CDN Edge Cache Low-Level Design: Cache Hierarchy, Origin Shield, Cache Invalidation, and Routing
CDN Edge Cache: What It Does A content delivery network (CDN) accelerates content delivery by caching responses at Points of […]
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Metrics Aggregation Service Low-Level Design: Time-Series Ingestion, Downsampling, and Query Engine
Metrics Aggregation: Purpose and Scope A metrics aggregation service collects numeric measurements from infrastructure and applications, stores them as time
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Alerting System Low-Level Design: Alert Evaluation, Deduplication, Routing, and On-Call Escalation
Alerting System: Goals and Challenges An alerting system monitors metrics and fires notifications when conditions violate defined thresholds. The central
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Web Crawler Low-Level Design: URL Frontier, Politeness Policy, and Distributed Crawl Coordination
Web Crawler: Core Architecture A web crawler fetches web pages at scale, extracts links, and feeds them back into the
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Order Management System Low-Level Design: Order State Machine, Inventory Reservation, and Fulfillment Coordination
Order State Machine An order progresses through a defined set of states with controlled transitions: CART → PLACED → PAYMENT_PENDING
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Sliding Window Counter Rate Limiter Low-Level Design: Hybrid Algorithm, Redis Sorted Sets, and Accuracy Trade-offs
Fixed Window Counter and Its Problem The simplest rate limiter increments a counter per time window and resets it at
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Schema Evolution Low-Level Design: Protobuf Compatibility, Avro Schema Registry, and Forward/Backward Compatibility
Compatibility Definitions Schema evolution is the ability to change a data schema over time without breaking producers and consumers that
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Backward Compatibility Low-Level Design: Tolerant Reader, Postel’s Law, and API Contract Testing
The Tolerant Reader Pattern The tolerant reader pattern (Martin Fowler, 2011) describes how a service should consume data from external
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Bulkhead Pattern Low-Level Design: Thread Pool Isolation, Semaphore Bulkheads, and Resource Partitioning
The Bulkhead Analogy A ship's hull is divided into watertight compartments (bulkheads). If one compartment floods, the others remain dry
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Retry Policy Low-Level Design: Exponential Backoff, Jitter, and Idempotent Retry Safety
Why Retry Policies Matter Transient failures — network blips, momentary overload, upstream restarts — are normal in distributed systems. A
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Idempotency Service Low-Level Design: Idempotency Keys, Request Deduplication, and Response Caching
What Is an Idempotency Service? An idempotency service ensures that duplicate requests — caused by client retries, network timeouts, or
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Conflict-Free Replication Low-Level Design: CRDTs, Operational Transforms, and Convergent Data Types
What Are CRDTs? A Conflict-free Replicated Data Type (CRDT) is a data structure with a mathematically defined merge operation that
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Read Scaling Architecture Low-Level Design: Read Replicas, Read-Through Cache, CQRS, and Query Routing
Read Scaling Overview Read scaling addresses the most common bottleneck in production systems: reads vastly outnumber writes (often 10:1 to
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Write Scaling Architecture Low-Level Design: Sharding, Write Batching, Async Processing, and CQRS Command Side
The Write Scaling Bottleneck In a standard primary-replica setup, all writes go through a single primary database. The primary's write
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Active-Active Architecture Low-Level Design: Multi-Region Writes, Conflict Resolution, and Global Load Balancing
What Is Active-Active Architecture? In an active-active architecture, multiple regions (or data centers) simultaneously accept writes and serve reads. Every