A marketplace app stores item prices in DynamoDB with ElastiCache in front. Prices change frequently, and sellers report that after they update a price, the listing still shows the old price. What is the most likely cause?

The most likely cause is that the cache is not being invalidated when the item price changes. When an application uses a cache, it stores frequently accessed data to reduce latency and load on the primary data store (DynamoDB in this case). If the cache isn't updated or invalidated when the source data changes, users will continue to see stale data from the cache. This is a common issue with caching strategies. "The price is being retrieved using a write-through ElastiCache cluster" is incorrect because write-through caching updates the cache simultaneously with the database, which would prevent stale data. "Insufficient read capacity" or "insufficient write capacity" for DynamoDB would typically manifest as throttled requests or slower updates, not consistently displaying old prices after an update.