Make mysql replicas to work with MySQL 5.7 and 5.8

This fixes moodlehq#80. It has been detected that MySQL main/replica
configurations have stopped working. My personal bet is that
some changes in the MySQL images have leaded to that, or maybe
they were working for MySQL 5.6 and never have worked to 5.7.

NVM, this commit just makes them back to work for both 5.7 and 8.0,
that are the currently "supported" MySQL databases.

Note that, after this PR, we'll be checking the MariaDB main/replica
configurations because they may need similar changes.

Also, while I've tested the solution locally, we are lacking any own
CI for this product, so I've created an issue about that:

moodlehq#81

Finally, here there are the explanations about the changes performed:

1. Moved the bin logs from /var/log/mysql to /var/lib/mysql . Reason
   being that the former directory doesn't exist anymore in MySQL 5.7
   and up (and also, that the binary logs are better with data than
   with logs).
2. Removed the 'multi_admin' user related stuff. Not needed at all.
3. Minor changes to moodle and root GRANT/IDENTIFIED stuff because
   of changes in MySQL 8 (already deprecated in 5.7). Use ALTER USER
   instead.
4. Use IDENTIFIED WITH mysql_native_password (the old password schema),
   because MySQL 8, when using the new hashed schema requires
   communications between the hosts to be encrypted. We don't need that
   extra complexity and while it can be disabled as part of the CHANGE MASTER TO
   command... it cannot be disabled for MySQL 5.7. SO the only option
   working in both versions is the used one (force old passwords schema
   for the replication user).
5. Remove the need of stopping and starting the temp server in the
   replica. All the commands can be executed with the temp server
   running and then the container entrypoint manageing itself will stop
   the temp server and start the final one.
6. Stop needing gosu completely. Now the replica conf files are made
   available via volume mount (like the standalone or main cases).

And that's all. The changes are small and subtle, but each one is
for a good reason, I think.

runner/master/mysql.d/master/conf.d/master.cnf

@@ -16,7 +16,7 @@ read_buffer_size = 1M
 innodb_flush_log_at_trx_commit  = 1
 
 server-id = 1
-log_bin                     = /var/log/mysql/mysql-bin.log
+log_bin                     = /var/lib/mysql/mysql-bin.log
 sync_binlog                 = 1
 binlog-format               = ROW
 

runner/master/mysql.d/master/docker-entrypoint-initdb.d/01_privileges.sql

@@ -1,8 +1,6 @@
-GRANT SHUTDOWN ON *.* TO 'multi_admin'@'localhost' IDENTIFIED BY 'multipass';
-CREATE USER 'replication'@'%' IDENTIFIED BY 'replication';
+CREATE USER 'replication'@'%' IDENTIFIED WITH mysql_native_password BY 'replication';
 GRANT REPLICATION SLAVE ON *.* TO 'replication'@'%';
 
-GRANT ALL ON *.* TO 'root'@'%' IDENTIFIED BY 'moodle';
-GRANT ALL ON *.* TO 'moodle'@'%' IDENTIFIED BY 'moodle';
+ALTER USER 'root'@'%' IDENTIFIED BY 'moodle';
 
 FLUSH PRIVILEGES;

runner/master/mysql.d/slave/conf.d/slave.cnf

@@ -0,0 +1,7 @@
+[mysqld]
+server-id = 2
+relay-log = /var/lib/mysql/mysql-relay-bin.log
+log_bin = /var/lib/mysql/mysql-bin.log
+
+# List of databases to replicate.
+binlog_do_db = moodle

runner/master/mysql.d/slave/docker-entrypoint-initdb.d/10_replicate.sh

@@ -7,18 +7,6 @@ echo "==========================================================================
 
 sleep 5
 
-# We need to set this for some inane reason otherwise it fails to start mysql.
-# This seems to be a bug with the entrypoint.sh
-DATABASE_ALREADY_EXISTS='true'
-
-docker_temp_server_stop
-
-echo "Copying moodle.cnf"
-gosu root cp /config/moodle.cnf /etc/mysql/conf.d/
-
-echo "Restarting mysqld"
-docker_temp_server_start mysqld
-
 echo "Dumping ${DBHOST}"
 mysql -u root -pmoodle -h ${DBHOST} -e "FLUSH TABLES WITH READ LOCK;" moodle
 mysql -u root -pmoodle -h ${DBHOST} -e "SHOW MASTER STATUS;" moodle
@@ -38,14 +26,6 @@ echo "Current position is {$replfile} {$position}"
 echo "Restoring into client"
 mysql -u root -pmoodle moodle < /tmp/moodle.sql
 
-echo "Stopping server to apply slave configuration"
-docker_temp_server_stop
-gosu root cp /config/slave.cnf /etc/mysql/conf.d/
-
-echo "Restarting mysqld"
-docker_temp_server_start mysqld
-
-echo "Starting slave"
 mysql -u root -pmoodle moodle << EOSQL
 CHANGE MASTER TO
   MASTER_HOST='${DBHOST}',

runner/master/run.sh

@@ -335,14 +335,10 @@ then
       -e MYSQL_PASSWORD="${DBPASS}" \
       -e DBHOST=$DBHOST \
       -e DBHOST_SLAVE=$DBHOST_SLAVE \
-      -v $SCRIPTPATH/mysql.d/slave/config:/config \
+      -v $SCRIPTPATH/mysql.d/slave/conf.d:/etc/mysql/conf.d \
       -v $SCRIPTPATH/mysql.d/slave/docker-entrypoint-initdb.d:/docker-entrypoint-initdb.d \
       --tmpfs /var/lib/mysql:rw \
       mysql:${DBTAG}
-
-    # Hack to make gosu work for all users on the slave.
-    docker exec -u root $DBHOST_SLAVE bash -c 'chown root:mysql /usr/local/bin/gosu'
-    docker exec -u root $DBHOST_SLAVE bash -c 'chmod +s /usr/local/bin/gosu'
   else
     echo "Starting standalone"
     docker run \
@@ -395,7 +391,7 @@ then
       -e MYSQL_PASSWORD="${DBPASS}" \
       -e DBHOST=$DBHOST \
       -e DBHOST_SLAVE=$DBHOST_SLAVE \
-      -v $SCRIPTPATH/mysql.d/slave/config:/config \
+      -v $SCRIPTPATH/mysql.d/slave/conf.d:/etc/mysql/conf.d \
       -v $SCRIPTPATH/mysql.d/slave/docker-entrypoint-initdb.d:/docker-entrypoint-initdb.d \
       --tmpfs /var/lib/mysql:rw \
       mariadb:${DBTAG}