L1 · READ-DOMINANT · STEP 51Level 1: Core Building Blocks
Distributed URL Shortener & Redirection Engine
Design a planetary-scale link shortening service with Base62 range allocation, distributed cache tiers, and Bloom filter redirection.
Workload ProfileRead/Write 100:1, Zipfian hot keys, p99 < 10 ms
Key Engineering Challenges- Token collision avoidance
- Cache stampede under celebrity links
- Single-flight caching
L1 · TRAFFIC SHAPING · STEP 39Level 1: Core Building Blocks
Adaptive Distributed Rate Limiter
Protect upstream services using Token Bucket and Sliding Window counters in Redis with local caching and load shedding.
Workload ProfileOverload spikes 10x, sub-millisecond check latency
Key Engineering Challenges- Redis atomicity via Lua scripts
- Race conditions in multi-region
- Fail-open vs fail-close
L1 · FAN-OUT QUEUES · STEP 54Level 1: Core Building Blocks
Distributed Multi-Channel Notification Engine
Architect reliable dispatch across push, SMS, and email with recipient throttling, priority queues, and delivery guarantees.
Workload ProfileHigh-fanout writes, third-party rate limits, deduplication
Key Engineering Challenges- Provider quota throttling
- Idempotent deduplication windows
- Priority inversion prevention
L1 · IN-MEMORY CACHING · STEP 27Level 1: Core Building Blocks
Distributed Object Cache & Stampede Mitigation
Design multi-tiered cache-aside architectures with probabilistic early expiration (XFetch) and single-flight request grouping.
Workload ProfileSub-millisecond memory lookups, hot-key clustering
Key Engineering Challenges- Dogpiling / cache stampedes
- Consistent hash rebalancing
- Invalidation races under replication lag
L1 · BLOB STORAGE · STEP 52Level 1: Core Building Blocks
Distributed Object Storage & Multipart CDN
Separate metadata from binary data chunks, implement SHA-256 content addressing, multipart uploads, and edge CDN routing.
Workload ProfileLarge payload streaming (10MB-50GB), petabyte scale
Key Engineering Challenges- Multipart chunk assembly & deduplication
- Byte-range streaming HTTP 206
- Consistency between metadata and block storage
L2 · GRAPH FAN-OUT · STEP 57Level 2: Workload-Specific Systems
Social Feed & Activity Stream Architecture
Design activity streams handling normal users via write fan-out and high-follower celebrities via lazy read pull.
Workload ProfileExtreme celebrity skew (1:10M), hybrid push/pull
Key Engineering Challenges- Celebrity timeline explosion
- Cursor-based pagination under live inserts
- Timeline cache hydration
L2 · BIDIRECTIONAL WEBSOCKETS · STEP 55Level 2: Workload-Specific Systems
Real-Time Chat & Distributed Presence Platform
Architect a full-duplex messaging system with connection pinning, distributed presence heartbeats, and message sequencing.
Workload Profile50M concurrent WebSocket connections, sub-100ms message delivery
Key Engineering Challenges- Connection drain during rolling upgrades
- Ephemerality vs persistence of presence
- Guaranteed message ordering per conversation
L2 · LEXICAL SEARCH · STEP 58Level 2: Workload-Specific Systems
Distributed Prefix Search & Autocomplete Engine
Build an autocomplete suggestion system using in-memory Finite State Transducers (FST), trie indexes, and distributed ranking.
Workload ProfileLow-latency keystroke prefix search (p99 < 15ms), BM25 ranking
Key Engineering Challenges- Index memory sizing
- Near-real-time index updates without locking
- Fuzzy typo tolerance (Levenshtein automatons)
L2 · ZERO-DRIFT ACID · STEP 59Level 2: Workload-Specific Systems
Financial Ledger & Double-Entry Bookkeeping
Immutable double-entry transaction ledgers with distributed idempotency keys, hot account contention sharding, and reconciliation.
Workload ProfileStrict serializability, 100% balance auditability, idempotency
Key Engineering Challenges- Hot account row-lock serialization
- Two-phase commit vs Outbox Sagas
- Automated reconciliation under partial failures
L2 · HIGH-BANDWIDTH MEDIA · STEP 53Level 2: Workload-Specific Systems
Global Video Streaming & Transcoding Pipeline
Ingest raw video, slice into HLS/DASH segments, transcode across multiple bitrates asynchronously, and serve via edge CDNs.
Workload ProfileMulti-gigabit video egress, adaptive bitrate (ABR), global CDNs
Key Engineering Challenges- Distributed transcoding DAG scheduling
- Adaptive bitrate manifest generation
- Edge cache hit-ratio optimization
L3 · HIGH-CONTENTION BURSTS · STEP 60Level 3: Complex Business Systems
High-Concurrency Flash-Sale & Ticket Booking
Handle viral ticket drops using virtual waiting rooms, Redis Lua atomic reservation holding, and TTL checkout expiration.
Workload Profile100x traffic burst, extreme inventory contention, 0% oversell
Key Engineering Challenges- Inventory overselling prevention
- Database connection pool collapse
- Abandoned cart inventory rollback
L3 · CONCURRENT MUTATIONS · STEP 56Level 3: Complex Business Systems
Real-Time Collaborative Editing: OT vs CRDT
Design collaborative text editors comparing Operational Transformation (central server) with Conflict-free Replicated Data Types.
Workload ProfileMulti-user concurrent document mutations with zero central locking
Key Engineering Challenges- Causal ordering via vector clocks
- Intention preservation under concurrent typing
- State vector compression & tombstone garbage collection
L3 · TENANT ISOLATION · STEP 61Level 3: Complex Business Systems
Multi-Tenant Enterprise SaaS Architecture
Pool vs Silo architectures, PostgreSQL Row-Level Security, per-tenant hierarchical token bucket limits, and BYOK encryption.
Workload Profile10,000 pooled enterprise tenants, strict SLA and data boundaries
Key Engineering Challenges- Noisy neighbor resource starvation
- Tenant-aware connection pooling
- Cross-tenant data leakage prevention
L3 · GLOBAL RESILIENCY · STEP 62Level 3: Complex Business Systems
Global Multi-Region Active-Active Architecture
Active-active multi-datacenter data routing using BGP Anycast, Spanner TrueTime, and CockroachDB Hybrid Logical Clocks.
Workload ProfileWorldwide user traffic, regional data sovereignty, WAN replication
Key Engineering Challenges- WAN speed-of-light replication latency
- Split-brain regional partitions
- Data sovereignty & GDPR regional residency
L4 · REPLICATED LOGS · STEP 43Level 4: Infrastructure Platforms
Distributed Commit Log Broker (Kafka Internals)
Architect a partitioned append-only distributed commit log using sequential disk I/O, zero-copy network sends, and ISR replication.
Workload Profile1M+ messages/s, zero-copy socket transfers, partition ISRs
Key Engineering Challenges- Page cache write saturation
- Leader election during broker crash
- Consumer group rebalance storms
L4 · FORMAL CONSENSUS · STEP 45Level 4: Infrastructure Platforms
The Raft Consensus State Machine
Implement a distributed consensus engine with leader election, term monotonicity, log replication invariants, and joint consensus.
Workload ProfileStrict linearizability, majority quorums, split-brain immunity
Key Engineering Challenges- Split-vote election deadlocks
- Non-committed log rollback
- Dynamic cluster reconfiguration
L4 · EVENTUAL CONSISTENCY · STEP 47Level 4: Infrastructure Platforms
Decentralized Dynamo-Style Key-Value Store
Peer-to-peer ring topology using consistent hashing, vector clock conflict detection, hinted handoff, and anti-entropy Merkle trees.
Workload ProfileHigh write availability, tunable quorums (W + R > N), gossip
Key Engineering Challenges- Replica divergence under network partitions
- Sloppy quorum read anomalies
- Merkle tree anti-entropy overhead
L4 · MULTI-RAFT TRANSACTIONS · STEP 48Level 4: Infrastructure Platforms
Distributed SQL & Multi-Raft Consensus
Architect a distributed SQL database using Multi-Raft range groups, automated range splitting, and Percolator decentralized 2PC.
