Answer: Modify the Auto Scaling group to use three instances across each of two Availability Zones.

## Explanation **Correct Answer: B** **Why Option B is correct:** 1. **High Availability within a Region**: Distributing instances across multiple Availability Zones (AZs) within the same AWS Region provides high availability against AZ-level failures. 2. **No Application Modification Required**: This solution maintains the same application architecture while improving resilience. 3. **Auto Scaling Group Configuration**: By configuring the Auto Scaling group to use three instances across each of two AZs (total of 6 instances), the solution maintains the same total capacity while providing redundancy. 4. **ALB Integration**: The Application Load Balancer can automatically distribute traffic across instances in multiple AZs and handle health checks. **Why other options are incorrect:** **A. Create an Auto Scaling group that uses three instances across each of two Regions.** - This creates a multi-region architecture which is more complex and may require application modifications for data synchronization and failover. - Multi-region deployment typically requires additional components like Route 53 for DNS failover and may involve data replication challenges. - This is overkill for achieving high availability within a single region. **C. Create an Auto Scaling template that can be used to quickly create more instances in another Region.** - This only provides a template for disaster recovery but doesn't implement active high availability. - The infrastructure would still be vulnerable to AZ failures in the primary region. - This is a reactive approach rather than a proactive high availability solution. **D. Change the ALB in front of the Amazon EC2 instances in a round-robin configuration to balance traffic to the web tier.** - Round-robin configuration is a load balancing algorithm, not a high availability solution. - This doesn't address the single point of failure issue of having all instances in one Availability Zone. - The ALB already performs load balancing; changing the algorithm doesn't improve availability. **Key AWS Concepts:** - **Availability Zones (AZs)**: Physically separate data centers within an AWS Region with independent power, cooling, and networking. - **High Availability**: The ability of a system to remain operational even when some components fail. - **Multi-AZ Deployment**: Distributing resources across multiple AZs protects against AZ-level failures. - **Application Load Balancer (ALB)**: Can distribute traffic across instances in multiple AZs and perform health checks to route traffic only to healthy instances. **Best Practice**: For high availability, always distribute resources across at least two Availability Zones within a Region to protect against AZ-level failures.