What is partition reassignment and when do you need it?

Partition reassignment moves partitions between brokers for: cluster expansion (add brokers then redistribute), decommissioning brokers, fixing uneven load distribution, or improving fault isolation (rack awareness). Use kafka-reassign-partitions.sh with --generate to plan and --execute to run. During reassignment, Kafka replicates each partition to its new broker while keeping the old replica available — this is live migration with no downtime. Monitor kafka.server:ReassignmentThroughput during reassignment to avoid saturating broker network.

Expected key concepts: partition reassignment, kafka-reassign-partitions.sh, cluster expansion, decommission, load distribution, rack awareness, live migration, no downtime, ReassignmentThroughput