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MySQL 5.7 Reference Manual  /  ...  /  Configuring an Instance for Group Replication Configuring an Instance for Group Replication

This section explains the configuration settings required for MySQL Server instances that you want to use for Group Replication. For background information, see Section 17.7.2, “Group Replication Limitations”.

Group Replication Server Settings

To install and use the Group Replication plugin you must configure the MySQL Server instance correctly. It is recommended to store the configuration in the instance's configuration file. See Section 4.2.6, “Using Option Files” for more information. Unless stated otherwise, what follows is the configuration for the first instance in the group, referred to as s1 in this procedure. The following section shows an example server configuration.


# server configuration


These settings configure MySQL server to use the data directory created earlier and which port the server should open and start listening for incoming connections.


The non-default port of 24801 is used because in this tutorial the three server instances use the same hostname. In a setup with three different machines this would not be required.

Replication Framework

The following settings configure replication according to the MySQL Group Replication requirements.


These settings configure the server to use the unique identifier number 1, to enable global transaction identifiers and to store replication metadata in system tables instead of files. Additionally, it instructs the server to turn on binary logging, use row-based format and disable binary log event checksums. For more details see Section 17.7.2, “Group Replication Limitations”.

Group Replication Settings

At this point the my.cnf file ensures that the server is configured and is instructed to instantiate the replication infrastructure under a given configuration. The following section configures the Group Replication settings for the server.

loose-group_replication_local_address= ""
loose-group_replication_group_seeds= ",,"
loose-group_replication_bootstrap_group= off

The loose- prefix used for the group_replication variables above instructs the server to continue to start if the Group Replication plugin has not been loaded at the time the server is started.

  • Line 1 instructs the server that for each transaction it has to collect the write set and encode it as a hash using the XXHASH64 hashing algorithm.

  • Line 2 tells the plugin that the group that it is joining, or creating, is named "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa".

  • Line 3 instructs the plugin to not start operations automatically when the server starts.

  • Line 4 tells the plugin to use the IP address, or localhost, and port 24901 for incoming connections from other members in the group.


    The server listens on this port for member-to-member connections. This port must not be used for user applications at all, it must be reserved for communication between different members of the group while running Group Replication.

    The local address configured by group_replication_local_address must be accessible to all group members. For example, if each server instance is on a different machine use the IP and port of the machine, such as The recommended port for group_replication_local_address is 33061, but in this tutorial we use three server instances running on one machine, thus ports 24901 to 24903 are used.

  • Line 5 tells the plugin that the following members on those hosts and ports should be contacted in case it needs to join the group. These are seed members, which are used when this member wants to connect to the group. Upon joining the server contacts one of them first (seed) and then it asks the group to reconfigure to allow the joining server to be accepted in the group. Note that this option does not need to list all members in the group, but rather a list of servers that should be contacted in case this server wishes to join the group.

    The server that starts the group does not make use of this option, since it is the initial server and as such, it is in charge of bootstrapping the group. The second server joining asks the one and only member in the group to join and then the group expands. The third server joining can ask any of these two to join, and then the group expands again. Subsequent servers repeat this procedure when joining.


    When joining multiple servers at the same time, make sure that they point to seed members that are already in the group. Do not use members that are also joining the group as as seeds, because they may not yet be in the group when contacted.

    It is good practice to start the bootstrap member first, and let it create the group. Then make it the seed member for the rest of the members that are joining. This ensures that there is a group formed when joining the rest of the members.

    Creating a group and joining multiple members at the same time is not supported. It may work, but chances are that the operations race and then the act of joining the group ends up in an error or a time out.

  • Line 6 instructs the plugin whether to boostrap the group or not.


    This option must only be used on one server instance at any time, usually the first time you bootstrap the group (or in case the entire group is brought down and back up again). If you bootstrap the group multiple times, for example when multiple server instances have this option set, then they could create an artificial split brain scenario, in which two distinct groups with the same name exist. Disable this option after the first server instance comes online.

Configuration for all servers in the group is quite similar. You need to change the specifics about each server (for example server_id, datadir, group_replication_local_address). This is illustrated later in this tutorial.

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