MariaDB DR Galera 3 node Replication

Which Linux is it, and what does your yum repo point at?

Here are the details :

[root@mncdf456 ~]# cat /etc/os-release
NAME="Red Hat Enterprise Linux Server"
VERSION="7.6 (Maipo)"
ID="rhel"
ID_LIKE="fedora"
VARIANT="Server"
VARIANT_ID="server"
VERSION_ID="7.6"
PRETTY_NAME="Red Hat Enterprise Linux Server 7.6 (Maipo)"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:redhat:enterprise_linux:7.6:GA:server"
HOME_URL="https://www.redhat.com/"
BUG_REPORT_URL="https://bugzilla.redhat.com/"

REDHAT_BUGZILLA_PRODUCT="Red Hat Enterprise Linux 7"
REDHAT_BUGZILLA_PRODUCT_VERSION=7.6
REDHAT_SUPPORT_PRODUCT="Red Hat Enterprise Linux"
REDHAT_SUPPORT_PRODUCT_VERSION="7.6"

[root@mncdf456 ~]# sudo yum install mariadb-plugin-connect
Loaded plugins: langpacks, product-id, search-disabled-repos, subscription-manager
rhel-7-server-extras-rpms | 3.4 kB 00:00:00
rhel-7-server-optional-rpms | 3.2 kB 00:00:00
rhel-7-server-rpms | 3.5 kB 00:00:00
(1/6): rhel-7-server-extras-rpms/x86_64/updateinfo | 218 kB 00:00:00
(2/6): rhel-7-server-optional-rpms/7Server/x86_64/updateinfo | 2.5 MB 00:00:01
(3/6): rhel-7-server-rpms/7Server/x86_64/updateinfo | 3.5 MB 00:00:01
(4/6): rhel-7-server-extras-rpms/x86_64/primary_db | 591 kB 00:00:01
(5/6): rhel-7-server-optional-rpms/7Server/x86_64/primary_db | 8.5 MB 00:00:02
(6/6): rhel-7-server-rpms/7Server/x86_64/primary_db | 67 MB 00:00:15
No package mariadb-plugin-connect available.
Error: Nothing to do

[root@mncdf456 ~]#
[root@mncdf456 ~]#
[root@mncdf456 ~]# yum info MariaDB-server
Loaded plugins: langpacks, product-id, search-disabled-repos, subscription-manager
Installed Packages
Name : MariaDB-server
Arch : x86_64
Version : 10.2.25
Release : 1.el7.centos
Size : 116 M
Repo : installed
Summary : MariaDB: a very fast and robust SQL database server
URL : http://mariadb.org
License : GPLv2
Description :
:
: It is GPL v2 licensed, which means you can use the it free of charge under the
: conditions of the GNU General Public License Version 2 (http://www.gnu.org/licenses/).
:
: MariaDB documentation can be found at https://mariadb.com/kb
: MariaDB bug reports should be submitted through https://jira.mariadb.org

Available Packages
Name : mariadb-server
Arch : x86_64
Epoch : 1
Version : 5.5.64
Release : 1.el7
Size : 11 M
Repo : rhel-7-server-rpms/7Server/x86_64
Summary : The MariaDB server and related files
URL : http://mariadb.org
License : GPLv2 with exceptions and LGPLv2 and BSD
Description : MariaDB is a multi-user, multi-threaded SQL database server. It is a
: client/server implementation consisting of a server daemon (mysqld)
: and many different client programs and libraries. This package contains
: the MariaDB server and some accompanying files and directories.
: MariaDB is a community developed branch of MySQL.

[root@mncdf456 ~]# cd /usr/lib64/mysql/plugin
[root@mncdf456 plugin]# ls -l ha_connect.so
ls: cannot access ha_connect.so: No such file or directory

[root@mncdf456 plugin]# ls -l ha*
-rwxr-xr-x 1 root root 95040 Jun 15 2019 ha_archive.so
-rwxr-xr-x 1 root root 66280 Jun 15 2019 ha_blackhole.so
-rwxr-xr-x 1 root root 91072 Jun 15 2019 ha_federated.so
-rwxr-xr-x 1 root root 123712 Jun 15 2019 ha_federatedx.so
-rwxr-xr-x 1 root root 6561072 Jun 15 2019 ha_mroonga.so
-rwxr-xr-x 1 root root 211016 Jun 15 2019 handlersocket.so
-rwxr-xr-x 1 root root 164848 Jun 15 2019 ha_sphinx.so
-rwxr-xr-x 1 root root 914184 Jun 15 2019 ha_spider.so
[root@mncdf456 plugin]#

I still don't see which repository you installed MariaDB-server from. I've checked several CentOS and RHEL repos, all of them have the package, but there are many of them, maybe you're using an unlucky one.

Also, the description and the comment seem to be from different hosts, with a lot of mix-up.

If you install MariaDB from the MariaDB repo, as you apparently did in the comment, then the correct package Connect name is the one that you used in the description,

sudo yum install MariaDB-connect-engine

But in the comment you are trying to use mariadb-plugin-connect instead, which indeed doesn't exist, at least not in MariaDB YUM repos.