- "It became much faster by using Redis."
- They cannot explain "why they used it."
- When follow-up questions start, they crumble.
3-Day Intensive Backend Interview Core Guide [Na-Ka-Ra-Ku-Bae-Dang-To]
"I have a backend technical interview in a week—where should I start?" The secret to answers that make interviewers nod in approval. Fully master the actual answer patterns of successful candidates from Naver, Kakao, Coupang, and Toss in just 3 days!
673 learners
Level Basic
Course period Unlimited


Reviews from Early Learners
5.0
5.0
마젠토브힘내부왕
I'm someone who failed 13 interviews in a row. While watching the interview lecture, I realized how lacking I am, even though I don't fully understand it yet😢 I'll work hard until I understand it.
5.0
jy
I was able to resolve the parts that felt overwhelming while preparing for a career move, and through the lectures, I realized which areas I was lacking in. Thank you for the great lecture!
5.0
bshookhu
I paid four days before my interview. I'll complete the course and make sure to do well and share the good news of my acceptance! Thank you for the great lecture.
What you will gain after the course
Practical measurement methods for expressing project experience numerically
Advanced response tree for handling up to 2-3 follow-up questions
Practical mock interview simulation experience
It is not those who memorize questions, but those who can explain the 'why'
who pass.
For those who get stuck on follow-up questions after giving abstract answers like "I"ve used Redis." We condense behavioral interviews (experience) and technical interviews (concepts) into 3 days to build a winning answer structure.
The problem is not your knowledge, but the structure of how you explain the 'why'.
If you know the technology but can't explain it, give abstract answers, and get stuck on follow-up questions — you don't need to memorize more; you need to fix your answer structure.
It stops at "I've used Redis" or "I improved performance."
You can't answer questions like "Why did you choose this?" or "What were the alternatives?"
You have experience using the technology, but you cannot provide the reasoning for "why you used it."
Passing answers, with 6 weapons.
The unique differentiation of this lecture — we present the ABC answer formula, the 5 stages of 'Why', 7 patterns of follow-up questions, survival skills, corporate DNA, and numerical transformation like a spread of cards.
"It got a lot faster" is all I can say.
Problem → Solution → Improvement Metrics in a single-line formula.
I answered, "I wrote it to learn."
"I had to use it" — Provide the basis for your choice.
I get stuck on "Why did you choose this? Were there any other methods?"
Prepare in advance with 7 patterns..
"What if I really don't know?"
Instead of silence, narrow down the scope and show your thought process (K8s→Docker).
"I don't have any information about the company, so how can I appeal to them..."
Prepare interview tendencies by company + reverse questions.
"There is nothing to quantify."
Toido creates metrics through K6 load testing.
If this question comes up, answer like this.
Index, Transaction Isolation, Lock, Cache, JPA — we explain these common technical interview questions through analogies and show you exactly how to answer them when they come up.
"How does a B-Tree index work?"
Answer that it is a sorted tree, making it strong for range queries and sorting. nên có ưu thế trong việc truy vấn phạm vi và sắp xếp.
"Please explain isolation levels."
Explain it as a trade-off between concurrency and consistency.
"What is the difference between pessimistic and optimistic locking?"
Use pessimistic if conflicts are frequent, and optimistic if they are rare.
"What about Redis and DB consistency?"
Explains why Cache Aside is the default. là cơ bản.
"What if the cache explodes?"
With responses to Penetration, Avalanche, and Hot Key.
"Why isn't batch INSERT working?"
I know the trap where the IDENTITY strategy blocks bulk operations. ngăn chặn việc xử lý hàng loạt (bulk).
It's the same experience, but the answer determines whether you pass or fail.
- "p95 320ms→90ms, improved using cache."
- Answer with both the rationale for your choice and the alternatives considered.
- Even handles up to 7 patterns of follow-up questions.
I memorized the answers to the questions, so why do I keep failing?
Technical interviews look for the "why," not just the answer. Let's look at a common rejection flow.
Has this ever happened to you?
Have you ever been at a loss for words when asked, "Why did you use that technology?"
Have you ever answered, "It got a lot faster," and then regretted it?
