NATS: Ultra-low Latency and Messaging Distributed System Used by Naver Interviewers

This course provides a step-by-step learning path, ranging from the fundamental usage of MySQL to advanced techniques required in real-world production environments. It covers a wide range of topics, including data modeling techniques based on various case studies and practical data, evaluating the effectiveness of Foreign Key designs, analyzing Google Calendar schema DDL, and modern DDL design principles. Through this course, you will gain an in-depth understanding of how to utilize MySQL as a core system component rather than just a simple database.

Most developers are still stuck on Batch and CronJobs when it comes to data processing. However, in real-world production environments, data is generated continuously, and failing to process that flow immediately leads to latency, bottlenecks, and consistency issues. Having personally dealt with real-time recommendations, state synchronization, and event delay problems in high-traffic environments, I’ve often asked myself, "Is batch processing really the right approach for this?" This course begins with that very question. It explores how to use Apache Flink to perform computations the moment data flows, manage state securely, and produce accurate results based on Event Time—all from a practical perspective. Beyond simple theoretical explanations, you will experience how real-time stream processing systems are designed and operated through actual source code and architectures. For those who found real-time processing vague or were curious about the world beyond messaging, this course will provide a clear sense of direction.

Learn how to design and process large-scale data architecture that handles hundreds of billions of data records using only pure SQL and MySQL's core features, together with a Toss developer who handles hundreds of billions of financial traffic transactions and a developer who started as a non-major and is now developing platforms in Pangyo.

This course covers RPC communication techniques that maximize performance in large-scale MSA (Microservice Architecture) environments. Going beyond simple gRPC practice, you'll learn how to implement stable and efficient inter-service communication in real production environments where hundreds of microservices operate simultaneously. Based on Golang, the course covers Protocol Buffers (proto) syntax writing, automatic code generation and service implementation, gRPC structure and advantages over existing RPC, and performance optimization strategies with a practical focus. To ensure easy understanding for non-majors and server development beginners, the course provides step-by-step explanations from RPC concepts to gRPC's internal operating principles, enabling you to develop practical skills that can be immediately applied to real services.

How do you handle exploding traffic? Learn how to build resilient and flexibly scalable architectures through practical design patterns based on EDA (Event-Driven Architecture) using Kafka, Spring, CDC, and Temporal. Explained clearly and simply with real-world experience from a Kakao developer, making it accessible even for non-majors. A hands-on, practical course covering real-time data flow, event processing, and microservice integration all at once!

Develop a scalable order processing system with real-time event streaming capabilities using Spring Boot 3.x + Kotlin to build a Kafka cluster, leveraging PostgreSQL CDC, Debezium Connect, and Apache Avro schema.

Learn SAGA transaction management techniques for maintaining data consistency in distributed environments through hands-on practice. Build 3 microservices using Spring Boot and Docker, and implement both Orchestration and Choreography patterns with Kafka and MySQL. Through this course, you can master core concepts that are immediately applicable in real-world scenarios, including distributed transaction operation principles, compensating transaction design, and failure recovery handling.

In this course, rather than directly covering theory, you will learn how to effectively use Redis in code through hands-on practice.

This course covers how to set up multi-module projects from scratch using Kotlin and Spring Boot. It proceeds with a hands-on approach, covering everything from the basic concepts of modularization to Gradle configuration, managing dependencies between modules, and actual application development. If you are a beginner or intermediate developer looking to learn the fundamentals and practical application of multi-modules, please refer to this course.

Learn the process of building essential Observability in a Microservices Architecture (MSA) environment from basics to practical application. Master standardized data collection using OpenTelemetry, trace storage and search through Grafana Tempo, and visualization using TraceQL through step-by-step hands-on practice. You can learn how to track service flows through distributed tracing, identify bottlenecks, and analyze the root causes of failures.

Learn the process of building data pipelines using Apache Airflow from basics to practical application. Understand Airflow's core concepts and architecture, and master advanced design patterns frequently used in practice such as dynamic DAGs, parallel processing, distributed processing, and Custom Operators through hands-on exercises. Set up a practice environment with Python and Docker, and develop practical skills to design and operate real workflows.

This course explores microservice architecture and distributed environments not as a simple list of technologies, but from a 'design perspective' required in actual work and interviews. Starting from the differences between monolithic and MSA, it progressively covers incremental migration strategies, modular monoliths, clean architecture and hexagonal architecture, clearly explaining why each choice is necessary and the trade-offs involved. Through hands-on practice, you can directly verify the intent of the structure and learn about core issues inevitably encountered in distributed environments—such as data consistency, transactions, inter-service communication, and failure handling—through realistic scenarios. Based on actual questions and perspectives from Kakao interviewers, this course aims to go beyond simple knowledge acquisition and elevate your way of thinking about distributed systems to the next level.

Using Spring Boot 3.x + Kotlin, we build a 3-instance cluster, and utilizing Redis Pub/Sub distributed messaging and an Nginx load balancer, develop a scalable WebSocket real-time chat server capable of handling large-scale traffic.

This course is a master class that systematically covers the fundamental principles and practical applications of MongoDB. Starting with core MongoDB concepts, you will systematically learn essential topics for practical work, such as database design, CRUD operations, indexing, aggregation pipelines, performance optimization, transactions, and security. It explains topics step-by-step so even beginners can understand, and you can deeply learn the working principles of MongoDB through exercises and examples. This is the best introductory and practical course for developers who want to build strong MongoDB skills for practical work.

