https://wid-blog.github.io/en/categories/career/Recent content in Career on wid's blogHugoenSun, 31 May 2026 00:00:00 +0000https://wid-blog.github.io/en/posts/career/personal/quant-investment-platform-mid-retrospective/Sun, 31 May 2026 00:00:00 +0000https://wid-blog.github.io/en/posts/career/personal/quant-investment-platform-mid-retrospective/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.https://wid-blog.github.io/en/posts/career/dable/starting-sabbatical/Fri, 10 Apr 2026 00:00:00 +0000https://wid-blog.github.io/en/posts/career/dable/starting-sabbatical/A good engineer isn’t someone who knows technology well, but someone who can share that knowledge with their team.https://wid-blog.github.io/en/posts/career/dable/sensitive-data-encryption-retrospective/Thu, 15 Jan 2026 00:00:00 +0000https://wid-blog.github.io/en/posts/career/dable/sensitive-data-encryption-retrospective/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.https://wid-blog.github.io/en/posts/career/dable/worthy-hackathon-retrospective/Mon, 05 Jan 2026 00:00:00 +0000https://wid-blog.github.io/en/posts/career/dable/worthy-hackathon-retrospective/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.https://wid-blog.github.io/en/posts/career/dable/profitability-based-traffic-throttling/Wed, 15 Oct 2025 00:00:00 +0000https://wid-blog.github.io/en/posts/career/dable/profitability-based-traffic-throttling/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.https://wid-blog.github.io/en/posts/career/dable/dsp-fallback-ctr-ml-lifecycle/Mon, 10 Mar 2025 00:00:00 +0000https://wid-blog.github.io/en/posts/career/dable/dsp-fallback-ctr-ml-lifecycle/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.https://wid-blog.github.io/en/posts/career/dable/cascading-failure-retrospective/Thu, 13 Feb 2025 00:00:00 +0000https://wid-blog.github.io/en/posts/career/dable/cascading-failure-retrospective/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).https://wid-blog.github.io/en/posts/career/dable/campaign-cache-miss-retrospective/Wed, 27 Nov 2024 00:00:00 +0000https://wid-blog.github.io/en/posts/career/dable/campaign-cache-miss-retrospective/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.https://wid-blog.github.io/en/posts/career/personal/concurrency-go-retrospective/Wed, 03 Apr 2024 00:00:00 +0000https://wid-blog.github.io/en/posts/career/personal/concurrency-go-retrospective/A record of implementing and benchmarking three Go concurrency patterns — mutex, channel, and lock-free — to build hands-on understanding.https://wid-blog.github.io/en/posts/career/personal/chat-services-retrospective/Sun, 31 Mar 2024 00:00:00 +0000https://wid-blog.github.io/en/posts/career/personal/chat-services-retrospective/A record of designing and building a chat system as a personal project to gain hands-on experience with Kafka and Hexagonal Architecture.https://wid-blog.github.io/en/posts/career/dable/ad-fallback-server-retrospective/Wed, 28 Feb 2024 00:00:00 +0000https://wid-blog.github.io/en/posts/career/dable/ad-fallback-server-retrospective/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.https://wid-blog.github.io/en/posts/career/dable/ad-campaign-cache-optimization/Mon, 15 Jan 2024 00:00:00 +0000https://wid-blog.github.io/en/posts/career/dable/ad-campaign-cache-optimization/How I reduced network costs and enabled instance downscaling by switching from full cache refresh to incremental refresh for campaign configuration data.https://wid-blog.github.io/en/posts/career/dable/balanced-pacing-control/Mon, 21 Aug 2023 00:00:00 +0000https://wid-blog.github.io/en/posts/career/dable/balanced-pacing-control/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.https://wid-blog.github.io/en/posts/career/personal/rust-server-retrospective/Sun, 13 Mar 2022 00:00:00 +0000https://wid-blog.github.io/en/posts/career/personal/rust-server-retrospective/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.https://wid-blog.github.io/en/posts/career/startup/swapdo-startup-retrospective/Thu, 01 Jul 2021 00:00:00 +0000https://wid-blog.github.io/en/posts/career/startup/swapdo-startup-retrospective/SwapDo, a deepfake-based face synthesis meme service. A record of five months as a developer and team lead in a startup team.https://wid-blog.github.io/en/posts/career/startup/55l-ggs-startup-retrospective/Sat, 13 Mar 2021 00:00:00 +0000https://wid-blog.github.io/en/posts/career/startup/55l-ggs-startup-retrospective/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.https://wid-blog.github.io/en/posts/career/hackathon/gdg-korea-android-11-hackathon/Sat, 29 Aug 2020 00:00:00 +0000https://wid-blog.github.io/en/posts/career/hackathon/gdg-korea-android-11-hackathon/Entering the GDG Korea Android 11 Hackathon solo, building both server and app in three weeks.https://wid-blog.github.io/en/posts/career/hackathon/kric-station-public-data-hackathon/Fri, 31 Jul 2020 00:00:00 +0000https://wid-blog.github.io/en/posts/career/hackathon/kric-station-public-data-hackathon/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.