System Design (High-Level Design)
System Design (High-Level Design) interview questions
System design interview questions module by module, from caching, replication and messaging to building blocks and case studies, at every level.
A system design round hands you a loosely stated product and about 45 minutes. The interviewer watches how you turn it into requirements, rough numbers and a first design, and then pushes on the parts that break: a hot key, a lost message, a region that goes dark, a bill that grows faster than the traffic. Most of the signal comes from that second half, from how you reason when the first design meets a constraint it did not plan for.
The banks below follow the modules of this track. Each question names the levels it is asked at, what it tests and the first step of a good answer, with the follow-ups an interviewer is likely to add. Questions for freshers and mid-level engineers check that the building blocks are understood with numbers; senior questions add failure, trade-offs and operations; staff questions add ownership, migration and cost across teams.
Practise them the way the round works. Say the first step aloud, give yourself two minutes per follow-up, and write down the numbers you assumed before you compare notes. A question that changes one constraint, ten times the load, a second region or a stricter privacy rule, is worth repeating a week later: the second attempt is usually the one that shows judgement.
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Module 1
Start here: how system design works
18 questions: 6 warm-ups and 12 with model answers · Levels: Fresher to staff
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Module 2
Back-of-the-envelope estimation
18 questions: 6 warm-ups and 12 with model answers · Levels: Fresher to senior
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Module 3
Performance and reliability fundamentals
Percentiles and tail latency, availability arithmetic, error budgets, and the defences that stop one slow dependency from taking a service down with it.
30 questions: 10 warm-ups and 20 with model answers · Levels: Fresher to staff
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Module 4
Networking for system designers
What happens between a click and a response, from DNS and anycast through HTTP versions, proxies and gateways to load balancing and caching at the edge.
18 questions: 6 warm-ups and 12 with model answers · Levels: Fresher to staff
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Module 5
APIs and communication patterns
Choosing an API style and its HTTP semantics, calls that wait against calls that do not, real-time delivery, versioning, service identity, idempotency keys, paging and webhooks.
25 questions: 5 warm-ups and 20 with model answers · Levels: Fresher to staff
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Module 6
Data modelling and storage engines
Picking a data model, how indexes and storage engines work, isolation levels and concurrency control, relational against document stores, schema changes and analytical storage.
27 questions: 4 warm-ups and 23 with model answers · Levels: Fresher to staff
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Module 7
Caching
Where caches sit and how they fill, eviction and sizing with numbers, invalidation races, stampedes and hot keys, and the headers that decide what a browser or CDN may keep.
22 questions: 5 warm-ups and 17 with model answers · Levels: Fresher to staff
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Module 8
Replication
Leaders and followers, failover without split brain, the replication lag a user can notice, conflicts between several leaders and quorum reads and writes.
17 questions: 3 warm-ups and 14 with model answers · Levels: Fresher to staff
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Module 9
Partitioning and sharding
Spreading data across nodes by range or by hash, consistent and rendezvous hashing, and the keys that turn one partition into a hotspot.
21 questions: 4 warm-ups and 17 with model answers · Levels: Fresher to staff
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Module 10
Consistency, time and coordination
Consistency models, CAP and PACELC in practice, clocks and ordering, consensus, leader election with leases and fencing tokens, and when a distributed lock is safe.
23 questions: 6 warm-ups and 17 with model answers · Levels: Fresher to staff
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Module 11
Distributed transactions and workflows
Dual writes and two-phase commit, sagas and their compensations, the outbox pattern with change data capture, what exactly-once can mean and durable workflows.
19 questions: 5 warm-ups and 14 with model answers · Levels: Fresher to staff
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Module 12
Messaging and stream processing
Queues, logs and pub-sub, delivery guarantees and dead-letter queues, ordering within consumer groups, growing backlogs, stream processing and batch pipelines.
22 questions: 5 warm-ups and 17 with model answers · Levels: Fresher to staff
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Module 13
Architecture styles at scale
Monolith or microservices, discovery and service meshes, serverless and edge code, event-driven designs with CQRS, cells that limit the blast radius and migrating a live system.
22 questions: 5 warm-ups and 17 with model answers · Levels: Fresher to staff
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Module 14
Search, geospatial and probabilistic data structures
Inverted indexes and ranking, geospatial indexes, Bloom and cuckoo filters, typeahead, counting sketches, search in Indian languages and nearest-neighbour vector search.
