Practice Questions

RDS (Relational Database Service)

RDS is a managed relational database service that handles provisioning, patching, backups, and replication. You choose the database engine; AWS manages the infrastructure.

Supported engines: MySQL, PostgreSQL, MariaDB, Oracle, SQL Server, and Amazon Aurora.

Multi-AZ Deployments

Multi-AZ creates a synchronous standby replica in a different Availability Zone. Its sole purpose is high availability and automatic failover — not performance.

• Replication is synchronous — the primary waits for the standby to confirm writes before acknowledging the transaction
• The standby is not readable — it exists only for failover
• Failover is automatic (typically 1–2 minutes) and triggered by primary failure, AZ outage, or manual reboot with failover
• DNS endpoint does not change — applications automatically point to the new primary after failover
• Multi-AZ is for HA/failover, not read scaling

Read Replicas

Read replicas are asynchronous copies of the primary database used to offload read traffic and improve performance.

• Replication is asynchronous — slight lag is possible; replicas may be slightly behind
• Replicas are readable — applications can point read queries at them
• Up to 5 read replicas per RDS instance (15 for Aurora)
• Can be in the same AZ, different AZ, or different region (cross-region read replicas)
• Can be promoted to a standalone database (breaks replication)
• Read replicas do not provide automatic failover — use Multi-AZ for that

Multi-AZ vs. Read Replicas — the most tested comparison: