System Design
BigCat's Architecture Lab
> Distributed · Scalability · Real-world Case Studies
Day 01
Scalability Foundations
Vertical/Horizontal · L4/L7 LB · Stateless · Capacity Planning
Day 02
Caching
Cache Layers · LRU/LFU/ARC · Cache-aside · Invalidation
Day 03
Database Selection
SQL/NoSQL · OLTP/OLAP · ACID/BASE · Decision Tree
Day 04
Database Sharding
Hash/Range · Consistent Hashing · Hot Spots · Resharding
Day 05
Replication
Leader/Multi/Leaderless · Sync/Async · Replication Lag · Failover
Day 06
Consistency
Linearizable/Causal/Eventual · CAP/PACELC · HLC · Per-domain Choice
Day 07
Distributed Transactions
2PC/3PC · Saga · Outbox · Idempotency
Day 08
Message Queues
Kafka/RabbitMQ/SQS · Delivery Semantics · Backpressure · DLQ
Day 09
API Design
REST/GraphQL/gRPC · Pagination · Versioning · Rate-Limit Contract
Day 10
Rate Limiting
Token/Leaky/Sliding/GCRA · Distributed Counters · Multi-dim · 429 Contract
Day 11
Unique ID Generation
UUIDv4/v7 · Snowflake · ULID/KSUID · Clock Skew
Day 12
Search Systems
Inverted Index · Lucene Segments · Scatter-Gather · Vector HNSW
Day 13
Recommendation Systems
Two-Tower Retrieval · Multi-stage Funnel · Cold Start · Generative Rec TIGER
Day 14
Feed System
Push/Pull/Hybrid · Fanout Amplification · Timeline Storage · Ranking Pipeline
Day 15
Chat System
WebSocket Connections · Bucketed Storage · Delivery Guarantees · E2E Encryption
Day 16
Video Streaming
Transcode Pipeline · Per-Title/Per-Shot · ABR · CDN/Open Connect
Day 17
Payment Systems
Idempotency Recovery Points · Double-Entry Ledger · Saga/Outbox · 3-Way Reconciliation
Day 18
Subscription & Billing
Lifecycle State Machine · By-Second Proration · Usage Metering · Multi-currency & Tax
Day 19
Geospatial Systems
Geohash/S2/H3 · Grid vs R-Tree · haversine/ETA · Uber DISCO Geo-Sharding
Day 20
Data Processing (Batch vs Stream)
Batch/Stream Unify · Lambda/Kappa · Event-time/Watermark · Exactly-once
Day 21
Monitoring & Observability
Metrics/Logs/Traces · OpenTelemetry Sampling · SLO/Error Budget · Percentile Aggregation
Day 22
Deployment & Release
Rolling/Blue-Green/Canary · Canary Analysis · Feature Flags · Expand-Contract Migration
Day 23
Reliability
Circuit Breaker FSM · Backoff+Jitter Retry · Bulkhead Isolation · Graceful Degradation & Load Shedding
Day 24
Security
AuthN/AuthZ Boundary · OAuth2/OIDC + PKCE · JWT vs Session Revocation · Secret Dynamic Creds
Day 25
System Design Interview
Scoping · 4-Step Framework + Time-boxing · Think Out Loud & Deep Dive · Articulating Trade-offs
Day 26
Capacity Estimation
Powers of 2 + Latency Numbers · DAU→QPS Peak · Storage/Bandwidth/Memory · Assumption Discipline
Day 27
Cost & Capacity Engineering
Queueing Headroom · Reactive/Predictive Autoscaling · FinOps Attribution · Rightsizing/Spot Tiers
Day 28
CDN & Edge
Anycast/BGP · Tiered Cache Funnel · Purge/SWR Invalidation · Edge Compute V8 Isolate
Day 29
File & Object Storage
Object vs Block vs File flat keyspace · Replication vs Erasure Coding 11 nines · Multipart + presigned direct upload · Strong metadata consistency & hot partitions
Day 30
Authorization & Account Systems
RBAC/ABAC/ReBAC relation tuples · Hierarchical inheritance & Zookie revocation · Multi-tenant RLS isolation · Hash-chained tamper-evident audit
Day 31
Hybrid Search & Reranking
BM25 vs dense vectors complementary · Recall/rerank multi-stage funnel · RRF fusion & cross-encoder reranking · Query-biased snippet highlighting
Day 32
LLM Serving
Two-phase inference & continuous batching · KV Cache/PagedAttention memory bottleneck · Prompt caching & prefix-aware routing · Cost/Latency/Quality triangle
Day 33
AI Product Backend
RAG recall quality contextual+hybrid+rerank · Durable resumable agent loops · Embedding service model/index version locking · Human-in-the-loop approval gate
Day 34
Real-time Systems
TCP head-of-line blocking & UDP/WebRTC/QUIC channels · Client prediction + server reconciliation + interpolation · Authoritative server tick/delta/AOI state sync · Collab editing OT/CRDT/LWW (Figma)
Day 35
IoT & Edge
MQTT pub/sub & tiered QoS · Edge reduction + offline buffering · Kafka peak-shaving/decouple/backpressure · TSDB Gorilla compression & cardinality explosion
Day 36
Blockchain & Distributed Ledger
PoW/PoS/BFT consensus & Sybil resistance · Smart-contract determinism + gas + reentrancy · Hash chain/Merkle/off-chain storage availability · Trilemma & L2 Rollups (Optimistic vs ZK)
Day 37
Multi-tenant SaaS
Silo/Pool/Bridge isolation spectrum · Shard by tenant_id + RLS for leak/skew control · Noisy-neighbor per-tenant limiting + fair queues · Idempotent recomputable usage metering
Day 38
Data Lake & Lakehouse
Lake/warehouse/lakehouse selection & open columnar · ACID on S3 with Iceberg/Delta/Hudi (immutable files + atomic snapshot swap + OCC) · Layered-metadata pruning + time travel + small-file ops · Unified batch/stream COW vs MoR & incremental ETL
Day 39
Workflow Engine
Durable execution: event-sourcing + deterministic replay · Orchestration vs choreography · Saga compensation (semantic undo) + backward/forward recovery · Activity at-least-once + idempotency key + heartbeat/timeout