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MySQL topology

MySQL runs on both nodes of the databases cluster:
  • cluster-n03 – treated operationally as the primary MySQL node.
  • cluster-n04 – treated operationally as the backup / replica MySQL node.
Exact replication status (master vs slave, GTID, etc.) cannot be queried without proper MySQL credentials, but from the services’ perspective both hosts run MySQL 5.7 and are configured as part of the same topology.

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MySQL on cluster-n03

  • Version: mysql Ver 14.14 Distrib 5.7.33, for Linux (x86_64)
  • Service: mysql.service (enabled, active)
  • Unit file: /lib/systemd/system/mysql.service
  • Data / config:
    • Uses the standard Debian/Ubuntu layout.
    • Exact datadir and replication settings require MySQL access.
Useful commands: 
ssh cluster-n03
systemctl status mysql
mysql --version
Notes:
  • Access for the yazan user without a password is not permitted (ERROR 1045), so DBAs should use appropriate MySQL users/credentials.
  • Operationally, this node is considered the main write node for MySQL workloads.

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MySQL on cluster-n04

  • Version: mysql Ver 14.14 Distrib 5.7.36, for Linux (x86_64)
  • Service: mysql.service (enabled, active)
  • Unit file: /lib/systemd/system/mysql.service
Useful commands: 
ssh cluster-n04
systemctl status mysql
mysql --version
Notes:
  • Similar to cluster-n03, we cannot read replication status without DB credentials.
  • Treated as the backup / replica node in case of issues with cluster-n03.

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Operational hints

  • To confirm roles and replication, DBAs should run: 
    SHOW SLAVE STATUS\G
SHOW MASTER STATUS\G
SELECT @@hostname, @@server_id, @@global.read_only;
  • Application endpoints and failover logic for MySQL should be documented in the relevant application or infrastructure modules (load balancers, DNS, etc.).

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Cron jobs & backups

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cluster-n03

  • No custom root crontab configured for MySQL or other database tasks.
  • Only standard system cron jobs under /etc/cron.* (e.g. logrotate, mdadm, fstrim, etc.).

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cluster-n04

  • Root crontab includes a MySQL backup job: 
    5 3,9,15,21 * * * bash -c "/root/mysql.backup.sh"
    • Runs at 03:05, 09:05, 15:05, and 21:05 every day.
    • Executes /root/mysql.backup.sh as root (exact backup behavior is defined in that script).
System cron directories on cluster-n04 otherwise contain only standard OS maintenance jobs.