Configuring multiple instances of mysqld on almalinux - mysql

Question

I've been trying to setup multiple instances of mysqld on an almalinux box.
I can't get the systemctl start mysqld#replica03 statements to recognize the associated options setup in the /etc/my.cnf file.
If I change the [mysqld#replica03] or [mysqld#replica04] to [mysqld] it works and uses the appropriate datadir and port. As soon as I use [mysqld#replica03] and [mysqld#replica04] in the /etc/my.cnf file it uses the default /var/lib/msyql datadir and options instead of the ones I specified
I have run
systemctl enable mysqld#replica03
systemctl enable mysqld#replica04
Any ideas would be appreciated.
/etc/my.cnf file:
[client-server]
[mysqld#replica03]
server_id=3
port=3306
datadir=/var/lib/mysql_replica03
socket=/var/lib/mysql_replica03/mysql.sock
log-error=/var/log/mysql_replica03/mysqld.log
pid-file=/var/run/mysqld_replica03/mysqld.pid
[mysqld#replica04]
server_id=4
port=3307
datadir=/var/lib/mysql_replica04
socket=/var/lib/mysql_replica04/mysql.sock
log-error=/var/log/mysql_replica04/mysqld.log
pid-file=/var/run/mysqld_replica04/mysqld.pid

Answer 1

When you need multiple instances, and you're using systemd to achieve it, the server option groups configuration is the way to go.
The comment you made on your question shows that the suffix used is prefixed with a dot.
ExecStart=/usr/libexec/mysqld --defaults-group-suffix=.%I
So the server groups should be rewritten to
[mysqld.replica03]
server_id=3
port=3306
datadir=/var/lib/mysql_replica03
socket=/var/lib/mysql_replica03/mysql.sock
log-error=/var/log/mysql_replica03/mysqld.log
pid-file=/var/run/mysqld_replica03/mysqld.pid
[mysqld.replica04]
server_id=4
port=3307
datadir=/var/lib/mysql_replica04
socket=/var/lib/mysql_replica04/mysql.sock
log-error=/var/log/mysql_replica04/mysqld.log
pid-file=/var/run/mysqld_replica04/mysqld.pid
Another important observation is that the order in configuration files matters. Theses replica servers definitions need to be parsed after main [mysql] section.
my_print_defaults will help you with it:
$ my_print_defaults --defaults-group-suffix=.another mysqld
--datadir=/var/lib/mysql
--socket=/var/lib/mysql/mysql.sock
--log-error=/var/log/mariadb/mariadb.log
--pid-file=/run/mariadb/mariadb.pid
--datadir=/db/another/mysql
--socket=/db/another/mysql/mysql.sock
--log-error=/db/another/log/mariadb/mariadb.log
--pid-file=/run/mariadb/mariadb-another.pid
$
If your OS has a /etc/my.cnf.d/ directory, as mine does, you will need to sort the filenames in order to accommodate this requirement.
As I'm using mariadb, and I have a /etc/my.cnf.d/mariadb-server.cnf, my another server group is on a file named zz-another.cnf, making sure it will be parsed after mariadb-server.cnf.