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System Design and AI Engineering, by Roni Das. 980 interactive lessons.
Start LearningSDE-2 (Software Development Engineer II) is the level after entry level at Amazon, and many other companies use the same name for a mid-level engineer. At this level the loop usually adds a system design round: you are given a product such as a URL shortener or a notification service, and in about an hour you design it end to end. Amazon's own SDE II prep page says: "Expect at least one question on software systems design." The bar is a complete, working design with sensible numbers and one solid deep dive, not every trade-off a senior engineer would cover.
Preparing for an SDE-2 loop? The System Design course teaches every building block this round uses, from caching and queues to sharding, and ends with full designs of the classic problems.
At entry level (SDE-1), most rounds are coding. At SDE-2 the company expects you to own a feature or a small service, so it checks whether you can design one. The question is usually a well-known product. What is graded is how you get there: asking the right questions, sizing the load, choosing parts for a reason, and explaining what breaks.
Our view of the levels, which is how we teach them: an SDE-1 answer often stops at boxes. An SDE-2 answer is one complete design that would work, with numbers, a data model and one deep dive. A senior answer adds many failure modes, cost, migration and the trade-offs between several designs. Companies set their own bar, so treat this as a guide, not a rule.
Backend engineers have an advantage here: you already know APIs, databases and queues from work. The gap is usually saying it out loud in order, and doing the numbers quickly.
“Expect at least one question on software systems design.”
“At Amazon, designing software systems is unique due to our size and speed of change.”
“The most important thing a SDE does at Amazon is write scalable, robust, and well-tested code.”
“Each interviewer will typically ask two or three behavioral-based questions about successes or challenges.”
Quotes copied from the pages linked, read on 23 October 2026.
Ask what the system must do and what it must not do. Write down two or three features, plus the non-functional needs: how many users, how fast, how reliable.
Turn users into requests per second and storage per year. Rough is fine: the point is to see if one database is enough or if you need to split the data. Our free capacity estimator shows the steps.
Name the tables or documents, the main keys and the main query. Then pick SQL or NoSQL for a reason you can say in one sentence.
Know where a cache helps and how it goes stale, and when to move slow work to a queue so the user does not wait for it.
Read replicas for many reads, sharding when one machine cannot hold the writes, and a load balancer in front of stateless servers.
Pick the hardest part, such as duplicates on retry or a hot key, and explain the fix step by step. Amazon lists reliability, scalability and efficiency among the things its design questions look at.
For a backend engineer with a full-time job: about 8 to 10 hours a week, a rough guide and not a promise. Go faster where you already know the topic. Free lessons are marked; the rest are in the System Design course.
Days 1 to 30
Every design question is built from the same few parts. If you know each one well, the round becomes putting parts together, not inventing.
Prove it: Estimate the requests per second and storage for a URL shortener in five minutes, out loud, without notes.
Days 31 to 60
The deep dive is where SDE-2 candidates pass or fail. It is almost always about queues, duplicates, consistency or overload.
Prove it: Explain, with a drawing, how a payment request stays safe when the client retries after a timeout.
Days 61 to 90
Now you practise the round itself: the same problems come up again and again, and timing matters as much as knowledge.
Prove it: Do two full mock rounds with a timer and write down the two things you would change in each.
Most companies do not publish their loop. Amazon does, for SDE II, so here it is as Amazon wrote it. Other companies usually mix the same parts: coding, one design round, and a behavioural round.
Online assessment
"You'll have 90 minutes to complete two technical questions followed by 20 minutes of Systems Design scenarios."
The loop
"Your loop will include four 55-minute interviews where you'll meet with members of our software development community."
System design
At least one design question. Amazon says you "should ask questions to complete and validate your design".
Leadership Principles
"A significant portion of the conversation will focus on how you've demonstrated our Leadership Principles in your past jobs."
Here is the shape of a good answer to a classic prompt. The numbers are assumptions you say out loud, then use.
Design a notification service for a shopping app: order updates by email, SMS and push.
One worked answer is not enough for the loop.
Each question has why it is asked, a full answer, what the interviewer listens for, the follow-ups, the common mistakes and a diagram (268 diagrams in all). A PDF you keep, junior to staff level.
India: UPI, cards or netbanking through Razorpay. Elsewhere: card or PayPal. Download at once from My packs.
The System Design course has 770 lessons, and 18 of them are free to read first, with no card needed. It starts from latency and caching, goes through queues, replication and sharding, and ends with full designs of the classic interview problems. One payment, lifetime access.
Free 15-min Interview Readiness Check
A short call. I tell you the 2 or 3 things to fix first for your target role. It costs nothing, and it is booked on Topmate.
Also useful: System design roadmap, System design interview questions, 30-day plan, Low-level design guides and Forward deployed engineer guide.
