Topic

A topic is a logical stream of events.

It is similar to:

• a table (append-only)
• a category of events

Example

customer.created.v1
account.created.v1
account.transaction.v1

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Real Microservice Example

Order Service → order.created.v1 topic

Consumers:

• Payment Service
• Inventory Service
• Notification Service

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Why Topics Exist

• organize data
• separate event types
• allow multiple consumers

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How Topic Works Internally

A topic is NOT a single file.

Topic → Partitions

A topic is split into multiple partitions.

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Kafka CLI — Create Topic

kafka-topics.sh
  --create
  --topic order.created.v1
  --partitions 3
  --replication-factor 1
  --bootstrap-server localhost:9092

using Spring boot

package com.bank.customer.config;

import org.apache.kafka.clients.admin.NewTopic;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.kafka.config.TopicBuilder;

@Configuration
public class KafkaTopicConfig {

    @Bean
    public NewTopic customerCreatedTopic() {
        return TopicBuilder.name("customer.created.v1")
                .partitions(3)
                .replicas(1)
                .build();
    }

}

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Verify Topic

kafka-topics.sh --list --bootstrap-server localhost:9092

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Best Practices

Good:

• order.created.v1
• payment.completed.v1

Avoid:

• topic1
• test

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