18.2.1.2 Configuring an Instance for Group Replication

plugin-load-add adds the Group Replication plugin to the list of plugins which the server loads at startup. This is preferable in a production deployment to installing the plugin manually.

Configuring group_replication_group_name tells the plugin that the group that it is joining, or creating, is named "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa".

The value of group_replication_group_name must be a valid UUID. This UUID is used internally when setting GTIDs for Group Replication events in the binary log. You can use SELECT UUID() to generate a UUID.

Configuring the group_replication_start_on_boot variable to off instructs the plugin to not start operations automatically when the server starts. This is important when setting up Group Replication as it ensures you can configure the server before manually starting the plugin. Once the member is configured you can set group_replication_start_on_boot to on so that Group Replication starts automatically upon server boot.

Configuring group_replication_local_address sets the network address and port which the member uses for internal communication with other members in the group. Group Replication uses this address for internal member-to-member connections involving remote instances of the group communication engine (XCom, a Paxos variant).

The network address configured by group_replication_local_address must be resolvable by all group members. For example, if each server instance is on a different machine with a fixed network address, you could use the IP address of the machine, such as 10.0.0.1. If you use a host name, you must use a fully qualified name, and ensure it is resolvable through DNS, correctly configured /etc/hosts files, or other name resolution processes. From MySQL 8.0.14, IPv6 addresses (or host names that resolve to them) can be used as well as IPv4 addresses. A group can contain a mix of members using IPv6 and members using IPv4. For more information on Group Replication support for IPv6 networks and on mixed IPv4 and IPv6 groups, see Section 18.4.5, “Support For IPv6 And For Mixed IPv6 And IPv4 Groups”.

The recommended port for group_replication_local_address is 33061. group_replication_local_address is used by Group Replication as the unique identifier for a group member within the replication group. You can use the same port for all members of a replication group as long as the host names or IP addresses are all different, as demonstrated in this tutorial. Alternatively you can use the same host name or IP address for all members as long as the ports are all different, for example as shown in Section 18.2.2, “Deploying Group Replication Locally”.

Configuring group_replication_group_seeds sets the hostname and port of the group members which are used by the new member to establish its connection to the group. These members are called the seed members. Once the connection is established, the group membership information is listed at performance_schema.replication_group_members. Usually the group_replication_group_seeds list contains the hostname:port of each of the group member's group_replication_local_address, but this is not obligatory and a subset of the group members can be chosen as seeds.

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. In other words, any existing data which is on the server bootstrapping the group is what is used as the data for the next joining member. The second server joining asks the one and only member in the group to join, any missing data on the second server is replicated from the donor data on the bootstrapping member, and then the group expands. The third server joining can ask any of these two to join, data is synchronized to the new member, and then the group expands again. Subsequent servers repeat this procedure when joining.

A joining member must communicate with a seed member using the same protocol (IPv4 or IPv6) that the seed member advertises in the group_replication_group_seeds option. For the purpose of IP address whitelisting for Group Replication, the whitelist on the seed member must include an IP address for the joining member for the protocol offered by the seed member, or a host name that resolves to an address for that protocol. This address or host name must be set up and whitelisted in addition to the joining member's group_replication_local_address if the protocol for that address does not match the seed member's advertised protocol. If a joining member does not have a whitelisted address for the appropriate protocol, its connection attempt is refused. For more information, see Section 18.5.1, “Group Replication IP Address Whitelisting”.

Configuring group_replication_bootstrap_group instructs the plugin whether to bootstrap the group or not. In this case, even though s1 is the first member of the group we set this variable to off in the option file. Instead we configure group_replication_bootstrap_group when the instance is running, to ensure that only one member actually bootstraps the group.