All 110 articles, sorted alphabetically
System Design: Rate Limiting
A comprehensive guide to rate limiting: token bucket mechanics, distributed Redis-backed implementations, sliding window and leaky bucket algorithms, …
Read article →System Design: Load Balancing - AICassindra
Deep dive into load balancing: algorithms (round-robin, least connections, IP hash, consistent hashing), L4 vs L7 decisions, health checks, session st…
Read article →Airbnb Smart Pricing Architecture
The ML system that suggests nightly prices to millions of Airbnb hosts. Covers feature extraction from location and history, demand modeling with tree…
Read article →Alipay Super-App Architecture, in depth: LDC unitization, RZone, GZone and CZone, cross-unit payments and unit-level failover
How Alipay scales by unitization: why sharding alone is not enough, the LDC zone model with RZones, a single GZone and per-city CZone mirrors, routing…
Read article →Amazon Shopping Cart Architecture, in depth: the always-writable cart, replication and merge semantics, guest carts, price revalidation and the checkout handoff
How to design an Amazon-scale shopping cart from first principles: why the cart must accept writes during failures, what the public Dynamo paper says …
Read article →API Versioning Strategies, in depth: carriers, major versus dated versions, and serving every version from one codebase
How to run many API versions at once without forking your code: what a version protects, URL, header, media type and account-pin carriers, major versu…
Read article →ATM End-to-End Architecture, in depth: terminal, PIN security, ISO 8583 authorization, reversals and the cash you cannot un-dispense
How an ATM cash withdrawal works end to end: the terminal device layer, PIN blocks and key hierarchy with HSM translation, ISO 8583 financial and reve…
Read article →Autocomplete / Typeahead Architecture, in depth: top-k tries, decayed popularity, trending deltas and the per-keystroke latency budget
How to build a search typeahead that answers every keystroke in tens of milliseconds: requirements and sizing, a trie that caches the top-k completion…
Read article →Cache Invalidation Strategies, in depth: Staleness Budgets, CDC Pipelines and Purges
Cache invalidation as a delivery system: staleness budgets, strategy comparison, a CDC-driven invalidator with code, generation counters and CDN tag p…
Read article →CQRS + Event Sourcing Architecture, in depth: building it on PostgreSQL
Building CQRS with event sourcing on one PostgreSQL database: the events table and optimistic concurrency, command handlers, the commit-order gap that…
Read article →Credit Card Payment Flow Architecture, in depth: the four-party model, authorisation, clearing and settlement, tokens and 3-D Secure, and a merchant service that survives timeouts
How a card payment really flows: issuer, acquirer, network and PSP roles, ISO 8583 authorisation and holds, capture, clearing, settlement and intercha…
Read article →Database Sharding Architecture, in depth: the shard map, the routing tier and live resharding
The machinery around a sharded database: mapping keys to keyspace ids and shards, where the router lives, versioned shard maps and stale-route protect…
Read article →Designing a Real-Time Chat System (1M concurrent users)
End-to-end architecture for a WhatsApp-scale chat system, from connection layer to message storage.
Read article →Designing an Event-Driven Order System, in depth: state machine, event contracts, reservations, payments and failure walk-throughs
An end-to-end design for an event-driven e-commerce order system: the order state machine, event envelopes, per-order ordering by key, inventory reser…
Read article →Designing a Feature Flag System, in depth: requirements, data model, evaluation semantics, propagation and failure modes
A system design walk-through of a feature flag platform: requirements and capacity estimates, the flag data model and versioning, a precise evaluation…
Read article →Designing a File Upload Service (S3-style)
Designing an upload service: control plane versus data plane, multipart and resumable uploads, integrity checks, content-addressed dedup, and lifecycl…
Read article →Designing a Metrics Aggregation System
Designing a metrics platform: series cardinality, push versus pull ingest, sharding by series, the TSDB write path, rollups, and per-tenant limits.
