Event Streaming with Kafka

OmniNet uses Apache Kafka in KRaft mode (no ZooKeeper) for asynchronous, decoupled event streaming between services.

Event Topics

Topic	Producer	Consumers	Purpose
omninet.user.created	auth-service	storage-service, notes-service	Provision user folders in S3 and default note categories
omninet.user.updated	auth-service	storage-service	Propagate profile changes
omninet.file.events	storage-service	storage-service	Quota reconciliation on upload/delete
omninet.note.events	notes-service	—	Note change auditing
omninet.todo.reminders	notes-service	—	Todo reminder dispatch from scheduler

Event Flow — User Registration

Event Schema — UserCreatedEvent

public record UserCreatedEvent(
    String userId,
    String email,
    String firstName,
    String lastName,
    Instant createdAt
) {}

Kafka Configuration

Property	Value
Mode	KRaft (no ZooKeeper)
Compression	none (configurable via KAFKA_COMPRESSION_TYPE)
Bootstrap	localhost:9092 (local) / omninet-kafka:9092 (Docker)
Topic replication	1 (development)
Consumer group prefix	omninet-*

NOTE

Kafka compression was set to none because Alpine Linux containers use musl libc, which is incompatible with Snappy's native JNI library.

Producer Error Handling

All Kafka producers wrap publish calls in try-catch blocks to prevent Kafka failures from blocking the main request flow:

try {
    kafkaTemplate.send(topic, event);
} catch (Exception e) {
    log.error("Failed to publish Kafka event: {}", e.getMessage());
    // Non-fatal — main operation already completed
}