Modular Interview Questions (2026)
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Modular Monolith: Domain driven design, need help.
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I am building a SaaS with various business domains through modular monolith (microservice through code constraints rather than infrastructure constraints).
Example modules that users can subscribe to are Human Resources (HR), or Customer Resource Management (CRM). Below are initially how I would design it.
Public API Layer * Entirely entity based. * CRUD for employee entity, product entity, etc. * Not sure how I can scope a public API to a specific domain. * I will be using GraphQL for all CRUD operations * Auth endpoints will be using REST.
Service Layer * Domain model based on modules, HR and CRM. HR has specific entity like employee. * There will be many entities that need to be shared through various domains, like product. * Does product need to be its own service? Its odd then to have services based on entities and some based on domain. * I have other domains like billing that aren't an actual module that a user can subscribe to. Ex: Billing is part of every user. * Will I need a utils service domain for data managed solely by the SaaS and not users? Ex: list of countries, what modules are available (HR, CRM), what application settings are available. * Am I overcomplicating this? Just do everything based on an entity and call it a day. One entity = one service.
Data Layer * Using PostgreSQL. * I do not see much info on data modeling in terms of modular monolith. * I am thinking single database because it is still a monolith, but model it as a microservice. * Where I would normally have FK, I don't have them. I really can't seem to conceptualize this. I have an orders service. An order can have many products. But products is its own service. Adding a FK between orders table and products table is how I would it in traditional monolith. But now on the database layer, the orders table and products are technically tightly coupled. * Another problem I had, was dealing with supertype/subtype that span different domains. So the whole domain modeling wouldn't work well. * A customer and employee are actually the same entity. That entity is a party. Customer and employee are subtytpes. Party is supertype. But customer is within CRM domain and employee is within HR domain. The goal is do encapsulation well through code constraints, so when you actually have to do microservices through infrastructure it becomes a seamless transition. I just need advice on generally how to handle domain modeling with modular monolith at each layer.
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Modular Interview Process Overview
The Modular interview process typically includes a recruiter screen, one to two technical phone screens, and a 4-6 round on-site or virtual on-site loop. Each round serves a distinct calibration purpose: coding rounds measure correctness, code quality, and complexity reasoning; system design rounds measure architectural judgment at the appropriate level; behavioral rounds measure ownership, leadership scope, and collaboration. Reports tagged on LeakCode from 2024-2026 show Modular runs a calibrated process consistent with industry norms for companies of its tier.
Difficulty calibration: Modular coding rounds typically run medium difficulty with follow-up depth as the senior discriminator. System design rounds expect production-grade trade-off articulation at L4+ levels. Behavioral rounds expect quantified outcomes ("reduced p99 latency from 800ms to 120ms") rather than vague impact claims. The candidates who advance consistently demonstrate clear thinking out loud rather than perfect final answers.
How To Use Modular Question Reports
Real candidate-reported interview questions are a calibration tool, not a memorization target. Modular updates its question pool every 2-4 months; memorizing exact problems risks misleading you when the interviewer uses a variant. The high-leverage approach: identify the patterns that appear repeatedly in Modular reports, practice those patterns on similar (not identical) problems, and use the reports to understand the interviewer's typical follow-up depth.
Filter the questions above by round type, difficulty, and recency. Focus first on reports from the past 6-12 months; older reports may reference questions that have since rotated out of Modular's pool. Reports tagged with quantified difficulty and explicit round type are higher-signal than reports without those tags. The metadata filters help you build a focused study plan in 1-2 hours rather than 8-10 hours of unstructured browsing.
Common Modular Interview Mistakes
Reports tagged "no hire" at Modular consistently surface a few patterns: jumping into code without clarifying requirements, coding silently for extended periods, missing edge cases (empty input, single element, large input, overflow), producing working code the candidate cannot refactor when probed, and behavioral stories that use "we" instead of "I" diluting individual signal. Strong candidates explicitly avoid these patterns by following a consistent round template.
The single most predictive failure mode in recent reports: not asking clarifying questions. Interviewers are explicitly trained to weight this dimension. Strong candidates ask 3-5 clarifying questions even on problems that look obvious; weak candidates dive into implementation immediately. Strong candidates also verbalize their approach before writing code; weak candidates code in silence and lose the communication dimension of the round's calibration.