Answer: Migrate the application layer to Amazon EC2 Reserved Instances. Migrate the data storage layer to Amazon Aurora Reserved Instances.

## Explanation **Correct Answer: C** **Why Option C is correct:** 1. **Application layer (EC2 Reserved Instances):** Since the application runs 24/7, using Reserved Instances provides the most cost-effective option compared to On-Demand pricing. Reserved Instances offer significant discounts (up to 72%) for steady-state workloads with predictable usage patterns. 2. **Database layer (Amazon Aurora Reserved Instances):** Aurora is a MySQL and PostgreSQL-compatible relational database that offers better performance and cost-effectiveness than standard RDS. Using Reserved Instances for Aurora provides the same cost benefits as EC2 Reserved Instances for the database tier. 3. **Growing storage:** Aurora automatically scales storage up to 128 TiB, which addresses the requirement that "database storage continues to grow over time." **Why other options are incorrect:** **Option A:** - EC2 Spot Instances are not suitable for 24/7 applications as they can be interrupted with short notice - Amazon S3 is object storage, not suitable for a relational database workload **Option B:** - EC2 Reserved Instances are correct for the application layer - RDS On-Demand Instances are more expensive than Reserved Instances for 24/7 workloads **Option D:** - EC2 On-Demand Instances are more expensive than Reserved Instances for continuous workloads - RDS Reserved Instances are correct for the database layer, but Aurora Reserved Instances would be more cost-effective and scalable **Key AWS Concepts:** - **Reserved Instances:** Provide significant cost savings (up to 72%) for predictable workloads - **Amazon Aurora:** MySQL/PostgreSQL-compatible database with better performance, scalability, and cost-effectiveness than standard RDS - **Cost optimization:** For 24/7 workloads, Reserved Instances are always more cost-effective than On-Demand or Spot Instances

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