Database
Domain 5 covers NHN Cloud managed databases: RDS for MySQL, MariaDB, and PostgreSQL, plus Cloud DB for Redis. The exam tests managed-service boundaries: what the platform handles and what you still must configure.
Core rules
- RDS provisions a database instance in a VPC subnet. You choose engine version, flavor, storage, subnet, and security group. The DB endpoint is private unless you deliberately expose it.
- The platform handles installation, patching options, backups, and monitoring. You still own schema design, indexes, query tuning, accounts, and parameter values that affect behavior.
- Backups use retention settings and restore creates a new DB instance; restoring does not overwrite the original. Test restore time as part of recovery design.
- High availability uses a standby or failover configuration where supported. A failover changes the primary endpoint behavior; applications must reconnect.
- Redis is an in-memory cache, not a primary relational store. Use it for sessions, counters, and hot data with an expiry policy.
Worked example
A read-heavy web app uses RDS for MySQL. Create a primary in a private subnet, set automated backups to 7 days, and add a read replica for reporting queries. Point the web tier at the primary endpoint and reports at the replica endpoint. Reason: writes go to the primary; reports avoid competing with transactions; backups provide a restore point. Do not send writes to a read replica.
Traps
Do not open the DB security group to 0.0.0.0/0. Do not assume a backup restores in place. Do not use Redis as durable system of record. Do not ignore storage autoscaling and connection limits.