Read article →Designing a Payment System, in depth: a marketplace pay-in and pay-out design from requirements to reconciliation
An end-to-end payment system design for a marketplace: requirements and capacity, the data model, a guarded payment state machine, safe PSP calls, pay…
Read article →Designing a Quota System, in depth: allocation, rate and budget quotas, tenant hierarchies, leases and reconciliation
How to design a multi-tenant quota system: the difference between rate limits and quotas, the tenant hierarchy and data model, transactional reservati…
Read article →Designing Search at Scale, in depth: sizing shards and replicas, taming fan-out tail latency, fresh indexing and zero-downtime reindexing
How to take a search system from one cluster to production scale: the three independent scale axes, sizing shards from measured bytes per document, si…
Read article →Designing Uber Dispatch System
Ride dispatch as an assignment problem: location ingestion, supply indexing, batched matching, offer state machines, idempotent dispatch and regional …
Read article →Directory-Based Sharding, in depth: entry granularity, the directory data model, cached resolution with epochs, moving one tenant and isolating hot tenants
Directory-based sharding from first principles: how it compares with hash and range sharding, choosing per-key, per-tenant or virtual-bucket entries, …
Read article →Discord Architecture, in depth: the gateway, Elixir guild processes, ScyllaDB message storage and the voice SFU
How Discord delivers real-time text and voice at scale: the gateway WebSocket protocol and sharding, Elixir session and guild processes and their fan-…
Read article →DoorDash Architecture, in depth: from a Django monolith to Kotlin services, Cadence fallbacks and DeepRed dispatch
DoorDash food delivery architecture: what DoorDash published about its Python monolith to Kotlin gRPC migration, the checkout service on Cassandra, Ka…
Read article →Dropbox File Sync Architecture, in depth: block hashing, the journal and cursors, the three-tree client and conflict handling
How a Dropbox-style file sync system works end to end: splitting files into 4 MiB blocks with SHA-256 content hashes, committing metadata only after b…
Read article →Elasticsearch Cluster Architecture, in depth: node roles, master election and voting, cluster state, shard allocation, replication and recovery
How an Elasticsearch cluster is built and kept consistent: node roles and topology, discovery and the voting configuration, cluster-state publication,…
Read article →Email Delivery Architecture, in depth: SMTP relay, SPF, DKIM and DMARC alignment, retry queues, bounces, and staying out of the spam folder
How a production email sending system works end to end: submission and relay over SMTP, envelope versus header sender, SPF, DKIM and DMARC with alignm…
Read article →Event-Driven Microservices Architecture, in depth
Event-driven microservices architecture at estate scale: a reference architecture, topic ownership and naming, CloudEvents envelopes and schema compat…
Read article →Facebook Messenger Architecture, in depth: Iris ordered queues, snapshot-plus-delta sync over MQTT, the MyRocks migration and what default encryption changed
How Facebook Messenger is built, from Meta's own engineering accounts: Iris as an ordered update queue with per-consumer pointers and storage tie…
Read article →Real-Time Fraud Detection System Architecture, in depth: the synchronous decision path, streaming features, rules plus models, delayed labels and failing safely
How to design a real-time fraud detection system for payments: the authorisation-time decision path and its latency budget, online features in three f…
Read article →Geo-Partitioning, in depth: data residency, home-region keys, cells versus row-level placement, leak audits and re-homing
Geo-partitioning for data residency explained: residency versus latency, choosing the home-region key, region cells versus row-level placement, Cockro…
Read article →Google Drive + Docs Real-Time Collaboration Architecture, in depth: the ordering point, the op log, sessions, permissions and offline edits
A first-principles reference architecture for Google Docs-style real-time collaboration on top of a Drive-style file service: central-server operation…
Read article →Google Maps Real-Time Traffic Architecture, in depth: probe ingestion, map matching, segment speeds, supersegment ETA models and live routing
