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Created 2026-09-15 · Updated 2026-10-12 · System Design
Algomi Blogs
System design, AI engineering, databases, networking, concurrency and more, written for engineers building real trading and fintech systems — part of the Algomi Suite.
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The Enterprise Architect's Interview Framework: From Business Problem to a Design You Can Defend
Start here if you are preparing for an Enterprise Solutions Architect interview: the ten-step framework, the landscape you design into, the four diagrams to draw, how to speak about trade-offs, and a worked example.
Created 2026-10-12 · Updated 2026-10-15 · System Design
System Design Made Simple
An original system design series — five foundation guides, fifteen focused case studies, and two deep dives — start here.
Created 2026-09-15 · Updated 2026-10-12 · System Design
System Design Starts with a Library, Not a Server
Follow one school library's reservation app from a single server to forty schools: requirements, estimation, scaling, storage choices, replication, consistency, CAP/PACELC, and the hashing tricks behind large-scale systems. Every idea arrives because a real problem forces it. Guide 1 of 5.
Created 2026-09-15 · Updated 2026-10-15 · System Design
What Happens Between a Click and an Answer?
Follow Riya's tap on 'Reserve' from her phone to the library's database and back: IP, DNS, HTTP, TCP/UDP, CDNs, load balancers, proxies, API styles and live updates, each introduced by the problem that forces it. Guide 2 of 5.
Created 2026-09-15 · Updated 2026-10-15 · System Design
Let Each Part Do Its Job: How One School Library App Grew Up
Follow one school library's reservation app from a single program to a system with a broker, outbox, saga and read model. Every pattern arrives because a real complaint forces it: monoliths vs microservices, async jobs, queues and streams, delivery guarantees, retries, outbox, sagas, CQRS, event sourcing, and the object patterns inside the code. Guide 3 of 5.
Created 2026-09-15 · Updated 2026-10-15 · System Design
A Good System Still Works on a Bad Day
Meera's library app has a very bad term: a dead server, a lost zone, a runaway retry storm, a deleted table and a stolen reservation. Each disaster introduces one idea: SLIs/SLOs, redundancy and failover, circuit breakers and rate limiting, authentication vs authorization, OAuth/OIDC, and recovery targets. Guide 4 of 5.
Created 2026-09-15 · Updated 2026-10-15 · System Design
Explain the Design, Then Defend the Decisions
Arjun, who built the library app in guides 1 to 4, sits a system design interview and is asked to design... a library reservation system. Follow his 45 minutes: scope, data, API, the last-copy race, lost responses, failures, growth, then two follow-up cases (async reports, a live feed), and the two-week plan he used to prepare. Guide 5 of 5.
Created 2026-09-15 · Updated 2026-10-15 · System Design
Hotel Reservations: How to Promise a Room Only Once
From one guesthouse in Goa to 80,000 hotels: how a booking system claims every night of a stay exactly once, keeps payment uncertainty away from inventory, and stops two guests winning the same room. Includes the three follow-up questions interviewers use to separate good answers from great ones.
Created 2026-09-16 · Updated 2026-10-15 · System Design
Airline Management: One Journey, Several Carefully Kept Promises
Follow Ananya and her father from Pune to Srinagar via Delhi, through a fog cancellation and an aircraft swap, to see how an airline system models dated flights, multi-leg bookings and disruptions as durable workflows instead of simple status edits.
Created 2026-09-16 · Updated 2026-10-15 · System Design
Inventory Management: Knowing What You Can Still Promise
Back-to-school season at an online stationery shop: why on-hand stock isn't available stock, how atomic reservations stop two orders claiming the same calculator, and how shipments, cancellations and warehouse transfers stay honest.
Created 2026-09-16 · Updated 2026-10-15 · System Design
ATM Design: When Software Must Agree with a Physical Machine
A monsoon power flicker hits a village ATM just as ₹10,000 slides out. How do you design a withdrawal that survives a network failure between the bank's authorization and the machine dispensing cash, when cash can never be rolled back?
Created 2026-09-16 · Updated 2026-10-15 · System Design
Designing Authentication: Proving Who You Are
A stolen laptop, a forgotten password and a 'Sign in with Google' button: follow one student's account to design registration, login, sessions, recovery, MFA and OIDC sign-in around durable identity instead of trusted client claims.
