Backend Engineer Job Simulation
Ledgerline's payouts endpoint is slow, its Node process locks up, and Postgres keeps running out of connections. Four symptoms, four different causes. Find them, then design the webhook that handles real money without paying a merchant twice.
Join 100,000+ One Roadmap-certified candidates
Tom BradleyBackend Lead, Ledgerline
Welcome to Ledgerline. I'm Tom, Backend Lead. We move payouts for about 4,000 merchants, which means two things: our Node services have to stay up, and our database has to be right about money. Your first ticket is an incident - one endpoint with four separate failures, and I want to know which line causes which. Your second is a design review for a bank webhook where a duplicate would credit a merchant twice. I care much more about whether you can keep four problems distinct than about how fast you type.
Your manager for this simulation. Reviews feel this real too.
Why finish this simulation
A risk-free way to experience the backend job before you're hired - debug a real Node service under incident conditions, design a money-handling endpoint, and back your applications with evidence instead of a list of technologies.
Node and SQL, measured separately. Your answers map onto the Backend Engineer competencies in your Talent Graph - server-side programming, database knowledge, reliability and system design - so employers see which of them you actually demonstrated.
The incident, not the tutorial. Four symptoms with four different causes in one 40-line handler. Keeping them apart is the skill nobody tests for and every on-call rotation needs.
Event-loop intuition you keep. Once you have seen a single pbkdf2Sync take down health checks, you will never review a synchronous call in a request handler the same way.
Query plans, not query guesses. You will read an EXPLAIN, see 2.4 million rows discarded to return 300, and pick the index that fixes both the filter and the sort.
Idempotency that actually holds. BE-102 turns on one detail: whether your design survives two Node instances processing the same retry at the same moment. Most candidate designs do not.
Feedback that names the gap. Every submission returns per-question results and a rubric read of your notes, so a retry is targeted rather than a guess.
How it works
01Pick up a ticket
Real tasks land on your board like a Jira queue. Download the dataset and work in your tool of choice.
02Submit for review
Your work enters review - results within 24 hours (usually much sooner). The clock pauses while you wait, like a real take-home.
03Pass, then progress
Pass to unlock the next ticket. Clear every ticket to earn a certificate and a spot on the weekly leaderboard.
Skills you will learn and practice
- Why a *Sync call freezes an entire Node process
- Spotting a floating promise behind UnhandledPromiseRejection
- Reading EXPLAIN output: seq scan vs index scan
- Choosing the index a WHERE plus ORDER BY actually needs
- Recognising and fixing N+1 queries
- Connection pooling and why Client-per-request exhausts Postgres
- Database-enforced idempotency for webhook retries
- Transaction boundaries around a third-party call
The tickets
What you'll learn
- Why one synchronous call can stall an entire Node process, health checks included
- How to read EXPLAIN output and pick the index a filter plus sort actually needs
- What a floating promise is, and why it surfaces hours later as an unhandled rejection
What you'll do
- Read a real Express handler, a Postgres schema and a slow-query plan
- Attribute four distinct production symptoms to four distinct lines
- Write the fix note your lead reads before approving the PR
Weekly leaderboard
Highest ranking points top the board - your score counts 80%, your speed 20%.
Your Future Certificate
Preview only. Clear both tickets to earn your personalized certificate - free.
Verified Certificate
Unique verification URL & QR code
LinkedIn Integration
Add to your profile with one click
Performance Analysis
Detailed insights into your results
Issued by DPIIT-recognized & MSME-registered company
Clear it, prove it
Pass both tickets and your verifiable certificate is free - add it to LinkedIn right away. Want to go deeper? Generate a personalized AI review of your performance for a one-time ₹99.