25 questions: 5 warm-ups and 20 with model answers · Levels: Fresher to staff
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Module 15
Files, objects and media
Block, file and object storage, durability through erasure coding, resumable uploads, chunking and deduplication, media pipelines with adaptive bitrate and live video.
20 questions: 6 warm-ups and 14 with model answers · Levels: Fresher to staff
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Module 16
Observability, incidents and lessons from outages
Logs, metrics and traces, alerting on service levels, running an incident, load tests and capacity plans, and the retry storms and control-plane failures behind real outages.
22 questions: 5 warm-ups and 17 with model answers · Levels: Fresher to staff
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Module 17
Security, privacy and compliance
Threat modelling a design, keys and secrets, bots and denial of service, isolation between tenants, privacy by design under India's data protection law and audit trails.
20 questions: 3 warm-ups and 17 with model answers · Levels: Fresher to staff
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Module 18
Delivery, multi-region, disaster recovery and cost
Releases behind feature flags, migrations without downtime, designs that span regions, backups and disaster recovery, and a bill that grows no faster than the traffic.
21 questions: 6 warm-ups and 15 with model answers · Levels: Fresher to staff
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Module 19
Building blocks: traffic, storage and messaging
The parts other systems stand on, designed one by one, from unique IDs and a distributed cache to a message log, a key-value store, object storage and the traffic layer in front.
41 questions: 9 warm-ups and 32 with model answers · Levels: Fresher to staff
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Module 20
Building blocks: control, safety and platform services
Rate limiters, job schedulers, lock services, notifications, configuration and feature flags, sharded counters and a gateway in front of language models.
35 questions: 3 warm-ups and 32 with model answers · Levels: Fresher to staff
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Module 21
Recurring problems and the moves that solve them
The problems most designs meet sooner or later, from long-lived connections and long-running work to reconciliation, scaling reads and writes, contention, fan-out and sudden spikes.
29 questions: 5 warm-ups and 24 with model answers · Levels: Fresher to staff
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Module 22
Case studies: links, files and media
Designing a URL shortener, a paste service, music and video streaming, file sync, photo sharing, live cricket streaming and a video upload pipeline.
32 questions: 9 warm-ups and 23 with model answers · Levels: Fresher to staff
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Module 23
Case studies: social, feeds and search
Designing news feeds and timelines, a web crawler, trending topics, search autocomplete, web search, a news aggregator, a question-and-answer forum and dating matches.
33 questions: 7 warm-ups and 26 with model answers · Levels: Fresher to staff
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Module 24
Case studies: messaging, real time and collaboration
Designing one-to-one and group chat with end-to-end encryption, team chat, live comments, video calls, online chess and a collaborative editor.
31 questions: 5 warm-ups and 26 with model answers · Levels: Fresher to staff
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Module 25
Case studies: location, mobility and logistics
Designing ride-hailing matching and trips, proximity search and food delivery, where location updates arrive faster than any single database can store them.
23 questions: 3 warm-ups and 20 with model answers · Levels: Fresher to staff
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Module 26
Case studies: booking, commerce and contention
Designing seat booking, Tatkal-style booking bursts, an online checkout and a flash sale, where many buyers want the same few items in the same second.
26 questions: 3 warm-ups and 23 with model answers · Levels: Fresher to staff
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Module 27
Case studies: payments, money and markets
Designing UPI payment flows and their reconciliation, a payment gateway and a digital wallet, where every rupee has to be accounted for exactly once.
14 questions: 2 warm-ups and 12 with model answers · Levels: Fresher to staff
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Module 28
Case studies: India's digital public infrastructure
Designing an open commerce network, identity verification and an e-invoicing network in the style of India's digital public infrastructure.
16 questions: 4 warm-ups and 12 with model answers · Levels: Fresher to staff
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Module 29
Case studies: platforms, analytics and developer tools
Designing a real-time leaderboard, an online judge, analytics that respect privacy, ad-click aggregation, a CI/CD system and a shared calendar.
16 questions: 5 warm-ups and 11 with model answers · Levels: Fresher to staff
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Module 30
Interview practice and study plans
How design rounds are judged, running a self-mock against the clock, handling follow-ups and curveballs, and study plans for the weeks before an interview.
15 questions: 5 warm-ups and 10 with model answers · Levels: Fresher to staff