What are the consequences of updating the application version directly in a replicated database?

Updating the application version directly in the replicated database can lead to several serious consequences:

1. Data inconsistency — if the new application version uses a different database schema or changes data handling logic, it can cause desynchronization between the master and replica nodes.

2. Replication issues — changes in table structures or data can cause replication errors, halt the process, or lead to data loss.

3. Application malfunction — if the replica is used for reading and the new application version is incompatible with the current state of the replica, it can result in errors and failures.

4. Performance loss — updates during replication can cause locks, slowdowns, and degrade system responsiveness.

5. Rollback difficulties — if the update is performed incorrectly, rollback can be complicated due to desynchronization between replicas.

Therefore, updating the application and database in a replicated environment is usually done using strategies such as:

• Updating first on the master node with compatibility checks.
• Gradual update of replicas.
• Using database migrations with backward compatibility.
• Testing updates in a staging environment that simulates replication.

Failure to follow these measures can result in serious failures and data loss.