Amazon MemoryDB vs. Amazon DocumentDB

Amazon MemoryDB for Redis is a Redis-compatible, durable, in-memory database that delivers ultra-fast performance and Multi-AZ durability. With Amazon MemoryDB for Redis, you only pay for what you use with no minimum fee. A node is the smallest building block of a MemoryDB cluster. Each node supports varying amounts of computation and memory capacity, and you can select a node type based on your needs. You are charged based on three components: on-demand instance hours per node, volume of data written to your cluster, and snapshot storage that you use.

Amazon DocumentDB (with MongoDB compatibility) is a database service that is purpose-built for JSON data management at scale, fully managed and integrated with AWS, and enterprise-ready with high durability. Amazon DocumentDB is designed from the ground-up to give you the scalability and durability you need when operating mission-critical MongoDB workloads. In Amazon DocumentDB, storage scales automatically up to 64TiB without any impact to your application.