CosmosDB

CosmosDB is a fully managed NoSQL DB on Azure. It supports five APIs namely:

1. Core(SQL) API
2. MongoDB
3. Cassandra
4. Gremlin
5. Table

In AWS DynamoDB, you only have to create a Table to start using a NoSQL DB.

In CosmosDB, you need to understand the billing model to make a resource decision. Things to consider include:

1. Provisioned throughput - billed 100 RU/s (request units) or Serverless - billed per hour.
2. Throughput autoscale or manual scaling.
3. Granularity to manage througput - the database or container level

One database can share throughput with multiple containers. But each container can have its dedicated throughput for predictable performance.

DocumentDB vs MongoDB

Apparently DocumentDB is an emulation of the MongoDB API with many limitations.