This section explains the configuration settings required for MySQL Server instances that you want to use for Group Replication. For background information, see Section 18.9.2, “Group Replication Limitations”.
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 220.127.116.11, “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.
[mysqld] # server configuration datadir=<full_path_to_data>/data/s1 basedir=<full_path_to_bin>/mysql-8.0/ port=24801 socket=<full_path_to_sock_dir>/s1.sock
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.
Group Replication requires a network connection between the
members, which means that each member must be able to resolve
the network address of all of the other members. For example
in this tutorial all three instances run on one machine, so to
ensure that the members can contact each other you could add a
line to the option file such as
For Group Replication, data must be stored in the InnoDB
transactional storage engine (for details of why, see
Section 18.9.1, “Group Replication Requirements”). The use of
other storage engines, including the temporary
MEMORY storage engine, might
cause errors in Group Replication. Set the
system variable as follows to prevent their use:
Note that with the
engine disabled, when you are upgrading a MySQL instance to a
release where mysql_upgrade is still used
(before MySQL 8.0.16), mysql_upgrade might
fail with an error. To handle this, you can re-enable that
storage engine while you run mysql_upgrade,
then disable it again when you restart the server. For more
information, see Section 4.4.5, “mysql_upgrade — Check and Upgrade MySQL Tables”.
The following settings configure replication according to the MySQL Group Replication requirements.
server_id=1 gtid_mode=ON enforce_gtid_consistency=ON binlog_checksum=NONE
These settings configure the server to use the unique identifier number 1, to enable global transaction identifiers, to allow execution of only statements that can be safely logged using a GTID, and to disable writing checksums for events written to the binary log.
If you are using a version of MySQL earlier than 8.0.3, where the defaults were improved for replication, you need to add these lines to the member's option file.
log_bin=binlog log_slave_updates=ON binlog_format=ROW master_info_repository=TABLE relay_log_info_repository=TABLE
These settings instruct the server to turn on binary logging, use row-based format, to store replication metadata in system tables instead of files and disable binary log event checksums. For more details see Section 18.9.1, “Group Replication Requirements”.
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.
transaction_write_set_extraction=XXHASH64 group_replication_group_name="aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa" group_replication_start_on_boot=off group_replication_local_address= "127.0.0.1:24901" group_replication_group_seeds= "127.0.0.1:24901,127.0.0.1:24902,127.0.0.1:24903" group_replication_bootstrap_group=off
transaction_write_set_extractioninstructs the server that for each transaction it has to collect the write set and encode it as a hash using the XXHASH64 hashing algorithm. From MySQL 8.0.2, this setting is the default, so this line can be omitted.
group_replication_group_nametells the plugin that the group that it is joining, or creating, is named "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa".
The value of
group_replication_group_namemust be a valid UUID. This UUID is used internally when setting GTIDs for Group Replication events in the binary log. Use
SELECT UUID()to generate a UUID.
group_replication_start_on_bootinstructs 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_bootto on so that Group Replication starts automatically upon server boot.
group_replication_local_addresstells the plugin to use the network address 127.0.0.1 and port 24901 for internal communication with other members in the group.Important
Group Replication uses this address for internal member-to-member connections involving remote instances of the group communication engine (XCom, a Paxos variant). This address must be different to the hostname and port used for SQL and it must not be used for client applications. It must be reserved for internal communication between the members of the group while running Group Replication.
The network address configured by
group_replication_local_addressmust 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/hostsfiles, 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 18.4.6, “Support For IPv6 And For Mixed IPv6 And IPv4 Groups”.
The recommended port for
group_replication_local_addressis 33061. In this tutorial we use three server instances running on one machine, thus ports 24901 to 24903 are used for the internal communication network address.
group_replication_local_addressis 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, and as demonstrated in this tutorial, you can use the same host name or IP address for all members as long as the ports are all different.
group_replication_group_seedssets 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_seedslist contains the
hostname:portof 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.Important
group_replication_group_seedsis the seed member's internal network address, configured by
group_replication_local_addressand not the SQL
hostname:portused for client connections, and shown for example in
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.Warning
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 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.
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_seedsoption. 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_addressif 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, “IP Address Whitelisting”.
group_replication_bootstrap_groupinstructs the plugin whether to bootstrap the group or not.Important
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
This is illustrated later in this tutorial.