Created 2026-09-16 · Updated 2026-10-15 · System Design
Designing a CDN: Put Popular Content Near Its Readers
A national e-textbook platform, results day, and one leaked answer key: how a CDN serves popular content close to readers, why the cache key is a correctness decision, and how to stop a stampede from flattening the origin.
Created 2026-09-16 · Updated 2026-10-15 · System Design
Designing Photo Storage: From Small Files to a Large Photo Service
Sunita uploads 400 wedding photos from a train with patchy Wi-Fi. Follow them through a photo service that separates bytes from metadata, treats upload, processing and deletion as retryable workflows, and borrows one big idea from Facebook's Haystack.
Created 2026-09-16 · Updated 2026-10-15 · System Design
Designing a Job Scheduler: Remember the Work, Expect Retries
Every Monday at 08:00, 600 schools send progress reports to parents. One Monday some parents get two and some get none. Here is why a job definition, a scheduled run and an execution attempt must be three different records, and why leases don't erase duplicate effects.
Created 2026-09-16 · Updated 2026-10-15 · System Design
Designing a Professional Network: People, Connections, and Feeds
Follow Imran, a junior developer looking for his next job, through a LinkedIn-like network: how to model connections and follows, why search and feeds are projections, and how a hybrid fan-out keeps one famous post from flooding the system.
Created 2026-09-16 · Updated 2026-10-15 · System Design
Designing an Online Chess Game: Rules First, Servers Second
An inter-school blitz final between Chennai and Delhi tests everything: why the server must be the referee, why a board picture isn't the full state, and how one game stays correct through double taps, a ticking clock and a server failover.
Created 2026-09-16 · Updated 2026-10-15 · System Design
Designing BookMyShow: Selling Each Seat Only Once While Thousands Rush In
9:00 on a Friday, first-day-first-show bookings open for a superstar's film, and 100,000 fans want 400 seats. How a ticketing system holds seats for a few minutes, keeps payment uncertainty away from inventory, and stays fair when the crowd arrives.
Created 2026-09-26 · Updated 2026-10-15 · System Design
Designing YouTube: From One Upload to a Video Anyone Can Play
A 17-year-old uploads a 2 GB cooking video over a shaky connection. By evening it has a million views, including his grandmother's, on a 2G phone. Follow it to see how a video platform accepts huge uploads, builds many playable versions, serves them from nearby caches, and counts views without a slow database.
Created 2026-09-26 · Updated 2026-10-15 · System Design
Designing Netflix: Putting the Movie in a Box Near the Viewer
Friday, 9 pm: a hit series drops its new season and a family in Kochi presses play along with millions of others. How a streaming service keeps the cloud for decisions and puts the video bytes on cache appliances inside viewers' internet providers, stocked overnight before anyone asks.
Created 2026-09-26 · Updated 2026-10-15 · System Design
Designing Hotstar: Live Cricket for Tens of Millions at Once
World Cup final night: a student on a cheap phone in Bihar and a family on a big TV in Pune press play at the toss, along with tens of millions of others. How a live-sports platform survives a crowd that arrives all at once: a stream for every screen, caching what can be cached, scaling in steps before the toss, and switching off extras so the video keeps playing.
Created 2026-09-26 · Updated 2026-10-15 · System Design
Designing a Payment System: Charging a Customer Once, Even When Networks Fail
Mrs. Rao pays ₹1,000 for Diwali groceries, the network hiccups, and she taps Pay again. Follow her payment through idempotency keys, an honest 'unknown' state, webhooks, a double-entry ledger and daily reconciliation, then up to the enterprise questions: stakeholders, compliance, failover and how the design grows.
Created 2026-09-26 · Updated 2026-10-15 · System Design
Ultra-Resilient Architecture: Keeping a Service Useful When Parts Fail
Three zones don't help if they all depend on one shared database. Quorums, static stability, multi-region trade-offs, and why replication isn't a backup.
