A mid-project retrospective on a personal automated trading platform built with Rust + Python + React. With ETF rebalancing and single-stock signal trading both in place, a record of how the safety layers — halt, block, detect, simulate — got built before going live.
A good engineer isn’t someone who knows technology well, but someone who can share that knowledge with their team.
A retrospective on column-level encryption of sensitive data in a running service. Envelope encryption, DEK granularity decisions, the WHERE clause constraint that led to HMAC, and the migration automation Skill that spread the work across the org.
A retrospective on the internal hackathon. How an idea I proposed evolved with the team into a 1st-place project and an internal launch — and the starting point for using AI tools in earnest.
Retrospective on building a system that automatically identifies low-performing SSP inventory and throttles traffic to improve contribution margin. Covers the evolution from Imp Cost Ratio to a predicted contribution margin rate approach.
Building my first ML Lifecycle — a three-tier architecture for an ad Fallback CTR prediction — as a backend engineer without an AI background. The technical decisions I made, and what I learned through running it.
An external event drove ad traffic far above normal, triggering a cascading failure. The real problem was that the filtering component was a single point of failure — and the fallback sat on top of it too, so one collapse pulled both down at once. The fix took three paths: removing the fallback’s dependency (independence), adding rate limiting to the component itself (protection), and reconsidering the runtime (throughput).
The deploy was two days old, and the metrics had been calm the whole time. The moment we turned off the cache refresh batch, ad serving stopped. A retrospective on the missing verification of what a deploy actually changed.
A record of implementing and benchmarking three Go concurrency patterns — mutex, channel, and lock-free — to build hands-on understanding.
A record of designing and building a chat system as a personal project to gain hands-on experience with Kafka and Hexagonal Architecture.
Designing a Nest.js-based fallback server while removing a legacy ad server. Why a horizontal layered architecture fit better than Nest.js’s default vertical module slicing for a single API with complex business logic.
How I reduced network costs and enabled instance downscaling by switching from full cache refresh to incremental refresh for campaign configuration data.
A retrospective on moving ad budget pacing from a fixed-rule scheme to a two-layer control loop — per-campaign learning sets the baseline, real-time correction absorbs drift.
A record of implementing the multithreaded HTTP server from Rust Book Chapter 20, experiencing how ownership and concurrency safety are enforced at the type level.
SwapDo, a deepfake-based face synthesis meme service. A record of five months as a developer and team lead in a startup team.
A startup born from a casual League of Legends habit. From architecture design to desktop apps, a record of two people building a service that grew to 10,000 users over five months.
Entering the GDG Korea Android 11 Hackathon solo, building both server and app in three weeks.
Korea Railroad Industry Information Center’s public-data hackathon. A three-person team built an Android app that surfaces hidden rest spaces inside subway stations, over three weeks.