DynamoDB = a database. This is a general purpose tool for storing data to retrieve later. It is an AWS managed service which means Amazon will handle the actual infrastructure the database runs on for you. It has some limited querying capability. redis = an in memory data-store. Similar to a database but the data is less permanent. Most people use it as a cache because it provides fast lookup times. Redis is an open source product so you can run it yourself or let a cloud provider run it for you. It has the least querying capability. memcached = similar to redis. Older technology. elasticache = an AWS managed cache service. Basically Amazon will create a redis or memcached instance for you. You don’t need to worry about the infrastructure the cache runs on. elasticsearch = search software. Technically this is an open source tool but Amazon has a managed version with the same name. You use elasticsearch if you want an extreme amount of querying capability. It is also the slowest.

There are two type of Redis deployment in AWS ElastiCache service:

1. Standalone
2. Multi-AZ cluster

With standalone installation it is possible to turn on persistence for a Redis instance, so service can recover data after reboot. But in some cases, like underlying hardware degradation, AWS can migrate Redis to another instance and lose persistent log.

In Multi-AZ cluster installation it is not possible to enable persistence, only replication is occur. In case of failure it takes a time to promote replica to master state. Another way is to use master and slave endpoints in the application directly, which is complicated. In case of failure which cause a restart both Redis node at time it is possible to lose all data of the cluster configuration too.

So, in general, Redis doesn't provide high durability of the data, while gives you very good performance.

DynamoDB is highly available and durable storage of you data. Internally it replicates data into several availability zones, so it is highly available by default. It is also fully managed AWS service, so you don't need to care about Clusters, Nodes, Monitoring ... etc, which is considering as a right cloud way.

Dynamo DB is charging by R/W operation (on-demand or reserved capacity model) and amount of stored data. In may be really cheap for testing of the service, but much more expensive under the heavy load. You should carefully analyze you workload and calculate total service costs.

As for performance: DynamoDB is a SSD Database comparing to Redis in-memory store, but it is possible to use DAX - in-memory cache read replica for DynamoDB as accelerator on heavy load. So you won't be strictly limited with the DynamoDB performance.

Here is the link to DynamoDB pricing calculator which one of the most complicated part of service usage: https://aws.amazon.com/dynamodb/pricing/

From the description, it sounds like you are looking for a solution where you could temporarily cache data that can be consumed (read-only) by an API. Redis seems to be a potential fit, you could also look at Memcached. Below document has a comparison of Memcached and Redis https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/SelectEngine.html Having said this, I would recommend you to review the requirement in a bit more detail and make a choice. Here are some areas you could think of and some questions you could ask yourselves (Not an exhaustive list) - 1. What is the type and structure of data? What is the volume of data? A reference on evaluating DynamoDB - https://aws.amazon.com/blogs/database/how-to-determine-if-amazon-dynamodb-is-appropriate-for-your-needs-and-then-plan-your-migration/ Redis is also a key-value pair data store. 2. How often this data changes? Can the external source propagate the incremental data changes to AWS i.e. Do you really need a daily full dump or incremental delta feeds? 3. Would persisting this data in RDS or DynamoDB serve any of your long term goals? (Based on the volume of reads, this could be a combination of 'RDS and Redis' or 'DynamoDB & DAX')? 4. What is the request volume? What volumes of requests query for same data as response (i.e. repeated reads)? 5. Do you have an API gateway for the API and does that already cache the API responses? Also, do you have any CDN (Content Delivery Network) already caching the API responses. 6. What are the data encryption/security, back-up and recovery (RTO and RPO), availability, durability requirements? Use the below cost calculator to create an estimate for these 3 services to compare. Make sure you also consider the opportunity of reservations for these services - https://calculator.aws/#/

Redis is lower latency and doesn’t have a pay-per-request price scheme like dynamo does. Your use case may rule either of these points out, but those are the first two things I’d tell someone on my team if they asked the question.