A current developer who has interviewed at 24 companies will coach you directly.
A 6-year developer who reached the final interview stages at Coupang and Yanolja, and an instructor with a story of interviewing at 24 companies, will provide direct coaching.
Former Viva Republica (Toss) Server Developer — Covers strategies proven in actual interview settings.
Instead of just theory, we conduct live reviews of actual students' resumes and answers to provide immediate feedback.
We support students until the very end by operating a developer job search community (KakaoTalk, Discord).
3 days · 30+ lectures, from resume interviews to technical interviews.
Streamlining experiences → proving with metrics and concurrency → aligning with corporate DNA and caching. We will proceed by revising actual resumes live. Click on a section to view the detailed table of contents.
섹션 1. 📅 Day 1 · 경험의 흐름화 + DB 핵심 원리경험 질문
- 1👋 Welcome! Starting the 3-day interview survival guide
- 2👁️ Interviewers look at the 'why,' not the 'what'
- 3🌱 What if I'm a new recruit with no experience?
- 4📝 Creating a Story with a 5-Chapter Structure + Practical Resume Diagnosis
섹션 2. 📅 Day 2 · 수치로 증명하기 + 동시성 제어수치화·동시성
- 5💯 Interviewer's Confession: 90 Conceptual Candidates vs. 1 Practical Candidate
- 6📐 A-B-C Answer Formula: The Secret to Every Successful Answer
- 7🎤 7 Patterns of Follow-up Questions: The Truth About Freestyle
- 8📊 Practical Workbook: Before (0 points) → After (100 points) Transformation
- 9⚙️ Transaction Isolation Levels: Concurrency vs. Consistency
- 10🔒 Pessimistic vs Optimistic Locking: Learning Concurrency from Toilet Stalls
섹션 3. 📅 Day 3 · 기업 DNA + 캐싱·심화기업·캐싱
- 11🏢 Corporate DNA Dissection: Complete Mastery of Naver/Kakao/Coupang/Toss
- 12🛡️ 5 Survival Techniques for When You Don't Know: Silence is the Worst
- 13📋 4-Week Interview Prep Plan & Day-of Checklist
- 14💾 3 Caching Strategies: Why Cache Aside is King
- 15💥 3 Major Cache Failures: Penetration/Avalanche/Hot Key
- 16⚡ The Pitfall of JPA Bulk Operations: IDENTITY Prevents Batching
If you keep failing interviews but don't know why.
Who this is for
"I've used Redis"—those who only give abstract answers like this
Those who get stuck on follow-up questions ("Why did you choose this?", "Are there other ways?")
Those who have projects but cannot express them effectively for interviews
Those who know the technology but cannot provide the reasoning for "why they used it"
Those who need to align expectations
- Beginners who want to learn CS concepts step-by-step from the very beginning
- Those who are starting coding as non-majors or with zero base
- Those preparing for non-backend roles such as frontend or product planning
Beginner — You can start with just one project experience.
At least one backend project experience (school assignments, bootcamps, and toy projects are all acceptable).
Experience creating a simple API with Spring or Node.js.
Experience studying object-oriented programming, DB, cache, or index at least once..
By the end of the course, you will be able to do these four things.
Create a passing answer using the ABC answer formula of Problem → Solution → Improvement Metrics.
You will not be shaken by 7 patterns of follow-up questions such as "Why did you choose that?" or "Was there another way?"
Even for questions you don't know, respond with survival techniques that demonstrate your thought process instead of remaining silent.
You can prepare company-specific customized answers and follow-up questions for Naver, Kakao, Coupang, and Toss.
Leave a course review and receive a practical interview preparation template.
Interview strategy checklists by company, project catalogs, and experience & technical question libraries — this is a Notion template you can use for direct practice.
Expand and check only the parts you are curious about.
신입이라 경험이 별로 없는데 들어도 되나요?
Yes. Even a single toy project, bootcamp project, or school assignment is enough. We cover everything starting from "how to appeal yourself when you have no experience."
진짜 모르는 질문이 나오면 어떻게 하나요?
Silence is the worst. We will practice 5 survival techniques exactly as they are: sharing your thought process, buying time with clarifying questions, narrowing the scope (K8s→Docker), and honesty combined with a willingness to learn.