How a real-time traffic system like Google Maps turns anonymous phone location into segment speeds, live route weights and ETAs: probe ingestion and p…
Read article →Google Search Architecture, in depth: crawling, rendering, incremental indexing, sharded serving, tail latency and the ranking cascade
What Google has actually published about its search architecture: crawl budget and politeness, deferred rendering, Percolator's incremental index…
Read article →Grab Architecture, in depth: shared platforms for rides, food and payments, geohash location, ETA-based allocation, food batching and the wallet ledger
How a Southeast Asian super app like Grab is structured: vertical services over shared identity, location, allocation, pricing and payments; geohash l…
Read article →GraphQL Architecture, in depth: execution, batching, cost limits, persisted queries and federation
How a GraphQL server really works: parse, validate and execute, null propagation, N+1 and DataLoader batching, static query cost limits, trusted docum…
Read article →gRPC + Protobuf Architecture, in depth: the contract layer, wire encoding by hand, presence, breaking-change checks, field masks, rich errors and codegen
The Protobuf contract layer of a gRPC system: a message encoded byte by byte, field presence, compatibility rules enforced in CI with buf, package ver…
Read article →Hash Sharding, in depth
Hash sharding in depth: choosing a stable hash, why hash mod N moves most data on resize, fixed logical slots and slot maps, jump consistent hash, sha…
Read article →iCloud Sync Architecture, in depth: CloudKit zones, change tokens, conflicts and CKSyncEngine
How app data syncs through iCloud with CloudKit: containers, databases and record zones, delta sync with change tokens, silent push, optimistic concur…
Read article →iMessage Architecture, in depth: the IDS key directory, APNs delivery, per-device fan-out, PQ3 and attachments
How Apple's iMessage is structured, from Apple's published security documentation: device registration with the identity directory, per-devi…
Read article →Instagram Feed Generation Architecture, in depth: per-surface ranking, blending followed, suggested and ad content, and stable media-heavy pages
A reference architecture for an Instagram-style feed: separate pipelines per surface, unseen followed inventory with an adaptive lookback, suggested a…
Read article →Kafka Partition Architecture, in depth: segments and indexes on disk, high watermarks, replica placement, sizing partition counts and reassignment
What a Kafka partition physically is and how to design around it: segment, offset-index and time-index files, retention and compaction per segment, lo…
Read article →LinkedIn Architecture, in depth: the professional graph, the log at the centre, and derived data stores built from one source of truth
How LinkedIn's architecture is shaped by network distance and derived data: Espresso as source of truth, change capture into Kafka, Samza and bat…
Read article →Meta Threads Architecture
How Meta launched Threads in 5 days by leveraging Instagram's infrastructure. Covers authentication reuse, social graph leverage, database shardi…
Read article →PayPal P2P Architecture, in depth: a reference design for wallet-to-wallet money transfer
How a PayPal-style person-to-person payment system can work: what PayPal has and has not published, requirements, a double-entry ledger, an idempotent…
Read article →Range Sharding, in depth: the sorted range map, scans across boundaries, size and load splits, merges, monotonic-key hotspots and stale routing
How range sharding works and how to operate it: range descriptors and bisect routing code, scans that survive splits, size-based versus load-based spl…
Read article →Rate Limiter Architecture, in depth: GCRA in one Redis key, composite limits, local token leasing, failure policy and client signalling
How to build a production rate limiter rather than pick an algorithm: the decision contract, GCRA implemented as an atomic Redis script with server ti…
Read article →Recommendation System Architecture, Netflix-style, in depth: rows of rows, page construction, offline/nearline/online tiers, artwork bandits and fallbacks
How a streaming homepage is personalized as a whole page: generating candidate rows, ranking titles within rows, building a page with deduplication an…
Read article →Reddit Architecture, in depth: hot, best and controversial ranking, precomputed listings, the asynchronous vote path and comment trees
