What is consumer lag and why does it matter?
⚡
Quick Answer
Lag is the difference between the latest offset and the consumer's committed offset — how far behind processing is.
Detailed Answer
Growing lag means consumers can't keep up with producers, delaying downstream processing. Monitor it per partition/group (e.g. kafka_consumergroup_lag) and alert on sustained growth. Fixes include adding consumers (up to partition count), optimizing processing, or increasing partitions.
💡
Interview Tip
Sustained lag growth is the alert-worthy signal.
kafkalagmonitoring