수치화할 경험이 없는데요?
I will provide a template on how to quantify results by measuring Before/After using K6 load testing, even for toy projects.
CS를 하나도 모르는 완전 입문자도 되나요?
This course is for beginners. It assumes you have completed at least one backend project and have experience studying object-oriented programming, databases, cache, and index at least once.
Don't just memorize; explain the 'why'.
Interviewers look for whether you can explain the reasons behind your choices, not whether you have memorized the answers. In just three days, abstract answers will transform into data-driven evidence, and you will remain unshaken even by follow-up questions.
Recommended for
these people
Who is this course right for?
A backend developer who has a technical interview scheduled but feels overwhelmed and unsure of where to start.
A junior developer who has experienced a mental breakdown after answering only "ACID..." to the question "What is a transaction?"
Junior developers who have completed projects but cannot answer with numbers when asked, "So, what were the results?"
Applicants who fail because they repeat the same answers in every interview
Need to know before starting?
Basic experience using Spring Boot
Basic experience using JPA
Hello
This is dingcodingco
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🚀 Former Toss, POSTECH graduate | Current Backend Developer (+9 years)
🎥 YouTuber with 20,000 subscribers | Development content creator
📚 Inflearn Instructor | Over 18,000+ cumulative students
👥 Managing a developer career community (8,000+ members)
🧩 Contributor to multiple open-source projects (Gradle, Spring AI, etc.)
📝 Passed 38 resume screenings & experienced in 100+ Kmong resume reviews (5.0 rating)
I deliver vivid, real-world industry insights in a way that is easy to understand and logically deductive.
Truyền tải những thông tin thực tế sống động từ ngành công nghiệp một cách dễ hiểu và có tính diễn dịch.
Curriculum
All
34 lectures ∙ (3hr 33min)
Course Materials:
Reviews
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81 reviews
5.0
81 reviews
bshookhu0978Reviews 1
∙
Average Rating 5.0
5
19% enrolledI paid four days before my interview. I'll complete the course and make sure to do well and share the good news of my acceptance! Thank you for the great lecture.
- dingcodingcoInstructor
Since this lecture is structured to quickly cover the key points even with a tight deadline of just four days, I believe it will suit you well. I truly hope you get great results!
jyjyReviews 1
∙
Average Rating 5.0
5
100% enrolledI was able to resolve the parts that felt overwhelming while preparing for a career move, and through the lectures, I realized which areas I was lacking in. Thank you for the great lecture!
- dingcodingcoInstructor
It is truly rewarding to hear that preparing for your career transition provided you with the opportunity to identify your own areas for improvement. I wish you the very best and hope for a successful outcome. Thank you!
jslReviews 6
∙
Average Rating 5.0
5
100% enrolledThis was very helpful. I've taken other interview lectures, but the answers to the interview questions in this course seem to be the best. I also feel like I gained a lot of trendy tips, so my satisfaction with the lecture is high.
- dingcodingcoInstructor
Thank you so much for comparing my course with others and giving it such a positive review. I'm glad to hear the trendy tips were helpful; it makes all the preparation feel worth it. I wish you the best of luck with your interview.
wjdgusxo998723Reviews 1
∙
Average Rating 5.0
Edited
5
32% enrolledI'm someone who failed 13 interviews in a row. While watching the interview lecture, I realized how lacking I am, even though I don't fully understand it yet😢 I'll work hard until I understand it.
- dingcodingcoInstructor
It is truly admirable that you continue to challenge yourself without giving up, even after the difficult experience of a 13-game losing streak. If you keep watching repeatedly, there will surely come a moment when everything connects, so please trust in that moment and see it through to the end.
- bettertomorrow
Reviews 2
∙
Average Rating 5.0
5
97% enrolledI was feeling overwhelmed with interview preparation, but after looking up your lecture, I feel like I've found the right direction. I will prepare well according to what you taught me and make sure to pass! Thank you.
- dingcodingcoInstructor
I am so glad to hear that you've found a sense of direction for your interview preparation, which must have felt overwhelming. I am sincerely rooting for you to prepare well and bring back the news of your success!
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