06 — RDS & Databases

What is RDS?

Relational Database Service — managed SQL databases. AWS handles patching, backups, replication.

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

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RDS vs Self-Managed

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Creating an RDS Instance

aws rds create-db-instance \
  --db-instance-identifier my-db \
  --db-instance-class db.t3.micro \
  --engine postgres \
  --engine-version 16.1 \
  --master-username admin \
  --master-user-password supersecret \
  --allocated-storage 20 \
  --storage-type gp3 \
  --vpc-security-group-ids sg-xxx \
  --db-subnet-group-name my-db-subnet-group \
  --multi-az \
  --backup-retention-period 7 \
  --storage-encrypted

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Multi-AZ (High Availability)

Primary (AZ-a)  ──synchronous replication──→  Standby (AZ-b)
     ↑                                            ↑
  Reads/Writes                              Auto-failover
  (DNS endpoint)                            (promoted if primary fails)

Failover: ~60-120 seconds, same DNS endpoint

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Read Replicas (Scalability)

Primary ──async replication──→ Read Replica 1 (same region)
                           ──→ Read Replica 2 (cross-region)

Use cases:
  - Offload read-heavy queries (analytics, reporting)
  - Cross-region reads (lower latency)
  - Can be promoted to standalone DB (disaster recovery)

// Application code — separate read and write connections
const writePool = new Pool({ host: 'my-db.xxx.us-east-1.rds.amazonaws.com' });
const readPool = new Pool({ host: 'my-db-replica.xxx.us-east-1.rds.amazonaws.com' });

// Writes → primary
await writePool.query('INSERT INTO orders ...');

// Reads → replica
const result = await readPool.query('SELECT * FROM orders WHERE ...');

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Aurora

AWS's cloud-native relational DB. Compatible with PostgreSQL and MySQL.

Aurora Serverless v2:
  - Auto-scales compute (0.5 to 128 ACUs)
  - Pay per second of usage
  - Great for variable/unpredictable workloads

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Backups & Snapshots

# Automated backups (enabled by default)
# - Daily snapshot + transaction logs
# - Point-in-time restore (up to 35-day retention)

# Manual snapshot (persists after RDS deletion)
aws rds create-db-snapshot \
  --db-instance-identifier my-db \
  --db-snapshot-identifier my-db-backup-2024

# Restore from snapshot (creates new instance)
aws rds restore-db-instance-from-db-snapshot \
  --db-instance-identifier my-db-restored \
  --db-snapshot-identifier my-db-backup-2024

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Security

✅ Deploy in private subnet (no public access)
✅ Security group: allow port 5432 only from app layer SG
✅ Enable encryption at rest (KMS)
✅ Enable encryption in transit (SSL/TLS)
✅ Use IAM authentication or Secrets Manager for credentials
✅ Enable Enhanced Monitoring + Performance Insights

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Key Takeaways

• RDS = managed SQL database — AWS handles backups, patching, HA
• Multi-AZ for high availability (synchronous replication, auto-failover)
• Read Replicas for read scalability (async replication, up to 5)
• Aurora for best performance — 3-5x faster, auto-scaling storage, faster failover
• Aurora Serverless v2 for variable workloads — pay per second
• Always deploy in private subnets with encryption enabled