1.背景

MySQL Group Replication（MGR）是MySQL官方在5.7.17版本引进的一个数据库高可用与高扩展的解决方案，以插件形式提供，实现了分布式下数据的最终一致性，总结MGR特点如下：

* 高一致性：基于分布式paxos协议实现组复制，保证数据一致性；

* 高容错性：自动检测机制，只要不是大多数节点都宕机就可以继续工作，内置防脑裂保护机制；

* 高扩展性：节点的增加与移除会自动更新组成员信息，新节点加入后，自动从其他节点同步增量数据，直到与其他节点数据一致；

* 高灵活性：提供单主模式和多主模式，单主模式在主库宕机后能够自动选主，所有写入都在主节点进行，多主模式支持多节点写入。

2. 环境：

3台服务器搭建3节点MGR集群，MySQL版本5.7.27，操作系统版本CentOS 7.3。

* 192.168.8.71

* 192.168.8.72

* 192.168.8.73

3.安装步骤

3.1 安装MySQL5.7

MySQL官方版5.7.27，采用Linux Generic安装方式，直接下载压缩包，解压到目录/usr/local/mysql。

3.2 修改配置文件

编辑配置文件/etc/my.cnf，3个节点除了server_id、loose-group_replication_local_address、report_host 三个参数不一样外，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 初始化数据库（所有节点执行）

略

3.4 启动数据库，安装MGR插件，设置复制账号（所有节点执行）

--安装MGR插件

mysql>INSTALL PLUGIN group_replication SONAME 'group_replication.so';

--设置复制账号

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 启动MGR单主模式

# 启动MGR，在主库(192.168.8.71)上执行

mysql> SET GLOBAL group_replication_bootstrap_group=ON;

mysql> START GROUP_REPLICATION;

mysql> SET GLOBAL group_replication_bootstrap_group=OFF;

# 查看MGR组信息

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)

# 其他节点加入MGR，在从库（192.168.8.72，192.168.8.73）上执行

mysql> START GROUP_REPLICATION;

# 查看MGR组信息

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个节点状态为online，并且主节点为192.168.8.71，只有主节点可以写入，其他节点只读，MGR单主模式搭建成功

3.6 切换到多主模式

MGR切换模式需要重新启动组复制，因些需要在所有节点上先关闭组复制，设置 group_replication_single_primary_mode=OFF 等参数，再启动组复制。

# 停止组复制(所有节点执行)：

mysql> stop group_replication;

mysql> set global group_replication_single_primary_mode=OFF;

mysql> set global group_replication_enforce_update_everywhere_checks=ON;

# 随便选择某个节点执行

mysql> SET GLOBAL group_replication_bootstrap_group=ON;

mysql> START GROUP_REPLICATION;

mysql> SET GLOBAL group_replication_bootstrap_group=OFF;

# 其他节点执行

mysql> START GROUP_REPLICATION;

# 查看组信息，所有节点的 MEMBER_ROLE 都为 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)

可以看到所有节点状态都是online，角色都是PRIMARY，MGR多主模式搭建成功。

3.7 切回单主模式

# 所有节点执行

mysql> stop group_replication;

mysql> set global group_replication_enforce_update_everywhere_checks=OFF;

mysql> set global group_replication_single_primary_mode=ON;

# 主节点（192.168.8.71）执行

SET GLOBAL group_replication_bootstrap_group=ON;

START GROUP_REPLICATION;

SET GLOBAL group_replication_bootstrap_group=OFF;

# 从节点（192.168.8.72、192.168.8.73）执行

START GROUP_REPLICATION;

# 查看MGR组信息

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|

+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+