Editing Training 2022 Linux team/ (section)

==Training session on Radico Client Training Video - Tetra Support Staff - Alok Singh==

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'''Video summary:''' "Radico Client Training Video" -- a hands-on MySQL master-slave replication architecture walkthrough for the Radico client, run over remote desktop rather than VPN since this client doesn't provide VPN access. Radico's application is a LAMP-style setup (a separate Apache server) with dedicated database servers split across two physical locations, Sitapur and Rampur -- each location runs one MySQL master and one MySQL slave (4 database servers total, 2 pairs). The presenter built the Sitapur pair personally (Rampur's was inherited/pre-existing but functionally identical) and documented the setup on the internal wiki. Explains the replication mechanics: MySQL Community Edition installed on both nodes; the master grants a dedicated replication user/password to the slave; key config values on the master include `server-id` and `gtid_mode`, and GTID (Global Transaction ID) is the mechanism used to verify replication is actually in sync -- checked via `SHOW SLAVE STATUS` on the slave and comparing its GTID reference against the master's `SHOW MASTER STATUS` / executed-GTID-set output, which must match. Config changes (e.g. raising `max_connections` from a default like 500) go in `my.cnf` under the `[mysqld]` section, requiring a MySQL restart to take effect. Explains the operational significance of master-slave (as opposed to master-master, contrasted with the YouSecure architecture covered elsewhere on this wiki): failover here is NOT automatic -- the application server only ever points at the master's IP, so if the master goes down, promoting the slave requires manually and completely shutting down the dead master first, then reassigning its IP to the slave, since the application has no built-in awareness of the slave's existence; this must never be done to a live/running master, only after confirming it's fully down, since two servers simultaneously claiming the master IP would cause serious problems. Contrasts this with a master-master setup (like YouSecure) where both nodes replicate bidirectionally and either can serve as primary behind a load balancer, with automatic failover. Closes confirming Radico's total footprint is 4 database servers (2 master-slave pairs, one per location), with a light aside about the recording being on.