Deploying 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” . 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” . Warning Configuration of Local Group Replication Members When you are following Section 18.2.1.2, “Configuring an Instance for Group Replication” , 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. 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 . 3715 Note