What is RDS?
Relational Database Service — a managed database service for SQL-based databases in the cloud.
Supported Engines
| Engine | Notes |
|---|---|
| PostgreSQL | Open source |
| MySQL | Open source |
| MariaDB | Open source |
| Oracle | Commercial |
| Microsoft SQL Server | Commercial |
| IBM DB2 | Commercial |
| Aurora | AWS proprietary (covered separately) |
Remember all 7 engine types supported by RDS.
Why RDS over DB on EC2?
RDS is a managed service. AWS handles:
| Feature | Description |
|---|---|
| Automated provisioning | DB + OS setup |
| OS patching | Automatic |
| Continuous backups | Point-in-Time Restore (up to 5 min ago) |
| Monitoring dashboards | Built-in performance metrics |
| Read Replicas | Up to 15, for read scaling |
| Multi AZ | Disaster recovery |
| Maintenance windows | Scheduled upgrades |
| Vertical scaling | Change instance type |
| Horizontal scaling | Add read replicas |
| Storage | Backed by EBS (gp2 or io1) |
You cannot SSH into RDS instances. It's a managed service — no access to the underlying EC2 instance. (Exception: RDS Custom)
RDS Storage Auto Scaling
┌──────────────┐ Threshold met? ┌──────────────────┐
│ RDS DB │ ──────────────────────▶ │ Auto-increase │
│ 20 GB used │ Free < 10% │ storage │
│ │ Low > 5 min │ (up to max) │
│ │ 6 hrs since last mod │ │
└──────────────┘ └──────────────────┘
| Setting | Detail |
|---|---|
| Trigger | Free storage < 10% of allocated |
| Duration | Low storage lasts > 5 minutes |
| Cooldown | 6 hours since last modification |
| Max threshold | You set the maximum storage limit |
| Supports | All RDS database engines |
Great for applications with unpredictable workloads. Avoids manual storage scaling operations.
Storage auto scaling triggers
Questions & Answers
Q1: What does RDS stand for and what is it?
Answer:
Relational Database Service. A managed AWS service for SQL databases in the cloud. AWS handles provisioning, patching, backups, monitoring, and scaling.
Q2: What are the 7 database engines supported by RDS?
Answer:
- PostgreSQL
- MySQL
- MariaDB
- Oracle
- Microsoft SQL Server
- IBM DB2
- Aurora (AWS proprietary)
Q3: Can you SSH into an RDS instance?
Answer:
No. RDS is a managed service — no access to the underlying EC2 instance. The only exception is RDS Custom (for Oracle and MS SQL Server).
Q4: What is Point-in-Time Restore?
Answer:
RDS continuously backs up transaction logs. You can restore your database to any point in time within the backup retention period (up to 5 minutes ago).
Q5: What storage type does RDS use?
Answer:
EBS volumes (gp2 for general purpose or io1 for provisioned IOPS).
Q6: When does RDS Storage Auto Scaling trigger?
Answer:
Three conditions must be met:
- Free storage < 10% of allocated
- Low storage persists for > 5 minutes
- 6 hours have passed since last storage modification
Q7: What is the benefit of RDS over deploying a DB on EC2?
Answer:
RDS provides automated provisioning, OS patching, backups, monitoring, read replicas, Multi AZ, maintenance windows, and scaling — all managed by AWS.
Q8: Can RDS scale both vertically and horizontally?
Answer:
Yes.
- Vertical: Change the instance type (e.g., db.t3.micro → db.r5.large)
- Horizontal: Add read replicas (up to 15)
Q9: Do you need to set a maximum storage threshold for auto scaling?
Answer:
Yes. You must set a maximum storage threshold to prevent unlimited growth.
Q10: Is RDS Storage Auto Scaling supported for all engines?
Answer:
Yes. It supports all RDS database engines (PostgreSQL, MySQL, MariaDB, Oracle, MS SQL Server, IBM DB2).
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