Scenario Based Interview Question — 4

In the realm of data management, the ability to maintain a comprehensive history of changes is crucial for many applications. A recent exploration into this topic reveals a sophisticated approach utilizing an event-driven architecture that leverages Kafka alongside MongoDB and PostgreSQL. This method not only ensures real-time tracking of data changes but also provides a robust mechanism for auditing and compliance.

Real-Time Tracking Using PostgreSQL Triggers + Kafka

  • A PostgreSQL trigger is established on the customer table to monitor changes, including INSERT, UPDATE, and DELETE operations.
  • This trigger utilizes the LISTEN/NOTIFY mechanism to publish changes.
  • A Spring Boot listener, known as CustomerChangeListener, is set up to continuously monitor these database changes.
  • Upon detecting a change, the event is transformed into a structured format and sent to Apache Kafka via the KafkaProducerService.

Event-Driven Processing Using Kafka (Pub-Sub Model)

  • A dedicated Kafka topic, customer_events, is created to manage the stream of customer change events.
  • The Kafka producer, KafkaProducerService, is responsible for publishing these customer change events.
  • A Kafka consumer, KafkaConsumerService, listens for new events as they arrive.
  • Upon receiving an event, it is stored in a MongoDB collection named customer_history.

Persisting Change History in MongoDB

  • The MongoDB customer_history collection serves as the repository for all historical customer changes.
  • Each record captures details about who made the change, what was altered, when it occurred, and the rationale behind it, thereby ensuring a complete audit trail.
  • This structure allows for straightforward querying of audit logs, facilitating tracking and compliance efforts.

To implement this architecture, one must first establish a project structure that accommodates the necessary components, including the database files. The Maven pom.xml file should be updated with all required dependencies, such as Spring Boot, PostgreSQL, MongoDB, and Kafka.

Project Setup

After setting up the project structure, the application properties must be configured to connect to the PostgreSQL and MongoDB databases, as well as to the Kafka broker. This includes specifying the server port, database URLs, and other relevant configurations.

Main Application File: CustomerTrackingApplication.java

package com.example.customertracking;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class CustomerTrackingApplication {
    private static final Logger logger = LoggerFactory.getLogger(CustomerTrackingApplication.class);

    public static void main(String[] args) {
        SpringApplication.run(CustomerTrackingApplication.class, args);
        logger.info("Customer History Service is running...");
    }
}

Controller Package

The CustomerController.java file manages the CRUD operations for customer data, ensuring that each operation triggers the appropriate database actions and Kafka notifications.

Service Package

The CustomerService.java file encapsulates the business logic for managing customer data, interacting with both the PostgreSQL database and Kafka for event handling.

DB Trigger

To facilitate change tracking, a history table must be created in PostgreSQL, along with a trigger that executes upon any changes to the customer table. This ensures that all modifications are logged appropriately.

Listener Package

The CustomerChangeListener.java file listens for notifications from PostgreSQL, processes them, and sends the relevant data to Kafka for further handling.

Kafka Service Package

The Kafka producer and consumer services are responsible for sending and receiving messages related to customer changes, ensuring that the history is accurately reflected in MongoDB.

MongoDB Storage

All changes, whether insertions, updates, or deletions, are stored in the customer_history collection in MongoDB, providing a comprehensive record of customer interactions.

Through this architecture, organizations can achieve a seamless integration of real-time data tracking and historical record-keeping, enhancing their ability to manage customer relationships effectively. The combination of PostgreSQL, Kafka, and MongoDB creates a powerful framework for any data-centric application.

Tech Optimizer
Scenario Based Interview Question — 4