A company runs a three-tier web application in the AWS Cloud that operates across three Availability Zones. The application architecture has an Application Load Balancer, an Amazon EC2 web server that hosts user session states, and a MySQL database that runs on an EC2 instance. The company expects sudden increases in application traffic. The company wants to be able to scale to meet future application capacity demands and to ensure high availability across all three Availability Zones. Which solution will meet these requirements?

The correct solution addresses all requirements for scalability and high availability. Migrating the MySQL database to Amazon RDS for MySQL with a Multi-AZ DB cluster deployment ensures high availability and automatic failover for the database layer. Using Amazon ElastiCache for Redis with high availability is ideal for storing session data and caching reads, as Redis supports complex data structures and high-performance caching. Migrating the web server to an Auto Scaling group spanning three Availability Zones provides automatic scaling to handle traffic spikes and distributes instances for high availability. Incorrect options: Using ElastiCache for Memcached is less suitable for session state management compared to Redis, which offers more advanced data structures and persistence options. Migrating to DynamoDB for the database and session data would require significant application re-architecture, as the current database is MySQL. While DynamoDB is highly scalable, it's a NoSQL database, and the question implies a relational database is currently in use. Using Amazon RDS for MySQL in a single Availability Zone does not provide high availability for the database, failing to meet a key requirement.