How Reddit's classic architecture serves sorted listings at scale, reconstructed from the open-source r2 code: the Thing data model, the exact ho…
Read article →REST API Design, in depth: HTTP method semantics, status codes, caching and validators, conditional writes, PATCH formats and long-running operations
REST API design at the HTTP layer: what safe, idempotent and cacheable methods promise to clients, caches and gateways; status codes clients can branc…
Read article →Robinhood Trading Architecture, in depth: a reference design for a retail broker, from the tap to settlement, and what the 2020 and 2021 incidents teach
A system design for a commission-free retail brokerage like Robinhood: order intake and idempotency, buying-power reservation, an order state machine,…
Read article →Amazon S3 Object Storage Internals, in depth: erasure-coding geometry, a worked durability model, end-to-end checksums, the storage node and the consistency witness
How an S3-scale object store keeps data: erasure-coding geometry against repair bandwidth, a durability model computed in code, correlated failures an…
Read article →API gateway architecture
Deep-dive on API gateway design: data plane vs control plane, route matching and filter chains, JWKS-cached auth, distributed rate limiting, retry bud…
Read article →Backpressure Architecture in Depth: Bounded Queues, Credit-Based Flow Control and Propagating Overload Upstream
How backpressure keeps systems stable when producers outrun consumers: bounded queues and Little's Law sizing, blocking versus credit signals ver…
Read article →Content Delivery Network Architecture in Depth
A 2500-word walkthrough of CDN architecture: client, edge PoP, origin shield, origin, cache rules, purge, optimization, TLS, edge compute, analytics, …
Read article →CQRS architecture
Deep-dive on CQRS (Command Query Responsibility Segregation): splitting the write model that validates commands and mutates a normalized source of tru…
Read article →Dead-letter queue architecture
Deep-dive on the dead-letter queue: the delivery counter and retry policy, broker-level vs application-level dead-lettering, the failure-metadata cont…
Read article →Distributed lock architecture
Deep-dive on distributed locks: consensus-backed lock services (etcd, ZooKeeper), lease TTLs and sessions, fencing tokens checked at the resource, wai…
Read article →Event sourcing architecture
Deep-dive on event sourcing: commands and aggregates that emit events, the append-only event store as source of truth, rehydrating state by replay, sn…
Read article →Geo-distributed systems -- serving the world with low latency
Deep-dive on geo-distributed systems: the latency/availability/law drivers, multi-region replicas, data placement, the speed-of-light consistency-vs-l…
Read article →Gossip protocol architecture - epidemic membership, failure detection, and anti-entropy
Deep-dive on gossip protocols: the SYN/ACK/ACK2 digest exchange and version merge, phi-accrual failure detection and suspicion lifecycle, anti-entropy…
Read article →Hot-key mitigation architecture
Deep-dive on surviving hot keys in sharded systems: why hashing concentrates load, approximate hotspot detection, edge caching for read-hot keys, key …
Read article →Idempotency architecture
Deep-dive on idempotency architecture: keys, dedupe store, retry policy, conflict handling, cross-service propagation, TTL, and audit.
Read article →Leader election architecture
Deep-dive on leader election: quorum-based campaigning, terms/epochs, leases and heartbeats for bounded failover, fencing tokens that neutralize a sta…
Read article →Load shedding -- dropping work to survive overload
Deep-dive on load shedding: the overload-collapse problem, rejecting excess load, serve-some-well-rather-than-all-badly, fail fast (early rejection), …
Read article →Notification System Architecture in Depth: fan-out, per-recipient decisions, channel adapters and feedback
Design a notification system: delivery guarantees and priority classes, outbox to fan-out to orchestrator, data model, decision code with quiet hours …
Read article →Transactional outbox architecture
Deep-dive on the transactional outbox pattern: why commit-then-publish dual writes lose or fabricate events, writing the event to an outbox table in t…
Read article →Pub/sub system design architecture
Deep-dive on pub/sub design: topics, partitions, consumers, delivery guarantees, retention, DLQ, schema registry, and metrics.