This course is a master class that teaches Kotlin's 🌺 Coroutine, covering everything from theoretical foundations to practical application in a standard manner. It systematically covers core principles and structure, the necessity of asynchronous programming, Coroutine builders and scopes, exception handling, channels, Flow, and other key features frequently used in practice, step by step. Each concept is explained with hands-on examples, making it easy for beginners to understand and immediately apply them. This is the best introductory and practical course for developers who want to build strong Coroutine skills for real-world use.

Let's build a project using Ktor, the most popular project in Kotlin, and master Kotlin! 😆

Kotlin mastery via virtual payment server course.

I am covering the know-how on how I studied and got a job, starting as a non-major.

I'll show you how to use Redis effectively, along with its precautions and best practices, using real-world examples from actual work environments and well-known case histories.

You can learn about JWT and ws communication using Spring Boot, and how to handle high TPS.

Most developers are still stuck on Batch and CronJobs when it comes to data processing. However, in real-world production environments, data is generated continuously, and failing to process that flow immediately leads to latency, bottlenecks, and consistency issues. Having personally dealt with real-time recommendations, state synchronization, and event delay problems in high-traffic environments, I’ve often asked myself, "Is batch processing really the right approach for this?" This course begins with that very question. It explores how to use Apache Flink to perform computations the moment data flows, manage state securely, and produce accurate results based on Event Time—all from a practical perspective. Beyond simple theoretical explanations, you will experience how real-time stream processing systems are designed and operated through actual source code and architectures. For those who found real-time processing vague or were curious about the world beyond messaging, this course will provide a clear sense of direction.

Develop a scalable order processing system with real-time event streaming capabilities using Spring Boot 3.x + Kotlin to build a Kafka cluster, leveraging PostgreSQL CDC, Debezium Connect, and Apache Avro schema.

You can improve your Java programming skills by working on your own projects using various Java APIs and Open APIs.

We enable you to fundamentally understand and resolve issues where Hangeul appears broken on web pages or in databases, or files contain unknown characters.

An in-depth TypeScript course for top web developers. You'll grasp TypeScript's essence upon completion, mastering React, Next, Nest, and more.

A course that helps you understand core JavaScript concepts and practice explaining them verbally in interviews

Cultivate advanced programming language utilization skills and software design and implementation skills combining functional, object-oriented, and LISP paradigms, necessary for growing into a mid-to-senior level developer.

Kind Course even coding novices can follow! The ultimate course that makes working developers JavaScript experts!

"The Era of Coding with AI: A New Productivity Paradigm for Java Developers" This course is a practical Cursor AI utilization guide for Java developers. Beyond simply copying AI-generated code, you'll learn Vibe Coding methods that maximize development efficiency through collaboration with AI. By leveraging Cursor's powerful code understanding, refactoring, and documentation features, you'll master AI coding workflows step by step that can be immediately applied to real-world projects. In an era where AI writes code for us, "developers who can effectively work with AI" now have the competitive edge. Start your upgraded development experience as a Java developer with this course.

We will cover the concept of machine learning in a JavaScript environment. We will cover the form and code of implementing machine learning with JavaScript and TensorFlow.js.

Instead of long and boring theories, you can learn them one by one through short practical exercises, and as you flesh them out one by one, you will soon be able to experience the overall architecture composition.

This course systematically teaches from JavaScript synchronous/asynchronous concepts, asynchronous processing methods incorporating the latest syntax such as Promise and async/await, and practical HTTP communication.

New to React? You need to think about how to learn React's fundamental concepts solidly yet quickly. Start with Next.js and JavaScript with minimal knowledge. Let's develop by selecting only the essential examples needed for real-world development. The Todo example is so important that you should develop it twice. Once focusing on components, and then focusing on routing that handles browser paths! Use Zustand for login! You can handle global state with a really small amount of code.

Spring AI + JPA + MySQL Premium Reservation Agent Backend Development with 'Autonomous Behavior' Beyond Chatbots to Agents: The Definitive Guide to Tool Calling and Prompt Engineering

Experience the power of Type Safe SQL with jOOQ!

You can understand the JavaScript engine V8! You can get hints on how to write more efficient code.

I've created a CI/CD introductory course that's easy to understand even for non-majors and can be applied immediately in real-world situations!

This article introduces the relationship between Nodejs, a server-side JavaScript language, and a database, and explains how to create web applications using Nodejs and a database.

An AI system that grades and reviews your code in 5 seconds - imagination becomes reality. This course is an all-in-one project that builds a **'GitHub PR Automatic Analysis and Grading Bot'** using Spring AI. When a student submits an assignment (Pull Request), the server detects it and AI analyzes the code changes (Diff). The grading results are then stored in the database, feedback is automatically posted as GitHub comments, and students can check their results on a dedicated dashboard. From backend to AI integration and frontend (Vaadin) - all with Java! This is the ultimate introductory guide for all developers who want to complete their own AI service from A to Z.

We will systematically learn essential theories such as Motivation, History, Structure, and Life Cycle required for Docker and Dockerizing. Above all, by participating in three solid hands-on code labs, you will become a developer who is most confident about Docker.