For Cloud-Native development we can leverage different database types based on the need. There is no need to get stuck with one type of database for the entirety of the application.
To store relationship of Friends or Order System you typically start with relational database like MySQL or PostgresSQL. For Low-latency access for frequently accessed data we can use a key-value Database like Redis, Memcache. We can use to store sessions. For analytics , we can use Wide-Column database like Cassandra or HBase. For recommendation system with relationships, a graph database would do the job.