Answer: Buy reserved DB instances for the total workload. Make the Amazon RDS for PostgreSQL DB instance larger.

## Explanation **Correct Answer: A** **Why Option A is correct:** 1. **Vertical scaling (making the DB instance larger)** is the most cost-effective way to handle increased workload without adding infrastructure. By upgrading to a larger instance type (more CPU, memory, and I/O capacity), you can accommodate higher loads. 2. **Buying reserved instances** provides significant cost savings (up to 72% compared to on-demand pricing) for predictable workloads. 3. This approach avoids the complexity and additional costs of managing multiple DB instances while providing immediate capacity increase. **Why other options are incorrect:** **Option B (Multi-AZ DB instance):** - Multi-AZ deployment provides high availability and disaster recovery by maintaining a standby replica in another Availability Zone. - While it improves resilience, it doesn't directly address performance scaling and actually increases costs by requiring a standby instance. **Option C (Add another DB instance):** - Adding another DB instance means horizontal scaling, which requires application changes to implement read replicas or sharding. - This adds infrastructure (against requirements) and increases management complexity. - Even with reserved instances, maintaining multiple instances is more expensive than scaling up a single instance. **Option D (On-demand DB instance):** - Switching to on-demand pricing is actually more expensive than reserved instances for predictable workloads. - This doesn't address the performance scaling requirement - it only changes the billing model. **Key AWS Concepts:** - **Amazon RDS Scaling:** Vertical scaling (instance size) vs. horizontal scaling (read replicas) - **Pricing Models:** Reserved Instances (for predictable workloads) vs. On-Demand (for variable workloads) - **Cost Optimization:** Right-sizing instances and using reserved capacity for predictable workloads **Best Practice:** For predictable workload increases, scale vertically first (larger instance) with reserved instances for cost savings, then consider read replicas for read-heavy workloads if needed.

Author: LeetQuiz Editorial Team