What is Kafka replication, and why does it matter?

Each partition can be configured with a replication factor N, meaning N total copies of that partition's data are stored across different brokers — one is the leader (handles all reads/writes) and the rest are followers (passively replicate from the leader). If the leader broker fails, one of the in-sync followers is automatically promoted to leader, which is what gives Kafka its durability and fault tolerance without any data loss for committed messages.