Created 2026-09-21 · Updated 2026-10-15 · System Design
gRPC in Depth: Calling Another Service Without Pretending the Network Is Reliable
Contracts, Protocol Buffers, HTTP/2 streams, deadlines, status codes, retries, load balancing, keepalive, and browsers: how gRPC works and where the sharp edges are.
Created 2026-09-26 · Updated 2026-10-15 · System Design
Algomi Architecture, Part 1: The Backbone Every Product Shares
How Algomi's five web apps, single login, stateless API, shared library, market-hours worker, and hand-applied database migrations fit together.
Created 2026-09-26 · Updated 2026-10-15 · System Design
Algomi Architecture, Part 2: Trading, Insights, Charts, Career, and the AI Guardrails
How a Telegram message becomes a broker order, why recommendations refuse to guess, and how one doorway keeps personal data away from third-party AI models.
Created 2026-09-26 · Updated 2026-10-15 · System Design
Interview Roadmap Appendix: 107 Topics, One Index
A study index for system design and AI system design interviews: every roadmap topic mapped to the post and section that teaches it, the HLD, LLD and AI interview frameworks, a ten-phase study order, and a readiness checklist with links.
Created 2026-09-29 · Updated 2026-10-02 · System Design
Inside a Database: Indexes, Transactions, and Storage Engines
What a database does between your query and the disk: ACID, isolation levels and their anomalies, B-tree and LSM storage engines, write-ahead logs, index design, query plans, connection pools, and how to choose between SQL and NoSQL.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Scaling Data: Replication, Sharding, and Distributed Transactions
When one database is not enough: replication topologies, choosing a shard key, hot partitions, global secondary indexes, and how to keep a business operation correct across services with 2PC, sagas, and the outbox pattern.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Consistency Models, Quorums, and Logical Clocks
What 'consistent' actually means: CAP and PACELC, the ladder from linearizable to eventual, quorum arithmetic, and how vector clocks and CRDTs let replicas agree without a shared clock.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Consensus, Raft, Distributed Locks, and Leader Election
How machines that can crash and messages that can vanish still agree on one answer: the Two Generals problem, Byzantine faults, Raft in plain language, leader election, split brain, and why a lock needs a fencing token.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Caching Deep Dive: Patterns, Invalidation, and Stampedes
Where to cache, which write pattern to use, how to evict, how to invalidate, and how to survive cache stampedes, penetration, and hot keys, with the trade-offs an interviewer expects you to name.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Load Balancing, Global Traffic, TLS, and HTTP Versions
Layer 4 versus layer 7 balancing, algorithms and health checks, DNS and anycast for global traffic, the TLS handshake, what changed between HTTP/1.1, 2 and 3, and where an API gateway fits.
Created 2026-09-29 · Updated 2026-10-15 · System Design
API Design: Pagination, Idempotency, Rate Limiting, and Access Control
REST, GraphQL and gRPC choices, cursor pagination, idempotency keys, versioning, a rate limiter designed end to end (token bucket, sliding window, distributed), and RBAC, ABAC and JWT trade-offs.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Kafka and Messaging Reliability: One Diwali Night in Ravi's Sorting Office
Follow one night in a busy sorting office to learn how Kafka stores and replicates messages, what acks and ISR really guarantee, delivery semantics, rebalancing, lag, poison pills, dead-letter queues, and retries with backoff and jitter.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Data Platforms: Batch, Streaming, CDC, and the Lakehouse
OLTP versus OLAP, batch versus stream, lambda and kappa, windowing and late data, change data capture, data lakes and warehouses, and how to keep a pipeline correct when events repeat or arrive late.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Search, Autocomplete, Web Crawling, Time-Series, and Ad-Click Aggregation
Inverted indexes and ranking, a typeahead service built on tries, a polite web crawler, time-series storage with downsampling, and exactly-once-ish ad-click aggregation.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Location-Based Services: Geohash, Quadtrees, Nearby Search, and Ride Matching
How to answer 'what is near me?' at scale: geohash, quadtrees, S2 and H3 cells, a proximity service, and a ride-hailing dispatcher that ingests millions of moving driver locations.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Collaborative Editing: Operational Transformation, CRDTs, and Presence
How two people type in the same document at once without losing each other's words: operational transformation, CRDTs, the server architecture around them, presence, offline editing, and version history.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Stock Exchange and Broker Design: Order Books, Matching Engines, and Risk
How an exchange matches buyers and sellers deterministically: the limit order book, price-time priority, a single-threaded sequenced matching engine, market data fan-out, and the broker's order gateway and pre-trade risk checks.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Chat and Notification Systems: Real-Time Delivery at Scale
Designing a WhatsApp-style chat (connections, message flow, ordering, delivery receipts, offline sync, group fan-out) and a notification platform (channels, templates, preferences, retries, deduplication).
