Kafka Broker Configuration (server.properties)

---

1. Broker Basics

broker.id=1
listeners=PLAINTEXT://localhost:9092
log.dirs=/var/lib/kafka/data

• broker.id → unique broker identifier
• listeners → host/port Kafka listens on
• log.dirs → storage location for Kafka data

If log.dirs disk is full → Kafka stops working

---

2. Topic Defaults

num.partitions=3
default.replication.factor=3
min.insync.replicas=2

• partitions → parallelism
• replication.factor → fault tolerance
• min.insync.replicas → durability guarantee

---

3. Storage & Retention

log.segment.bytes=1073741824
log.retention.hours=168
log.retention.bytes=10737418240
log.cleanup.policy=delete

• segment size → file chunking
• retention → data lifetime
• cleanup.policy → delete / compact

---

4. Compaction Support

log.cleaner.enable=true
log.cleaner.threads=2

Used when:

cleanup.policy=compact

---

5. Replication Safety

unclean.leader.election.enable=false

• prevents data loss during leader election

---

6. Message Size Limits

message.max.bytes=1048576
replica.fetch.max.bytes=1048576

• max message size Kafka accepts

---

7. Network & Threads

num.network.threads=3
num.io.threads=8
socket.send.buffer.bytes=102400
socket.receive.buffer.bytes=102400

• controls throughput and performance

---

8. Offset Topic

offsets.topic.replication.factor=3

• ensures consumer offset safety

---

9. Topic Creation Control

auto.create.topics.enable=false

• prevents accidental topic creation

---

10. Optional Flush Config

log.flush.interval.messages=10000
log.flush.interval.ms=1000

• usually not required (Kafka optimized already)

---

11. Zookeeper / KRaft

Zookeeper mode

zookeeper.connect=localhost:2181

KRaft mode

• no zookeeper required

---

12. Recommended Production Configuration

# Reliability
default.replication.factor=3
min.insync.replicas=2
unclean.leader.election.enable=false

# Storage
log.retention.hours=168
log.segment.bytes=1073741824

# Safety
auto.create.topics.enable=false

# Offsets
offsets.topic.replication.factor=3

---

13. Producer Mapping

Producer Config	Broker Config
acks=all	min.insync.replicas=2
retries	replication.factor
idempotence	durability

---

Final Understanding

Kafka Broker Config (server.properties) controls:

• durability
• storage
• replication
• system safety

Application config controls:

• how your app interacts with Kafka