The site of Yosuke Maruyama, a software engineer based in Tokyo. Selected API design and implementation work with Python and TypeScript, plus technical articles.https://yomaru-tech.com/enhttps://yomaru-tech.com/en/posts/inhouse-vs-outsourcing/https://yomaru-tech.com/en/posts/inhouse-vs-outsourcing/AI and IaC have made writing code much easier, yet even a small change can still mean quotes, approvals, and a contract with an outside vendor. That is the norm in Japan, where most IT engineers work at vendors rather than at the companies that use the systems. This post sorts out seven situations where you could build it in-house but have to outsource anyway, when outsourcing is the right call, and how to work your way out.Thu, 01 Oct 2026 00:00:00 GMTengineeringarchitecturehttps://yomaru-tech.com/en/posts/office-for-decision-phase/https://yomaru-tech.com/en/posts/office-for-decision-phase/Coming into the office has real costs, but when a team is deciding on requirements and design, being in the same room gives it an edge. Splitting development into a "deciding" phase and a "building" phase, I lay out how to use office days well.Wed, 30 Sep 2026 00:00:00 GMTcareerengineeringhttps://yomaru-tech.com/en/posts/redis-sorted-set-lua-matching/https://yomaru-tech.com/en/posts/redis-sorted-set-lua-matching/The matching side of an anonymous chat app, which puts people who picked the same topic into rooms of two or three. The waiting queue is a Redis sorted set, and taking people off it is a single Lua script, so no one gets assigned twice even when both servers try at the same moment.Sun, 27 Sep 2026 00:00:00 GMTredisgohttps://yomaru-tech.com/en/posts/iac-for-cloud-beginners/https://yomaru-tech.com/en/posts/iac-for-cloud-beginners/If you have plenty of on-prem infrastructure experience but are new to both the cloud and IaC, this post explains how IaC differs from building by hand in the console, why you should use it, and which tool to pick.Sat, 26 Sep 2026 00:00:00 GMTiacterraformawsazuregcphttps://yomaru-tech.com/en/posts/pubsub-vs-queue/https://yomaru-tech.com/en/posts/pubsub-vs-queue/Both decouple producers from consumers, but they differ in who a message goes to and how many receive it. A queue splits up work; Pub/Sub shares what happened. This post covers how to combine them, an AWS example, and the design pitfalls to watch for.Sat, 26 Sep 2026 00:00:00 GMTarchitectureawshttps://yomaru-tech.com/en/posts/crawler-and-seo/https://yomaru-tech.com/en/posts/crawler-and-seo/The crawler and SEO part I skipped over in the previous post on CSR, SSR and SSG. How a search engine goes from finding a page to listing it in results, and how to write HTML that tends to rank well.Thu, 24 Sep 2026 00:00:00 GMTseorenderinghttps://yomaru-tech.com/en/posts/typesafe-jev-system-one-model/https://yomaru-tech.com/en/posts/typesafe-jev-system-one-model/TypeSafe AI's Jev, released in September 2026, returns typed decisions instead of text. How it differs from generative LLMs, where it fits inside a system, the local-compatible jeff, and how to judge production readiness today.Wed, 23 Sep 2026 00:00:00 GMTaiarchitecturehttps://yomaru-tech.com/en/posts/shamir-lagrange/https://yomaru-tech.com/en/posts/shamir-lagrange/Shamir's secret sharing rests its security on one mathematical fact — a polynomial is uniquely determined by k points. Here I follow, with formulas and concrete numbers, where Lagrange interpolation comes into play.Tue, 22 Sep 2026 00:00:00 GMTsecurityalgorithmhttps://yomaru-tech.com/en/posts/why-secure-computation-and-secret-sharing/https://yomaru-tech.com/en/posts/why-secure-computation-and-secret-sharing/Using data you cannot let out of the building, without moving the raw records. Here I follow the mechanism with actual numbers, then work through why these techniques are wanted now — market forecasts, regulation, and deployments that already exist.Mon, 21 Sep 2026 00:00:00 GMTsecurityaihttps://yomaru-tech.com/en/posts/why-conformity-kills-focus/https://yomaru-tech.com/en/posts/why-conformity-kills-focus/Managed