Created 2026-09-29 · Updated 2026-10-15 · System Design
News Feed and Social Graph: Fan-Out, Ranking, and the Celebrity Problem
Fan-out on write versus on read, the hybrid that tames celebrity accounts, storing the follow graph, feed ranking, counters, and pagination for a timeline that must feel instant.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Storage Case Studies: URL Shortener, Key-Value Store, and File Sync
Three classic designs worked end to end: a URL shortener (ID generation, redirects, analytics), a Dynamo-style distributed key-value store, and a Dropbox-style file sync service with chunking and deduplication.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Capacity Estimation and Load Testing: Back-of-the-Envelope Done Properly
The numbers every engineer should know, a repeatable method for QPS, storage, bandwidth, and server counts, worked examples, and how to check the estimate with load tests and percentile latency.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Production Engineering: Observability, Security, Deployment, Kubernetes, and Cost
What separates a design on paper from a system you can run: metrics, logs and traces, SLOs, zero-trust security, safe deployment strategies, Kubernetes essentials, multi-region cloud choices, and cost control.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Low-Level Design Foundations: OOP, SOLID, and Design Patterns in Java, Told Through a Tea Shop
The object-oriented vocabulary and the handful of design patterns that machine-coding rounds actually use, explained like you are five through one tea shop, then shown in short runnable Java.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Concurrency and Multithreading in Java for LLD: Races, Locks, and Producer-Consumer
One busy restaurant kitchen explains race conditions, locks, deadlock, producer-consumer, thread pools, and thread-safe class design, with runnable Java 17 code and the Java-specific facts (memory model, volatile, ReentrantLock, ConcurrentHashMap, virtual threads) interviewers probe.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Machine Coding Case Studies, Part 1: Parking Lot, LRU Cache, Rate Limiter, Vending Machine (Java, via a Shopping Mall)
Four classic machine-coding rounds solved in modern Java through one neighbourhood shopping mall: the basement parking lot, the front-shelf LRU cache, the food-court token bucket, and the snack vending machine, each with design reasoning and follow-ups.
Created 2026-09-29 · Updated 2026-10-15 · System Design
Machine Coding Case Studies in Java, Part 2: A Weekend Hotel Trip with Splitwise, Elevator, Tic-Tac-Toe, Logger, and Design Sketches
One weekend hotel trip, told in modern Java: expense sharing with debt simplification, a lift scheduler, tic-tac-toe with O(1) win checks, a pluggable trip diary (logger), plus class sketches for seat booking, notifications, a library, cab dispatch, food delivery, and chess.
Created 2026-09-29 · Updated 2026-10-15 · System Design
ML System Design and Recommendation Systems: From Data to Ranking in Production
The end-to-end shape of a production ML system (framing, data, features, training, serving, monitoring) and the two-stage recommender pattern with candidate retrieval, ranking, metrics like NDCG, and cold start.
Created 2026-09-29 · Updated 2026-10-15 · System Design
How Kafka Log Compaction Keeps Only the Latest Value per Key (and Where It Bites You)
What log compaction actually does inside a Kafka broker: dirty and clean sections, the cleaner's offset map, tombstones and delete.retention.ms, the settings that decide when a record really disappears, and the three interview questions that trip people up.
Created 2026-10-15 · Updated 2026-10-15 · System Design
API Monitoring: Proving the Library Can Still Reserve a Book
A health check that passes while nobody can reserve a book: how to monitor API outcomes with synthetic journeys and real-request telemetry, keep test traffic safe, turn failures into actionable alerts, and defend the cost, privacy and recovery decisions in an interview.
Created 2026-10-17 · Updated 2026-10-17 · System Design