Read article →Distributed Rate Limiter Architecture in Depth
Distributed rate limiting as a coordination problem: central counters, static splits, periodic sync and token leasing compared with error bounds, Redi…
Read article →Rate limiting architecture, in depth: rate versus concurrency limits, adaptive limits and outbound throttling
Rate limiting as admission control: where to place rate and concurrency limits, sizing from load tests, AIMD and gradient adaptive limits, client-side…
Read article →Read-replica routing architecture
Deep-dive on routing reads to replicas safely: read classification, LSN/GTID write watermarks, session stores, byte vs time lag, replica ejection, pri…
Read article →Saga pattern architecture
Deep-dive on the saga pattern: orchestration vs choreography, the durable saga log, compensating transactions and pivot placement, idempotency keys an…
Read article →Scaling Patterns in Depth: Finding the Bottleneck, Doing the Capacity Math, and Choosing the Next Move
A bottleneck-first method for scaling a system: name the saturated resource, size it with Little's law and queueing arithmetic, use the Universal…
Read article →Search System Architecture in Depth
A 2500-word walkthrough of search architecture: docs, indexer, inverted index, query, hybrid retrieval, reranking, personalization, analytics, shardin…
Read article →Service discovery architecture
Deep-dive on service discovery: the health-checked registry, client-side vs server-side discovery, DNS and mesh-sidecar packagings, watches and cachin…
Read article →Database sharding architecture
Deep-dive on database sharding: choosing the shard key, range versus hash partitioning, the routing layer and shard directory, online rebalancing, per…
Read article →Service Mesh Architecture, in depth: how sidecar proxies intercept traffic, get their configuration and identity, what they cost and how they fail
How a sidecar service mesh actually works: injection, iptables redirection, xDS configuration from the control plane, SPIFFE identities and mTLS, one …
Read article →Shard Rebalancing Strategies, in depth
Shard rebalancing in depth: what to balance, fixed partitions versus split-merge versus consistent hashing, triggers with hysteresis, a greedy move pl…
Read article →Signal Protocol Architecture, in depth: PQXDH key agreement, the Double Ratchet, and a server that learns almost nothing
How the Signal Protocol delivers end-to-end encryption to devices that are usually offline: the system architecture and what the server stores, identi…
Read article →Slack Architecture, in depth: channels and threads, channel and gateway servers, Vitess sharding by channel, and the Flannel edge cache
How Slack delivers channel and thread messages, from Slack's published engineering accounts: the conversation and thread data model, channel, gat…
Read article →Snapchat Ephemeral Messaging Architecture, in depth: view state, expiry, crypto-shredding and the leaks that defeat deletion
A system design for Snapchat-style ephemeral messaging: what disappearing messages can and cannot promise, a data model with per-recipient view state,…
Read article →Spotify Music Streaming Architecture, in depth
Designing a Spotify-style music service: quality tiers and track sizes, ingest, the playback path with prefetch, multi-CDN delivery, offline keys, rev…
Read article →Stock Exchange Matching Engine Architecture, in depth
How an exchange matching engine works: price-time priority, order book layout, the matching loop, order types, sequencer and journal, replication, mar…
Read article →Stripe Payment Platform Architecture, in depth: PaymentIntents, idempotency keys, signed webhooks, API versioning and the ledger behind them
How Stripe's payment platform is built as seen from both sides: the PaymentIntent state machine, idempotency as an API primitive, signed and retr…
Read article →Backend for Frontend (BFF), in depth: per-client backends, aggregation, token handling and when not to build one
The Backend for Frontend pattern from first principles: why one general-purpose API serves many clients badly, how a BFF differs from an API gateway a…
Read article →Caching
An orienting map of caching: the tiers a byte can live in, cache-aside versus write-through, why invalidation deletes rather than updates, the fill ra…
Read article →Event-Driven Architecture, in depth: events versus commands, the four styles, producer and consumer contracts, ordering, evolution and when not to use it
A decision framework for event-driven architecture: what an event is and is not, notification versus event-carried state transfer versus event sourcin…
Read article →API Gateway Pattern, in depth: when to add one, topologies, request composition under deadlines, identity propagation and versioning
The API gateway pattern from first principles: the client-to-microservice problem it solves, what belongs in a gateway and what does not, single gatew…
Read article →Leader-Follower Replication, in depth: the replicated log, high watermarks, epochs, follower truncation and the read contract
How leader-follower replication works as a replicated log: log end offsets and the high watermark, acknowledgement policies, a running failover simula…
Read article →Load Balancing
How load balancers distribute traffic across backend servers: L4 vs L7, round-robin vs least-connections, and health-check design.