Workload ProfileHorizontally scalable SQL with ACID cross-shard 2PC
Key Engineering Challenges- Cross-range distributed transactions
- Range split & merge coordination
- Hot spot range rebalancing
L4 · AI INFERENCE SERVING · STEP 84Level 4: Infrastructure Platforms
High-Throughput LLM Inference Serving Platform
Design a modern LLM serving system implementing iteration-level continuous batching, chunked prefill, and virtual KV cache paging.
Workload ProfileDisaggregated prefill/decode, PagedAttention, KV cache management
Key Engineering Challenges- GPU memory fragmentation from KV caches
- Prefill vs decode scheduling interference
- TTFT vs ITL latency trade-offs
L4 · ACCELERATOR ORCHESTRATION · STEP 86Level 4: Infrastructure Platforms
GPU Cluster Scheduling & Gang Orchestration
Architect a multi-tenant GPU orchestrator accounting for NVLink/InfiniBand locality, all-or-nothing allocation, and node drain.
Workload ProfileAll-or-nothing gang scheduling across 1,000+ GPUs, topology awareness
Key Engineering Challenges- Job starvation & Head-of-Line blocking
- Topology-unaware placement degrading Ring-AllReduce
- Elastic worker fault tolerance
L4 · EMBEDDING RETRIEVAL · STEP 85Level 4: Infrastructure Platforms
Distributed Vector Database & Hybrid Search
Design a distributed vector database with Hierarchical Navigable Small World (HNSW) graphs, Product Quantization (PQ), and metadata filtering.
Workload ProfileBillion-scale embedding retrieval, p99 < 20 ms, hybrid BM25 + HNSW
Key Engineering Challenges- Index memory footprint at scale
- Real-time embedding insertion into HNSW graphs
- Recall degradation under aggressive quantization
L5 · CAPSTONE 01 (PART 8) · STEP 91Level 5: Flagship Capstones (Part 8)
Capstone 1: Global Flash-Sale & High-Concurrency Commerce Engine
Synthesize edge rate limiting, atomic Redis seat reservation holds, and idempotent double-entry payment settlement into a zero-drift commerce engine.
Workload Profile100,000 RPS burst, zero overselling, transactional outbox settlement
Key Engineering Challenges- 50x flash-sale admission control
- Atomic inventory lease expiration
- Zero double-charging across retries
L5 · CAPSTONE 02 (PART 8) · STEP 92Level 5: Flagship Capstones (Part 8)
Capstone 2: Linearizable Replicated Key-Value & Coordination Store
Combine an append-only WAL + LSM storage engine with Multi-Raft consensus replication, consistent hash placement, and Phi accrual failure detection.
Workload ProfileLinearizable quorum reads/writes, < 1.2s leader failover, LSM engine
Key Engineering Challenges- Split-brain fencing with epoch leases
- Log compaction & snapshot install
- Dynamic range split rebalancing
L5 · CAPSTONE 03 (PART 8) · STEP 93Level 5: Flagship Capstones (Part 8)
Capstone 3: Disaggregated LLM Inference & PagedAttention Serving Platform
Build an iteration-level continuous batching scheduler with prefill/decode disaggregation, PagedAttention virtual KV block tables, and prefix caching.
Workload ProfileTTFT p95 < 180ms, ITL p95 < 22ms/token, < 4% KV waste
Key Engineering Challenges- Eliminating KV cache external fragmentation
- Prefill/decode KV transfer bandwidth
- Token-level backpressure & SLA routing
L5 · CAPSTONE 04 (PART 8) · STEP 94Level 5: Flagship Capstones (Part 8)
Capstone 4: Multi-Tenant Hybrid RAG & Durable Agentic Execution Platform
Architect streaming ingestion, hybrid HNSW + BM25 retrieval with Reciprocal Rank Fusion, tenant ACL pre-filtering, and durable agentic workflow graphs.
Workload ProfileRecall@10 >= 0.94, p99 < 65ms retrieval, strict tenant ACL isolation
Key Engineering Challenges- Zero cross-tenant vector leakage
- Durable tool-call checkpointing
- Semantic cache invalidation & grounding