DocumentDB is a fully managed non-relational document database, with full MongoDb compatibility, that means it is very useful for JSON data, it is able to scale automatically up to 64TB.

Cluster endpoint - for apps that require both read and write -access to the database

Reader endpoint: used to connect to read replicas

Instance Endpoint: every instance within your cluster, including your primary and read replica instances, will each have their own unique instance endpoint that will point to itself. Useful for load-balancing reasons.