System Design

⏱ 3 min read Data Model EmailTemplate ( id SERIAL PRIMARY KEY, name VARCHAR NOT NULL, locale VARCHAR NOT NULL DEFAULT ‘en’, subject_template TEXT […] Read article

⏱ 3 min read Template Syntax Core syntax: {{variable}} for variable substitution, {{#if condition}}…{{/if}} for conditionals, {{#each items}}…{{/each}} for loops, {{> partial_name}} for partials, Read article

⏱ 4 min read What Is a Request Routing Service? A request routing service directs incoming HTTP requests to the appropriate upstream based on Read article

⏱ 4 min read What Is an Access Log Service? An access log service captures structured HTTP request/response details from every service in the Read article

⏱ 4 min read Shipment Tracking Service: Low Level Design Core Data Model The tracking service maintains two primary tables: Shipment (one record per Read article

⏱ 5 min read Returns Processing System: Low Level Design Core Data Model Two primary tables capture return requests and the individual items within Read article

⏱ 3 min read Presence States online — active heartbeat within the last 30 seconds away — active within the last 5 minutes but Read article

⏱ 3 min read Ephemeral State Design Typing state is intentionally ephemeral — stored only in Redis, never persisted to the database. There is Read article

⏱ 3 min read Graph-Based Recommendation Engine Model the recommendation problem as a graph: users and items are nodes, interactions are weighted edges. Graph Read article

⏱ 4 min read What Is an Anomaly Detection Service? An anomaly detection service monitors time-series metrics and identifies values that deviate significantly from Read article

⏱ 4 min read What Is a Rule Engine? A configurable rule engine evaluates business logic defined as structured data rather than code. Rules Read article

⏱ 3 min read WebAuthn / FIDO2 Overview Passkeys use public-key cryptography. The private key never leaves the device; the server stores only the Read article

⏱ 3 min read Data Model Closure table for efficient subtree queries: ThreadAncestor ( ancestor_id BIGINT, descendant_id BIGINT, depth INT, PRIMARY KEY (ancestor_id, descendant_id) Read article

⏱ 3 min read Schema Reaction ( entity_type VARCHAR(50), entity_id BIGINT, user_id BIGINT, reaction_type ENUM(‘like’,’love’,’haha’,’wow’,’sad’,’angry’), created_at TIMESTAMP, PRIMARY KEY (entity_type, entity_id, user_id) ) ReactionCount Read article

⏱ 3 min read PoP Selection and GeoDNS When a client issues a DNS query, GeoDNS maps the client IP to a geographic region Read article