Read article →Message Queues
The main message queue types (log-based Kafka vs broker-based RabbitMQ vs managed SQS), semantics (at-least-once vs at-most-once vs exactly-once), and…
Read article →Microservices Architecture, in depth: service boundaries, data ownership, synchronous versus asynchronous calls, failure arithmetic, a worked checkout and when a modular monolith wins
Microservices from first principles: what makes a service independent, drawing boundaries around data ownership, choosing synchronous or event-driven …
Read article →Payment System Design, in depth
Payment system design for multiple providers: separating payments from attempts, a pure routing function with circuit breakers, resolving unknown outc…
Read article →Rate Limiter Design, in depth: requirements, placement, rule model, counter choice, capacity and shadow rollout
How to design a production rate limiter from requirements to rollout: turning limits into a contract, choosing the layer, a descriptor-based rule mode…
Read article →Saga Orchestration, in depth: building the orchestrator, step ordering around the pivot, commands over an outbox, timeouts, recovery and isolation
How to build and run a saga orchestrator: a persisted state machine, compensatable, pivot and retriable steps, commands and replies through a transact…
Read article →Sharded Architecture, in depth: sharding the whole service stack, tenant placement, cross-shard work and moving tenants
How to design and run a service where the whole stack is sharded, not just the database: what lives inside a shard and what stays global, the edge rou…
Read article →Twitter-Style Feed Design, in depth: requirements, capacity math, Snowflake IDs, hybrid fan-out, cursors and consistency
Designing a Twitter-style home feed from first principles: requirements, capacity arithmetic, a data model with time-sortable Snowflake IDs, a hybrid …
Read article →Large File Upload Design, in depth: chunking, resumable protocols, parallel parts and the client upload engine
Designing uploads that survive real networks: why single requests fail, tus versus multipart, part sizing within S3 limits, parallelism and the bandwi…
Read article →Video Platform Design (YouTube-Style), in depth: the control plane, from video lifecycle and playback sessions to resume and takedown propagation
The control plane of a YouTube-style video platform: an explicit video lifecycle state machine with an outbox, a playback-session API that decides acc…
Read article →Telegram Architecture, in depth: MTProto 2.0, data centres, the update sequence, file and CDN delivery, and secret chats
How Telegram works as documented in its public protocol: MTProto transport and encryption layers, per-DC authorization keys and migration, pts/qts/seq…
Read article →TikTok Architecture, in depth: a short-video feed that learns from every swipe, from upload and CDN to retrieval, ranking and minute-level online training
A reference architecture for a TikTok-style short-video recommendation feed: what the product demands, upload and delivery with client prefetch, multi…
Read article →Twitter Timeline Generation Architecture, in depth: the Following cache, the For You ranking pipeline, and how both are served, repaired and kept fast
How Twitter-style home timelines are generated: the precomputed Following timeline cache and its fan-out workers, read-time merging and visibility fil…
Read article →UPI Architecture, in depth: how India's real-time payment network routes, authenticates, settles and recovers from timeouts
How the Unified Payments Interface works as a system: the four parties around NPCI's central switch, VPA resolution, device binding and issuer-ve…
Read article →Vector Search at Scale, in depth: segments, capacity math, sharding, filtering, re-embedding and recall in production
How to design a vector search service for hundreds of millions of embeddings: separate write and read paths, growing and sealed segments, worked memor…
Read article →Video Streaming Architecture, in depth: ingest, chunked transcoding, bitrate ladders, HLS/DASH/CMAF packaging, CDN design, adaptive bitrate players and QoE
A system design walkthrough of a Netflix-style video-on-demand platform: requirements and capacity math, chunked parallel transcoding, per-title ladde…
Read article →Website Hosting Architecture, in depth: DNS, TLS, CDN, origins and a deploy pipeline that never serves a broken page
End-to-end website hosting architecture: the five planes (naming, edge, origin, build and deploy, observation), choosing between static, static plus A…
Read article →WeChat Super-App Architecture, in depth: sequence-number sync, Paxos storage, DAGOR overload control, mini programs and payments
How a super-app like WeChat is built, separating what Tencent has published from a labelled reference design: one long connection, message sync by per…
Read article →WhatsApp Architecture, in depth: persistent connections, store-and-forward, Signal sessions, client fan-out for multi-device, Sender Keys for groups and encrypted media
How WhatsApp delivers end-to-end encrypted messages at scale: the long-lived connection layer, a routing registry and 30-day offline queue, prekeys an…
Read article →YouTube Architecture, in depth: designing a user-generated video platform for uploads, processing pipelines, sharded metadata, view counting and edge delivery
A system design walkthrough of a YouTube-scale user-generated video platform: requirements and scale, resumable uploads, a per-video processing DAG wi…
Read article →Zoom Video Conferencing Architecture, in depth: layered video, multimedia routers, transport fallback and encryption
How Zoom-style conferencing works: one scalable-video stream per sender, routers that forward layers instead of transcoding, a UDP-to-TLS transport la…
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