MGR主备集群实现异步连接故障转移的步骤_诺佳网—

1.概述

MySQL 8.0.22 开始，支持异步连接故障切换机制，在现有主从复制连接失败后，自动建立到新主的异步复制连接。

MySQL 8.0.23 开始，异步连接故障切换机制还支持组复制拓扑，通过自动监视组成员身份的更改并区分主节点和从节点，在组复制主节点故障选出新主节点后，自动建立到新主的异步复制连接。

MySQL 8.0.26 开始，组复制可以设置组成员在特定情况下采取的操作，比如成员操作 mysql_disable_super_read_only_if_primary 当选择一个新的primary时，使处于单主模式的组保持超级只读模式，这样该组只接受复制的事务，不接受来自客户端的任何直接写操作。

MySQL 8.0.27 开始，异步连接故障切换机制还允许组复制作为副本，组的主节点发生故障时，新的主节点自动重新连接到源端。新增成员操作mysql_start_failover_channels_if_primary，默认情况下，此成员操作是启用的，当启用此成员动作时，在"CHANGE replication SOURCE TO"语句中为复制通道设置SOURCE_CONNECTION_AUTO_FAILOVER=1时，组复制主节点复制通道上的异步连接故障转移将激活。

2.架构

MGR B 作为 MGR A 的备份

本次测试通过搭建2套MGR作为主备集群，进行异步连接故障切换测试：

（1）当主集群MGR A 的主节点发生故障时，备集群MGR B的主节点能够实现异步故障转移，自动连接MGR A 的新主节点，主备集群同步不断开，实现数据正常同步。

（2）当备集群MGR B 的主节点发生故障时，MGR B 的新主节点能够自动启动复制通道，自动连接MGR A 主节点，主备集群同步不断开，实现数据正常同步。

（3）设置MGR B成员行为，使处于单主模式的组 MGR B 保持超级只读模式，这样该组只接受复制的事务，不接受来自客户端的任何直接写。

3.测试

本次测试基于 MySQL 8.0.31，搭建2套MGR集群（单主模式）

3.1 搭建MGR集群

MGR A：

mysql>select*fromperformance_schema.replication_group_members;
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|CHANNEL_NAME|MEMBER_ID|MEMBER_HOST|MEMBER_PORT|MEMBER_STATE|MEMBER_ROLE|MEMBER_VERSION|MEMBER_COMMUNICATION_STACK|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|group_replication_applier|44921323-bd95-11ed-8db5-00163e01f842|172.17.140.201|6002|ONLINE|SECONDARY|8.0.31|XCom|
|group_replication_applier|6f904c5c-bd95-11ed-bc79-00163e01f842|172.17.140.201|6003|ONLINE|SECONDARY|8.0.31|XCom|
|group_replication_applier|c9e254d3-bd94-11ed-8ae9-00163e01f842|172.17.140.201|6001|ONLINE|PRIMARY|8.0.31|XCom|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
3rowsinset(0.01sec)

MGR B：

select*fromperformance_schema.replication_group_members;
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|CHANNEL_NAME|MEMBER_ID|MEMBER_HOST|MEMBER_PORT|MEMBER_STATE|MEMBER_ROLE|MEMBER_VERSION|MEMBER_COMMUNICATION_STACK|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|group_replication_applier|190f4674-be4a-11ed-9452-00163ea5c598|172.17.140.252|6005|ONLINE|PRIMARY|8.0.31|XCom|
|group_replication_applier|3fa9e064-be4a-11ed-92c7-00163ea5c598|172.17.140.252|6006|ONLINE|SECONDARY|8.0.31|XCom|
|group_replication_applier|6a9691c6-be4a-11ed-8a32-00163ea5c598|172.17.140.252|6007|ONLINE|SECONDARY|8.0.31|XCom|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
3rowsinset(0.00sec)

3.2 创建复制用户

在MGR A 的主节点创建用于复制的用户 repl_user

createuserrepl_user@'%'identifiedwithmysql_native_passwordby'abc123';
grantreplicationslaveon*.*torepl_user@'%';
grantselectonperformance_schema.*torepl_user@'%';

注意：这里复制用户需要有 performance_schema 库的select权限，主要用于获取MGR A集群成员的状态，如果没有这个权限，将不能进行异步连接故障转移。

3.3停止MGR B的组复制

在MGR B的所有节点停止组复制，可先停止从节点，避免发生节点切换

mysql>stopgroup_replication;