homework in high school, an identical university curriculum, and a first job running through runbooks. I had filed these away as separate experiences, but looking back they share one mechanism. Here I line up social loafing, self-determination theory, and the Job Characteristics Model along one axis — sense of agency.Sun, 20 Sep 2026 00:00:00 GMTcareerengineeringhttps://yomaru-tech.com/en/posts/rural-urban-information-and-the-brain/https://yomaru-tech.com/en/posts/rural-urban-information-and-the-brain/Two years after moving from Okayama to Tokyo. Too little stimulation in the countryside and too much information in the city are both a cost to cognition. Working from the research, here is why this is a question about how you handle information rather than where you live.Sat, 19 Sep 2026 00:00:00 GMTcareerengineeringhttps://yomaru-tech.com/en/posts/modular-monolith-vs-layered/https://yomaru-tech.com/en/posts/modular-monolith-vs-layered/Modular monolith and layered architecture are not alternatives you pick between; they nest inside each other at different granularities. Working from the actual structure of my own code, here is why Go's package boundaries only protect the walls along the feature axis.Thu, 17 Sep 2026 00:00:00 GMTgoarchitecturehttps://yomaru-tech.com/en/posts/travel-work-fundamentals/https://yomaru-tech.com/en/posts/travel-work-fundamentals/Adapting to unfamiliar environments, valuing first-hand information, breaking a trip into tasks ahead of time — the small things we do while traveling quietly train the fundamentals of work. Drawing on my own experience as a software engineer, here are eight overlaps that apply to anyone with a job.Mon, 14 Sep 2026 00:00:00 GMTcareerengineeringhttps://yomaru-tech.com/en/posts/recursion-advanced-3months/https://yomaru-tech.com/en/posts/recursion-advanced-3months/Three months on from Recursion's computer science fundamentals course. Why I changed my mind about needing to write code by hand in an age of AI, split into resolution, complexity, and how it plays out at work.Tue, 08 Sep 2026 00:00:00 GMTalgorithmengineeringhttps://yomaru-tech.com/en/posts/csr-ssr-ssg/https://yomaru-tech.com/en/posts/csr-ssr-ssg/One axis — browser, server, or build time — is enough to sort out CSR, SSR and SSG. With a screen-by-screen example from an anonymous chat service.Sun, 06 Sep 2026 00:00:00 GMTrenderingastrohttps://yomaru-tech.com/en/posts/websocket-vs-http-for-chat/https://yomaru-tech.com/en/posts/websocket-vs-http-for-chat/Starting from why messages arrive instantly, through to the implementation (Go / gorilla/websocket / Redis Pub/Sub) behind an anonymous chat app. Diagrams of the difference between HTTP and WebSocket.Fri, 04 Sep 2026 00:00:00 GMTwebsocketgohttps://yomaru-tech.com/en/posts/free-observability-on-a-tight-budget/https://yomaru-tech.com/en/posts/free-observability-on-a-tight-budget/The infrastructure budget is already spent. Here is how I split what I wanted to watch into three layers and covered all of it with CloudWatch, Performance Insights, and Grafana Cloud Free.Thu, 03 Sep 2026 00:00:00 GMTawsgrafanahttps://yomaru-tech.com/en/posts/go-goroutines-vs-node-event-loop/https://yomaru-tech.com/en/posts/go-goroutines-vs-node-event-loop/Not because it won on performance. With at most three people in a room, here is where Go and Node.js actually differed.Mon, 31 Aug 2026 00:00:00 GMTgonodejshttps://yomaru-tech.com/en/posts/why-astro-vercel-cloudflare/https://yomaru-tech.com/en/posts/why-astro-vercel-cloudflare/A custom domain, HTTPS, a contact form and inbound mail — without renting a single server. What I picked, and what I turned down.Tue, 25 Aug 2026 00:00:00 GMTastrovercelcloudflarehttps://yomaru-tech.com/en/posts/lambda-json-logger/https://yomaru-tech.com/en/posts/lambda-json-logger/Emitting one JSON object per line so CloudWatch Logs Insights can filter on fields directly.Sat, 15 Aug 2026 00:00:00 GMTawspython