Maintaining an e-commerce website with a large product catalog and global customer base can be challenging. The catalog should be searchable, and individual product pages should contain a rich information set that includes, for example, images, a PDF manual, and customer reviews.
Customers want to find the products they are interested in quickly, and they expect pages to load quickly. Worldwide customers want to be able to make purchase at any time, so the website should be highly available. Meeting these challenges becomes harder as your catalog and customer base grow.
On above diagram, the role of Amazon ElastiCache is to store sessions for volatile data and cache the product catalog to reduce I/O (and cost) on DynamoDB.