注意：这里停止组复制是为了下一步创建异步复制通道，如果不停止复制通道，在运行正常的MGR B 的主节点执行创建复制通道的语句，会导致从节点退出组，报如下错误：

2023-03-09T1451.933981+08:0017887[ERROR][MY-013786][Repl]UnabletosetSOURCE_CONNECTION_AUTO_FAILOVERonanon-existentormisconfiguredreplicationchannel'mgra_to_mgrb',pleasecreatethechannelandrejointheservertothegroup.
2023-03-09T1451.934259+08:0017887[ERROR][MY-013487][Repl]Plugingroup_replicationreported:'AmessagesentthroughtheGroupReplicationmessagedeliverservicewasnotdeliveredsuccessfully.Theserverwillnowleavethegroup.Trytoaddtheserverbacktothegroupandcheckiftheproblempersists,orcheckpreviousmessagesinthelogforhintsofwhatcouldbetheproblem.'
2023-03-09T1451.934704+08:0017887[ERROR][MY-011712][Repl]Plugingroup_replicationreported:'Theserverwasautomaticallysetintoreadonlymodeafteranerrorwasdetected.'
2023-03-09T1455.166405+08:000[System][MY-011504][Repl]Plugingroup_replicationreported:'Groupmembershipchanged:Thismemberhasleftthegroup.'

3.4创建异步复制通道

在MGR B的所有节点创建异步复制通道

changereplicationsourcetosource_host='172.17.140.201',source_port=6001,source_user='repl_user',source_password='abc123',source_auto_position=1,source_connection_auto_failover=1,source_connect_retry=10,source_retry_count=3forchannel'mgra_to_mgrb';

source_host：MGR A 主节点的IP

source_port：MGR A 主节点的端口

source_connection_auto_failover=1：表示开启自动故障转移功能。

source_connect_retry：指定复制副本在与源端的连接超时后重新连接尝试之间的间隔（秒）。

source_retry_count：设置复制副本在连接到源超时后进行的最大重新连接尝试次数。

3.5配置复制源

在MGR B 的主节点配置复制源

selectasynchronous_connection_failover_add_managed('mgra_to_mgrb','GroupReplication','bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb','172.17.140.201',6001,'',90,50);
+-------------------------------------------------------------------------------------------------------------------------------------------------------+
|asynchronous_connection_failover_add_managed('mgra_to_mgrb','GroupReplication','bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb','172.17.140.201',6001,'',90,50)|
+-------------------------------------------------------------------------------------------------------------------------------------------------------+
|TheUDFasynchronous_connection_failover_add_managed()executedsuccessfully.|
+-------------------------------------------------------------------------------------------------------------------------------------------------------+
1rowinset(0.02sec)

语法：

asynchronous_connection_failover_add_managed(channel,managed_type,managed_name,host,port,network_namespace,primary_weight,secondary_weight)

参数：

channel：上面创建的复制通道名称；

managed_type：管理服务的类型，当前可传入的值必须是GroupReplication；

managed_name：管理组的识别符，即group_replication_group_name参数的值；

host：源端主机名；

port：源端端口号；

network_namespace：预留为将来使用，置空；

primary_weight：MGR主服务器的权重，值为1到100，值越大，优先级越高；

secondary_weight：MGR从服务器的权重，值为1到100，值越大，优先级越高；

3.6查看配置的用于异步连接切换的复制源

mysql>select*fromperformance_schema.replication_asynchronous_connection_failover;
+--------------+----------------+------+-------------------+--------+--------------------------------------+
|CHANNEL_NAME|HOST|PORT|NETWORK_NAMESPACE|WEIGHT|MANAGED_NAME|
+--------------+----------------+------+-------------------+--------+--------------------------------------+
|mgra_to_mgrb|172.17.140.201|6001||50|bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb|
+--------------+----------------+------+-------------------+--------+--------------------------------------+
1rowinset(0.00sec)

这里只显示刚才配置的一个节点，启动异步复制通道后就能看到MGR A所有节点。

3.7启动 MGR B 组复制

在MGR B 的主节点重新引导启动组复制

#选一个节点作为引导节点
setglobalgroup_replication_bootstrap_group=ON;
startgroup_replication;
setglobalgroup_replication_bootstrap_group=OFF;

#其余节点启动组复制
startgroup_replication;

#查看MGRB集群状态
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|CHANNEL_NAME|MEMBER_ID|MEMBER_HOST|MEMBER_PORT|MEMBER_STATE|MEMBER_ROLE|MEMBER_VERSION|MEMBER_COMMUNICATION_STACK|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|group_replication_applier|190f4674-be4a-11ed-9452-00163ea5c598|172.17.140.252|6005|ONLINE|PRIMARY|8.0.31|XCom|
|group_replication_applier|3fa9e064-be4a-11ed-92c7-00163ea5c598|172.17.140.252|6006|ONLINE|SECONDARY|8.0.31|XCom|
|group_replication_applier|6a9691c6-be4a-11ed-8a32-00163ea5c598|172.17.140.252|6007|ONLINE|SECONDARY|8.0.31|XCom|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
3rowsinset(0.00sec)

