Consumer Configuration

Introduction

What is Consumer Configuration? Consumer config controls group identity, offset reset, commit behavior, max poll size, session timeout, and partition assignment strategy.

Understanding the topic

What happens — Consumer Configuration:

• group.id identifies the consumer group.
• enable.auto.commit=false for manual control.
• auto.offset.reset for new groups.
• max.poll.interval.ms limits processing time.

Visual explanation

Pipeline view:

Consumer polls records from topic partitions
  ↓
Process business logic (DB, API, etc.)
  ↓
Commit offset after success
  ↓
Monitor consumer lag

Step-by-step explanation

1. Subscribe — Consumer joins a group and receives partition assignments.
2. Poll — Fetch records in batches with consumer.poll().
3. Process — Run business logic for each record.
4. Commit — Save offset after successful side effects.
5. Repeat — Continue polling; rebalance if group membership changes.

Informative example

Example:

group.id=inventory-service
enable.auto.commit=false
auto.offset.reset=earliest
max.poll.records=500
session.timeout.ms=45000
partition.assignment.strategy=org.apache.kafka.clients.consumer.CooperativeStickyAssignor

Execution workflow

Best practices

• Use manual commits for critical side effects.
• Make consumers idempotent with event IDs or unique constraints.
• Keep processing under max.poll.interval.ms or use pause/resume patterns.
• Send poison messages to DLT with failure metadata.

Common mistakes

• Committing before database writes complete.
• Scaling consumers beyond partition count and expecting more throughput.
• Blocking the poll loop with slow downstream calls.

Summary

Consumer Configuration — Commit offsets only after successful processing; make handlers idempotent; monitor lag per partition.