EC2 Auto Scaling warm pools allow you to pre-initialize instances, reducing the delay in scale-out events.
This results in significantly faster response times during demand surges while remaining cost-effective compared to always running at peak capacity.
Reference: AWS Documentation - EC2 Auto Scaling Warm Pools for Faster Scaling

Express Workflows in AWS Step Functions are optimized for high-throughput, short-duration, and low-cost workflows. They are suitable for applications with large volumes of parallel and interdependent tasks. When paired with HTTP APIs from API Gateway, which are more cost-efficient than REST APIs, this setup offers scalability and cost-effectiveness.
Reference: AWS Documentation - Step Functions Express Workflows vs. Standard Workflows

Key Requirements:
* High availability and automatic recovery.
* Separate transactional and analytical queries with minimal performance impact.
* Allow up to a 4-hour lag for analytical queries.
Analysis of Options:
* Option A:
* Multi-AZ deployments provide high availability but do not include read replicas for separating transactional and analytical queries.
* Analytical queries on the secondary DB instance would impact the transactional workload.
* Incorrect Approach: Does not meet the requirement of query separation.
* Option B:
* Multi-AZ DB clusters provide high availability and include a reader endpoint. However, these are better suited for Aurora and not RDS for MySQL.
* Incorrect Approach: Not applicable to standard RDS for MySQL.
* Option C:
* Multiple read replicas allow separation of transactional and analytical workloads.
* Queries can be pointed to a replica in a different AZ, ensuring no impact on transactional queries.
* Correct Approach: Meets all requirements with high availability and query separation.
* Option D:
* Creating nightly snapshots and read-only databases adds significant operational overhead and does not support the 4-hour lag requirement.
* Incorrect Approach: Not practical for dynamic query separation.
AWS Solution Architect References:
* Amazon RDS Read Replicas
* Multi-AZ Deployments

* AWS Outposts brings native AWS services (including Amazon EMR) on-premises, ideal when data residency or latency constraints require local processing.
* You benefit from AWS's managed services while meeting the requirement to keep data processing local.
References:
Amazon EMR on AWS Outposts

AWS recommends multi-Region active-active architectures for applications requiring high availability, automatic failover, and disaster recovery. Route 53 latency-based routing directs users to the Region providing the lowest latency and automatically shifts traffic if Regional endpoints become unhealthy.
Combined with Application Load Balancers and EC2-based microservices deployed in multiple Regions, this architecture delivers fault tolerance, multi-Region resiliency, and automatic recovery.
Option D provides high availability but does not inherently provide multi-Region failover routing without additional configuration. Option B is single-Region. Option A is not resilient.