3.8启动异步复制通道

在MGR B的主节点启动

mysql>startreplicaforchannel'mgra_to_mgrb';
mysql>showreplicastatusG
***************************1.row***************************
Replica_IO_State:Waitingforsourcetosendevent
Source_Host:172.17.140.201
Source_User:repl_user
Source_Port:6001
Connect_Retry:10
Source_Log_File:binlog.000001
Read_Source_Log_Pos:2614
Relay_Log_File:relaylog-mgra_to_mgrb.000002
Relay_Log_Pos:2816
Relay_Source_Log_File:binlog.000001
Replica_IO_Running:Yes
Replica_SQL_Running:Yes
Replicate_Do_DB:

异步复制通道运行正常，至此MGR A 与 MGR B已建立主备关系，MGR A主节点与 MGR B 主节点建立异步复制通道。

3.9查看配置的用于异步连接切换的复制源

mysql>select*fromperformance_schema.replication_asynchronous_connection_failover;
+--------------+----------------+------+-------------------+--------+--------------------------------------+
|CHANNEL_NAME|HOST|PORT|NETWORK_NAMESPACE|WEIGHT|MANAGED_NAME|
+--------------+----------------+------+-------------------+--------+--------------------------------------+
|mgra_to_mgrb|172.17.140.201|6001||90|bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb|
|mgra_to_mgrb|172.17.140.201|6002||50|bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb|
|mgra_to_mgrb|172.17.140.201|6003||50|bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb|
+--------------+----------------+------+-------------------+--------+--------------------------------------+
3rowsinset(0.01sec)

可以看到这里显示了 MGR A的所有节点信息，weight 最高的为主节点

3.10故障模拟：主集群MGR A 的主节点发生故障

（1）查看当前MGR A 信息

mysql>select*fromperformance_schema.replication_group_members;
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|CHANNEL_NAME|MEMBER_ID|MEMBER_HOST|MEMBER_PORT|MEMBER_STATE|MEMBER_ROLE|MEMBER_VERSION|MEMBER_COMMUNICATION_STACK|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|group_replication_applier|44921323-bd95-11ed-8db5-00163e01f842|172.17.140.201|6002|ONLINE|SECONDARY|8.0.31|XCom|
|group_replication_applier|6f904c5c-bd95-11ed-bc79-00163e01f842|172.17.140.201|6003|ONLINE|SECONDARY|8.0.31|XCom|
|group_replication_applier|c9e254d3-bd94-11ed-8ae9-00163e01f842|172.17.140.201|6001|ONLINE|PRIMARY|8.0.31|XCom|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
3rowsinset(0.00sec)

当前MGR A 主节点为 6001

（2）查看异步复制信息

登录MGR B 主节点查看

mysql>showreplicastatusG
***************************1.row***************************
Replica_IO_State:Waitingforsourcetosendevent
Source_Host:172.17.140.201
Source_User:repl_user
Source_Port:6001
Connect_Retry:10
Source_Log_File:binlog.000001
Read_Source_Log_Pos:2614
Relay_Log_File:relaylog-mgra_to_mgrb.000002
Relay_Log_Pos:2816
Relay_Source_Log_File:binlog.000001
Replica_IO_Running:Yes
Replica_SQL_Running:Yes
Replicate_Do_DB:

当前MGR B主节点连接的是 MGR A的主节点 6001

（3）模拟MGR A故障

在MGR A主节点执行切主命令，模拟MGR A主节点故障，将6002设置为新主节点

mysql>selectgroup_replication_set_as_primary('44921323-bd95-11ed-8db5-00163e01f842');
+--------------------------------------------------------------------------+
|group_replication_set_as_primary('44921323-bd95-11ed-8db5-00163e01f842')|
+--------------------------------------------------------------------------+
|Primaryserverswitchedto:44921323-bd95-11ed-8db5-00163e01f842|
+--------------------------------------------------------------------------+
1rowinset(0.04sec)

mysql>select*fromperformance_schema.replication_group_members;
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|CHANNEL_NAME|MEMBER_ID|MEMBER_HOST|MEMBER_PORT|MEMBER_STATE|MEMBER_ROLE|MEMBER_VERSION|MEMBER_COMMUNICATION_STACK|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|group_replication_applier|44921323-bd95-11ed-8db5-00163e01f842|172.17.140.201|6002|ONLINE|PRIMARY|8.0.31|XCom|
|group_replication_applier|6f904c5c-bd95-11ed-bc79-00163e01f842|172.17.140.201|6003|ONLINE|SECONDARY|8.0.31|XCom|
|group_replication_applier|c9e254d3-bd94-11ed-8ae9-00163e01f842|172.17.140.201|6001|ONLINE|SECONDARY|8.0.31|XCom|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
3rowsinset(0.00sec)

