### 18.2.2 Deploying Group Replication Locally

 The most common way to deploy Group Replication is using multiple server instances, to provide high availability. It is also possible to deploy Group Replication locally, for example for testing purposes. This section explains how you can deploy Group Replication locally.

Important

 Group Replication is usually deployed on multiple hosts because this ensures that high-availability is provided. The instructions in this section are not suitable for production deployments because all MySQL server instances are running on the same single host. In the event of failure of this host, the whole group fails. Therefore this information should be used for testing purposes and it should not be used in a production environments.

 This section explains how to create a replication group with three MySQL Server instances on one physical machine. This means that three data directories are needed, one per server instance, and that you need to configure each instance independently. This - procedure assumes that MySQL Server was downloaded and unpacked - into the directory named `mysql-8.0`. Each MySQL server instance requires a specific data directory. Create a directory named `data`, then in that directory create a subdirectory for each server instance, for example s1, s2 and s3, and initialize each one.

```
mysql-8.0/bin/mysqld --initialize-insecure --basedir=$PWD/mysql-8.0 --datadir=$PWD/data/s1
mysql-8.0/bin/mysqld --initialize-insecure --basedir=$PWD/mysql-8.0 --datadir=$PWD/data/s2
mysql-8.0/bin/mysqld --initialize-insecure --basedir=$PWD/mysql-8.0 --datadir=$PWD/data/s3
```

 Inside `data/s1`, `data/s2`, `data/s3` is an initialized data directory, containing the mysql system database and related tables and much more. To learn more about the initialization procedure, see [Section 2.10.1, “Initializing the Data Directory”](data-directory-initialization.html).

Warning

 Do not use `-initialize-insecure` in production environments, it is only used here to simplify the tutorial. For more information on security settings, see [Section 18.6, “Group Replication Security”](group-replication-security.html).

#### Configuration of Local Group Replication Members

 When you are following [Section 18.2.1.2, “Configuring an Instance for Group Replication”](group-replication-configuring-instances.html), you need to add configuration for the data directories added in the previous section. For example:

```
[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.

Note

 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 [`report_host=127.0.0.1`](replication-options-replica.html#sysvar_report_host).

 Then each member needs to be able to connect to the other members on their [`group_replication_local_address`](group-replication-options.html#sysvar_group_replication_local_address). For example in the option file of member s1 add:

```
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"
```

 This configures s1 to use port 24901 for internal group communication with seed members. For each server instance you want to add to the group, make these changes in the option file of the member. For each member you must ensure a unique address is specified, so use a unique port per instance for [`group_replication_local_address`](group-replication-options.html#sysvar_group_replication_local_address). Usually you want all members to be able to serve as seeds for members that are joining the group and have not got the transactions processed by the group. In this case, add all of the ports to [`group_replication_group_seeds`](group-replication-options.html#sysvar_group_replication_group_seeds) as shown above.

 The remaining steps of [Section 18.2.1, “Deploying Group Replication in Single-Primary Mode”](group-replication-deploying-in-single-primary-mode.html) apply equally to a group which you have deployed locally in this way.

