In a highly available MongoDB environment, where can we read and write data?

In a highly available MongoDB environment, data can be read from and written to the primary member of the replica set. The primary member is the main node in a MongoDB deployment that handles all write operations and reads by default unless otherwise configured. This ensures that the primary member maintains the most up-to-date data.

When operating in a replica set, secondary members can be used for read operations if configured for such, but they cannot accept write operations. This design helps distribute read loads while maintaining consistency through writes that occur only on the primary.

In the context of sharded clusters, while you can read and write data, those actions typically involve interaction with multiple primary shards and may not provide the same simple read/write interface as a single replica set's primary.

Thus, the primary member's role is crucial in a highly available MongoDB architecture for managing data integrity and consistency during write operations.