（4）查看异步复制信息

登录MGR B 主节点查看

mysql>showreplicastatusG
***************************1.row***************************
Replica_IO_State:Waitingforsourcetosendevent
Source_Host:172.17.140.201
Source_User:repl_user
Source_Port:6002
Connect_Retry:10
Source_Log_File:binlog.000001
Read_Source_Log_Pos:3343
Relay_Log_File:relaylog-mgra_to_mgrb.000003
Relay_Log_Pos:435
Relay_Source_Log_File:binlog.000001
Replica_IO_Running:Yes
Replica_SQL_Running:Yes
Replicate_Do_DB:

可以看到MGR B主节点已经自动进行异步连接故障转移，与MGR A新主节点6002建立连接并且连接正常，在此过程中并不需要人为去操作。

3.11故障模拟：备集群MGR B 的主节点发生故障

（1）查看当前MGR B信息

mysql>select*fromperformance_schema.replication_group_members;
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|CHANNEL_NAME|MEMBER_ID|MEMBER_HOST|MEMBER_PORT|MEMBER_STATE|MEMBER_ROLE|MEMBER_VERSION|MEMBER_COMMUNICATION_STACK|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|group_replication_applier|190f4674-be4a-11ed-9452-00163ea5c598|172.17.140.252|6005|ONLINE|PRIMARY|8.0.31|XCom|
|group_replication_applier|3fa9e064-be4a-11ed-92c7-00163ea5c598|172.17.140.252|6006|ONLINE|SECONDARY|8.0.31|XCom|
|group_replication_applier|6a9691c6-be4a-11ed-8a32-00163ea5c598|172.17.140.252|6007|ONLINE|SECONDARY|8.0.31|XCom|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
3rowsinset(0.03sec)

（2）查看异步复制信息

登录MGR B主节点6005

mysql>showreplicastatusG
***************************1.row***************************
Replica_IO_State:Waitingforsourcetosendevent
Source_Host:172.17.140.201
Source_User:repl_user
Source_Port:6002
Connect_Retry:10
Source_Log_File:binlog.000001
Read_Source_Log_Pos:3343
Relay_Log_File:relaylog-mgra_to_mgrb.000003
Relay_Log_Pos:435
Relay_Source_Log_File:binlog.000001
Replica_IO_Running:Yes
Replica_SQL_Running:Yes
Replicate_Do_DB:

当前MGR B主节点与MGR A新主节点6002 异步复制连接正常

登录MGR B从节点6006

mysql>showreplicastatusG
***************************1.row***************************
Replica_IO_State:
Source_Host:172.17.140.201
Source_User:repl_user
Source_Port:6001
Connect_Retry:10
Source_Log_File:
Read_Source_Log_Pos:4
Relay_Log_File:relaylog-mgra_to_mgrb.000001
Relay_Log_Pos:4
Relay_Source_Log_File:
Replica_IO_Running:No
Replica_SQL_Running:No
Replicate_Do_DB:

（3）模拟MGR B主节点故障

这里不能通过对MGR B执行切主命令模拟故障，会报如下错误：

mysql>selectgroup_replication_set_as_primary('3fa9e064-be4a-11ed-92c7-00163ea5c598');
ERROR3910(HY000):Thefunction'group_replication_set_as_primary'failed.Thereisaslavechannelrunninginthegroup'scurrentprimarymember.

我们通过停止组复制让MGR B主节点6005主动退出组，模拟故障

mysql>stopgroup_replication;
QueryOK,0rowsaffected(11.67sec)

（4）查看当前MGR B信息

mysql>select*fromperformance_schema.replication_group_members;
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|CHANNEL_NAME|MEMBER_ID|MEMBER_HOST|MEMBER_PORT|MEMBER_STATE|MEMBER_ROLE|MEMBER_VERSION|MEMBER_COMMUNICATION_STACK|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|group_replication_applier|3fa9e064-be4a-11ed-92c7-00163ea5c598|172.17.140.252|6006|ONLINE|PRIMARY|8.0.31|XCom|
|group_replication_applier|6a9691c6-be4a-11ed-8a32-00163ea5c598|172.17.140.252|6007|ONLINE|SECONDARY|8.0.31|XCom|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
2rowsinset(0.00sec)

