Klag vs Cruise Control

Klag and Cruise Control are not alternatives — they operate on different halves of cluster operations. Klag observes (read-only consumer lag), Cruise Control acts (rebalances partitions and heals the cluster). A healthy setup often uses both: Klag tells you something is wrong, Cruise Control fixes a class of those problems.

What each tool is

Klag is a read-only consumer-lag exporter. It never changes cluster state — it requires only DESCRIBE and emits metrics.
Cruise Control is a cluster-balancing and self-healing tool. It analyzes broker load and partition distribution and executes partition reassignments to rebalance data, add/remove brokers, and fix skew. It performs write/admin operations on the cluster.

At a glance

	Klag	Cruise Control
Category	Lag observer (read-only)	Cluster rebalancer (read-write)
Acts on the cluster	❌ (metrics only)	✅ (reassigns partitions)
Consumer lag	✅	❌ (broker-load focus)
Kafka permissions	`DESCRIBE` only	Admin / alter
Runtime	Java / Vert.x / GraalVM	Java
License	Apache 2.0	BSD 2-Clause

Different problems

Question	Tool
“Is a consumer group falling behind?”	Klag
“Will lag exceed retention before we catch up?”	Klag
“Are partitions unevenly distributed across brokers?”	Cruise Control
“Rebalance the cluster / drain a broker”	Cruise Control

Klag’s hot partition detection can flag a partition with abnormal throughput — a symptom — but Klag will never move a partition. Remediating broker/partition skew is exactly Cruise Control’s job.

When to use which

Use Cruise Control to fix broker imbalance and partition skew, or to automate broker add/remove and self-healing.
Use Klag to watch consumer lag and its trajectory (velocity, time-based lag, retention risk) and alert before consumers fall too far behind.

Because Klag is strictly read-only, it’s safe to run alongside Cruise Control: it can’t interfere with reassignments — it just reports what lag is doing while they happen.

Spotted something out of date? Open an issue or PR against website/ and we’ll fix it.