Blog
User guides for hongry.dev services and in-depth articles on web and backend engineering.
User guides
Finding Public Amenities Near You: Open Data Limits & Public-Lens Guide
Where public facility data for restrooms, pharmacies, emergency bells, and shelters comes from, what update delays to keep in mind, and how to search all 19 categories on Public-Lens.
How to Check EV Charging Stations Before a Long Drive: EV-Lens Practical Guide
How to verify your EV's connector type (DC Combo, CHAdeMO, AC 3-Phase), pick primary and backup fast chargers along your route, and check real-time stall availability on EV-Lens.
How to Track Your Mood Without Pressure: Building a Routine with MoodCast
Why logging your mood as weather helps create healthy emotional distance, how to record a day in one line, and how to review monthly patterns on the MoodCast calendar.
Why In-Browser Processing Is Safer & How to Use anyTools' 30 Utilities
Compares server-upload converters with client-side browser processing, shows how to verify zero uploads in the DevTools Network tab, and walks through all 30 utilities in anyTools.
How to Read KMA Neighborhood Forecasts & Check Weather Before Heading Out
Understand the KMA 5 km forecast grid, release schedules, precipitation probability, feels-like temperature, and fine dust grades, plus a 6-step pre-departure weather check sequence.
Step-by-Step Preparation on Ticketing & Course Registration Day with TrueTime
A chronological preparation guide for concert ticketing and university course registration: checking target domain server clocks 30 minutes early, testing the 10-second pre-alarm, and understanding server clock limits.
Engineering articles
Implementing Distributed Locks with Redis: Go, NestJS, Redisson & Fencing Tokens
How to implement Redis distributed locks safely with atomic SET NX PX and token-checking Lua scripts across Go, NestJS, and Spring Boot Redisson, plus why fencing tokens matter for data integrity.
Lightweight Distributed Locks with PostgreSQL Advisory Locks & MySQL GET_LOCK
How to prevent duplicate cron job execution across multiple servers without Redis using PostgreSQL pg_try_advisory_xact_lock and MySQL GET_LOCK, including connection pool and PgBouncer caveats.
Database Concurrency Control: Pessimistic Lock vs. Optimistic Lock in Practice
Compares atomic SQL UPDATEs, pessimistic locking (SELECT FOR UPDATE), and optimistic locking (version columns) for preventing Lost Updates, with Go GORM, NestJS Prisma, and Spring Data JPA examples.
Cache Stampede Causes & Mitigations: singleflight, Distributed Locks, and XFetch
Why database load spikes when hot cache keys expire under heavy traffic, and how to prevent it using Go singleflight, NestJS in-flight Promise sharing, XFetch probabilistic refresh, and TTL jitter.
Designing Payment & Mutation APIs: Idempotency-Key Implementation Guide
How API idempotency prevents duplicate charges from network retries and double clicks, complete with SQL storage schema design, a NestJS RxJS interceptor example, and production pitfalls.
Differences Between URL Encoding (Percent-Encoding) and HTML Entity Encoding
Compares RFC 3986 URL percent-encoding with HTML entity escaping for XSS defense, shows how both interact in a single request lifecycle, and covers encodeURIComponent vs encodeURI pitfalls.
Why Large JSON Freezes the Browser & Optimizing with Web Workers and Virtual Scrolling
Why synchronous JSON.parse() and massive DOM trees freeze browser tabs, how to offload formatting to Web Workers and Virtual Scrolling, and 5 common JavaScript JSON pitfalls.
Base64 Encoding Principles: Why 3 Bytes Become 4 Characters & UTF-8 Examples
Understand how Base64 slices 24-bit groups into four 6-bit ASCII characters, follow a step-by-step UTF-8 Korean encoding trace, and fix btoa() InvalidCharacterError using TextEncoder.
Map Projection Types & KMA Grid Conversion (Lambert Conformal Conic) Explained
Explains conformal, equal-area, and equidistant map projections and walks through converting GPS latitude/longitude into KMA 5 km (nx, ny) grid coordinates using the Lambert Conformal Conic projection in JavaScript.
HTML5 Geolocation API Accuracy Limits & Handling Location Errors
How the browser Geolocation API resolves position via GPS, Wi-Fi (WPS), Cell-ID, and IP, how to interpret the 95% confidence radius (accuracy), and how to filter noisy coordinates with the Haversine formula.
Understanding Differences Between WGS84 & UTM-K Coordinate Systems
Compares the global WGS84 (EPSG:4326) geographic coordinate system with Korea's national UTM-K (EPSG:5179) planar system using real Seoul City Hall conversion examples and common axis-order pitfalls.