Which solutions meet these requirements?

Explanations:

AWS Storage Gateway Volume Gateway provides block storage over iSCSI, which is not ideal for shared access across multiple EC2 instances in different Availability Zones. EBS volumes can only be attached to a single EC2 instance at a time, making this solution unsuitable for the requirement of strong consistency and shared access.

Amazon EFS provides a fully managed, scalable, shared file storage solution that can be mounted across multiple EC2 instances in different Availability Zones. It offers strong consistency, meaning changes made to the content are immediately visible to all instances. This aligns with the application’s requirement for frequent content changes.

A shared Amazon EBS volume cannot be attached to multiple EC2 instances simultaneously. EBS volumes can only be mounted by one instance at a time, which does not meet the need for a shared storage solution accessible by multiple instances across different Availability Zones.

AWS DataSync is a service for transferring large amounts of data between on-premises storage and AWS, or between AWS storage services. It does not provide real-time or strong consistency for applications running in an Auto Scaling group, as it relies on batch synchronization rather than continuous access to shared data.

Amazon S3 can store web content with strong consistency, and setting the Cache-Control header to no-cache ensures that the content is always fetched fresh. Using Amazon CloudFront as a CDN allows for fast content delivery while maintaining the latest content availability. This solution effectively meets the requirement for strong consistency with frequent updates.