当前MGR B发生切主，新主节点为6006

（5）查看异步复制信息

登录MGR B新主节点6006

mysql>showreplicastatusG
***************************1.row***************************
Replica_IO_State:Waitingforsourcetosendevent
Source_Host:172.17.140.201
Source_User:repl_user
Source_Port:6002
Connect_Retry:10
Source_Log_File:binlog.000001
Read_Source_Log_Pos:3343
Relay_Log_File:relaylog-mgra_to_mgrb.000002
Relay_Log_Pos:395
Relay_Source_Log_File:binlog.000001
Replica_IO_Running:Yes
Replica_SQL_Running:Yes
Replicate_Do_DB:

可以看到MGR B新主节点已经自动进行异步连接故障转移，与MGR A主节点6002建立连接并且连接正常，在此过程中并不需要人为去操作。

3.12 设置备集群MGR B为超级只读模式

配置MGR B集群所有节点为超级只读模式，避免执行误操作。默认情况下，MGR单主模式下主节点为读写模式，从节点为超级只读模式。

当一个组只是作为另一个组的备份的时候，只需要执行复制事物就可以了，不需要登录执行其他客户端事物，避免造成数据不一致的问题。因此我们可以通过 group_replication_disable_member_action() 函数设置成员操作，将备集群所有节点设置为超级只读模式，即使切主后选出新的主节点也要保持超级只读模式。

（1）查看MGR B当前成员操作

mysql>select*fromreplication_group_member_actions;
+------------------------------------------+------------------------+---------+----------+----------+----------------+
|name|event|enabled|type|priority|error_handling|
+------------------------------------------+------------------------+---------+----------+----------+----------------+
|mysql_disable_super_read_only_if_primary|AFTER_PRIMARY_ELECTION|1|INTERNAL|1|IGNORE|
|mysql_start_failover_channels_if_primary|AFTER_PRIMARY_ELECTION|1|INTERNAL|10|CRITICAL|
+------------------------------------------+------------------------+---------+----------+----------+----------------+
2rowsinset(0.02sec)

（2）设置MGR B为超级只读模式

mysql>SELECTgroup_replication_disable_member_action("mysql_disable_super_read_only_if_primary","AFTER_PRIMARY_ELECTION");
+---------------------------------------------------------------------------------------------------------------+
|group_replication_disable_member_action("mysql_disable_super_read_only_if_primary","AFTER_PRIMARY_ELECTION")|
+---------------------------------------------------------------------------------------------------------------+
|OK|
+---------------------------------------------------------------------------------------------------------------+
1rowinset(0.04sec)

注意：这里执行完此函数后，不会对当前主节点产生影响，当发生切主选择出新主节点后，会将新主节点设置为超级只读模式。

（3）停止MGR B主节点

mysql>stopgroup_replication;
QueryOK,0rowsaffected(28.54sec)

mysql>select*fromperformance_schema.replication_group_members;
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|CHANNEL_NAME|MEMBER_ID|MEMBER_HOST|MEMBER_PORT|MEMBER_STATE|MEMBER_ROLE|MEMBER_VERSION|MEMBER_COMMUNICATION_STACK|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
|group_replication_applier|190f4674-be4a-11ed-9452-00163ea5c598|172.17.140.252|6005|ONLINE|PRIMARY|8.0.31|XCom|
|group_replication_applier|6a9691c6-be4a-11ed-8a32-00163ea5c598|172.17.140.252|6007|ONLINE|SECONDARY|8.0.31|XCom|
+---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+----------------------------+
2rowsinset(0.01sec)

MGR B新主节点为 6005

（4）查看MGR B新主节点是否进入超级只读模式

mysql>showvariableslike'super_read_only';
+-----------------+-------+
|Variable_name|Value|
+-----------------+-------+
|super_read_only|ON|
+-----------------+-------+
1rowinset(0.05sec)

mysql>createdatabasett;
ERROR1290(HY000):TheMySQLserverisrunningwiththe--super-read-onlyoptionsoitcannotexecutethisstatement

此时新主节点处于超级只读模式，不允许用户执行操作。

4.总结

通过异步连接故障切换机制，当复制连接出现问题时，不需要人工介入手动去重新建立复制连接，副本会自动进行异步故障转移与新的节点建立连接。

异步复制通道的建立只能在2个MGR集群的主节点上。

审核编辑：刘清

MGR主备集群实现异步连接故障转移的步骤

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