Kafka Consumer Rebalance
Watch partition rebalancing across a consumer group as members join and leave.
Consumers
3
Partitions
8
Moved
0
Rebalance
Stable
Assigned Moved this rebalance
Consumer 0
036
Consumer 1
147
Consumer 2
25
Add or remove a consumer and every partition reassigns at once (a stop-the-world pause). The red edges and * marks show which partitions moved. More partitions than consumers lets you scale out without leaving consumers idle.
How this simulator works
A consumer group reassigns partitions whenever membership changes. Every rebalance is a stop-the-world pause — fewer, smoother rebalances keep throughput high.
What triggers a rebalance
- A consumer joins or leaves (scale up/down, crash, deploy).
- A partition is added to the topic.
- During a rebalance all consumption stops until assignment completes.
Minimizing pain
- More partitions than consumers lets you scale out without idle members.
- This simulator uses round-robin assignment, so every membership change reassigns ALL partitions.
- Sticky assignors (not modeled here) keep most partitions put, moving only what must move.