Explanation

To achieve high availability for an application hosted on Amazon EC2 instances, the instances should be deployed across multiple Availability Zones (AZs). Here's why:

Key Concepts:

• Availability Zones (AZs):
  • Each AZ is a physically separate data center within an AWS Region
  • AZs are designed to be isolated from failures in other AZs
  • Deploying across multiple AZs provides fault tolerance and high availability

Why Multiple AZs Provide High Availability:

1. Fault Isolation: If one AZ experiences an outage, the application can continue running from other AZs
2. Automatic Failover: Load balancers can distribute traffic across instances in multiple AZs
3. Redundancy: Data and services are replicated across different physical locations

Why Other Options Are Incorrect:

• Multiple Edge Locations: Edge locations are for content delivery (CloudFront), not for hosting EC2 instances
• Multiple VPCs: While VPCs provide network isolation, they don't inherently provide high availability across different physical locations
• Multiple AWS Accounts: This is for organizational/security separation, not high availability

Best Practice:

For maximum availability, deploy EC2 instances across at least 2-3 Availability Zones and use an Elastic Load Balancer to distribute traffic evenly.