member_host,
-> member_port,
-> member_state,
-> IF(global_status.variable_name IS NOT NULL, 'PRIMARY', 'SECONDARY') AS member_role
-> FROM performance_schema.replication_group_members
-> LEFT JOIN performance_schema.global_status
-> ON global_status.variable_name = 'group_replication_primary_member'
-> AND global_status.variable_value = replication_group_members.member_id;
+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+
| channel_name | member_id | member_host | member_port | member_state | member_role |
+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+
| group_replication_applier | 7777f2fe-bd6b-11e9-aad5-08002789d401 | 192.168.8.71 | 3306 | ONLINE | PRIMARY |
| group_replication_applier | 7777f2fe-bd6b-11e9-aad5-08002789d402 | 192.168.8.72 | 3306 | ONLINE | SECONDARY |
| group_replication_applier | 7777f2fe-bd6b-11e9-aad5-08002789d403 | 192.168.8.73 | 3306 | ONLINE | SECONDARY |
+---------------------------+--------------------------------------+--------------+-------------+--------