Data Storage choice is dictated to be non-relational due to high level of interconnection between non- homogeneous data such as “user likes user”, “user likes product X”, “comment about product X”, “comment about user”, etc. In order to simplify technology stack, best choices will be universal no-sql databases such as Cassandra, Neo4j, QuasarDB, Tarantool, or HBase.
Engine that powers messaging can either utilize functionality of RabitMQ as one of the most direct solutions or be implemented on top of data streaming technologies such as Apache Flume or Kafka.