Jaehong Jung's personal bloghttps://jaehong21.com/https://jaehong21.com/posts/answer-why-cpu-throttling/https://jaehong21.com/posts/answer-why-cpu-throttling/A short piece about reading the hidden intent behind the simple question "Why does a CPU throttle?"Wed, 15 Apr 2026 00:00:00 GMThttps://jaehong21.com/posts/channel-io-istio-ambient-02/https://jaehong21.com/posts/channel-io-istio-ambient-02/A deep dive into how Istio Ambient mode's HBONE tunneling and traffic redirection are implemented in Envoy configs.Tue, 14 Apr 2026 00:00:00 GMThttps://jaehong21.com/posts/channel-io-istio-ambient-01/https://jaehong21.com/posts/channel-io-istio-ambient-01/Introduction to why Channel.io's DevOps team chose Istio Ambient mode and how it works.Fri, 20 Mar 2026 00:00:00 GMThttps://jaehong21.com/posts/istio-ext-authz-envoy-config/https://jaehong21.com/posts/istio-ext-authz-envoy-config/Analyzing how Istio AuthorizationPolicy's action: CUSTOM works in Envoy config based on actual envoy config dump.Tue, 10 Mar 2026 00:00:00 GMThttps://jaehong21.com/posts/python-async-blocking-probe/https://jaehong21.com/posts/python-async-blocking-probe/How calling a CPU-bound sync function inside an async endpoint blocked /v1/healthTue, 17 Feb 2026 00:00:00 GMThttps://jaehong21.com/posts/httproute-regex-path-matching/https://jaehong21.com/posts/httproute-regex-path-matching/Deep dive into Istio's HTTPRoute path matching priority and why PathPrefix always wins over RegularExpressionTue, 15 Jul 2025 00:00:00 GMThttps://jaehong21.com/posts/istio-client-ip-proxy-protocol/https://jaehong21.com/posts/istio-client-ip-proxy-protocol/How to obtain the real client IP in an AWS NLB + Istio Gateway environment where even numTrustedProxies doesn't help, solved with Proxy Protocol v2.Wed, 02 Apr 2025 00:00:00 GMThttps://jaehong21.com/posts/channel-io-gha-arc-02/https://jaehong21.com/posts/channel-io-gha-arc-02/Case studies and lessons learned from operating and troubleshooting the Kubernetes Actions Runner Controller (ARC) at Channel.io.Wed, 19 Mar 2025 00:00:00 GMThttps://jaehong21.com/posts/channel-io-gha-arc-01/https://jaehong21.com/posts/channel-io-gha-arc-01/A story about how Channel.io moved from CircleCI to GitHub Actions with self-hosted runners.Tue, 18 Mar 2025 00:00:00 GMThttps://jaehong21.com/posts/retrospect-2024-09/https://jaehong21.com/posts/retrospect-2024-09/3 months passed by in the blink of an eye. Repeating my daily routine of work and development at home, there were no major events, but when I look back, it was quite a busy 90 days after all.Mon, 30 Sep 2024 00:00:00 GMThttps://jaehong21.com/posts/uptimeninja-redis-stream/https://jaehong21.com/posts/uptimeninja-redis-stream/I am conceptualizing an event-driven architecture using Redis Streams for the Uptimeninja.io service. Along the way, I've encountered several challenges related to scaling out producers and consumers.Sun, 28 Jul 2024 00:00:00 GMThttps://jaehong21.com/posts/retrospect-2024-06/https://jaehong21.com/posts/retrospect-2024-06/I can confidently say that over the past 3 months, I've been sitting in front of a computer except for eating and sleeping. But I enjoyed every moment of it. I was obsessed with development 1) while at work, and 2) even on weekends.Sun, 30 Jun 2024 00:00:00 GMThttps://jaehong21.com/posts/ubuntu-install/https://jaehong21.com/posts/ubuntu-install/Complete guide to install vanilla Kubernetes on Ubuntu machines using kubeadm. Also providing ways to operate Nvidia GPU nodes on kubernetes.Sat, 11 May 2024 00:00:00 GMThttps://jaehong21.com/posts/java-jdeps-jlink/https://jaehong21.com/posts/java-jdeps-jlink/Learn to drastically cut Java Docker image sizes using jdeps and jlink for creating custom Java Runtime EnvironmentMon, 08 Apr 2024 00:00:00 GMThttps://jaehong21.com/posts/arch-linux-01-install/https://jaehong21.com/posts/arch-linux-01-install/This article goes through the complete process of installing Arch Linux, including disk partitioning, encryption, configuring LVM and grub. Furthermore, setting up essential packages and services.Sat, 16 Mar 2024 00:00:00 GMThttps://jaehong21.com/posts/arch-linux-install/https://jaehong21.com/posts/arch-linux-install/Complete guide to install vanilla Kubernetes on Arch Linux machines using kubeadm.Thu, 14 Mar 2024 00:00:00 GMThttps://jaehong21.com/posts/k3s-06-sealed-secrets/https://jaehong21.com/posts/k3s-06-sealed-secrets/Kubernetes secrets are not actually safe to store on git. it is just base64 encoded. sealed secrets are encrypted with a key pair.Thu, 21 Dec 2023 00:00:00 GMThttps://jaehong21.com/posts/k3s-05-https-certificate/https://jaehong21.com/posts/k3s-05-https-certificate/How to attach TLS certificate to K3s ingress using let's encrypt and dns-01 challlenges. Also, how to attach TLS certificate using Cloudflare Origin CA with proxied to Cloudflare NetworkTue, 19 Dec 2023 00:00:00 GMThttps://jaehong21.com/posts/k3s-04-service-lb/https://jaehong21.com/posts/k3s-04-service-lb/How to expose K3s container service to outside using LoadBalancer. There are two options, using K3s default LoadBalancer Klipper or MetalLB which is well known for on-premise LoadBalancer.Thu, 14 Dec 2023 00:00:00 GMThttps://jaehong21.com/posts/k3s-03-docker-credentials/https://jaehong21.com/posts/k3s-03-docker-credentials/How to download docker credentials from AWS ECR and inject to K3s cluster.Sat, 09 Dec 2023 00:00:00 GMThttps://jaehong21.com/posts/k3s-02-access-outside/https://jaehong21.com/posts/k3s-02-access-outside/How to Access K3s cluster with kubectl from outside. To issue kubeconfig credential to access K3s API server.Thu, 07 Dec 2023 00:00:00 GMThttps://jaehong21.com/posts/k3s-01-install/https://jaehong21.com/posts/k3s-01-install/How to initially setup K3s cluster and setup Terraform for K3s nodes.Wed, 06 Dec 2023 00:00:00 GMThttps://jaehong21.com/posts/sparcs-wing-session/https://jaehong21.com/posts/sparcs-wing-session/SPARCS(Programmer's association from KAIST) X WING (students' developer club associated to GIST), have held an event to share each member's developer experienceSat, 16 Sep 2023 00:00:00 GMThttps://jaehong21.com/posts/gist-dev-night-2023/https://jaehong21.com/posts/gist-dev-night-2023/Speaker at GIST Developer's Night 2023, giving lecture about polyglot developer and why should you become one.Wed, 13 Sep 2023 00:00:00 GMThttps://jaehong21.com/posts/bitcoin-protocol/https://jaehong21.com/posts/bitcoin-protocol/Introducing basic steps of two different bitcoin nodes communicate at first step with some bitcoin protocol.Thu, 10 Aug 2023 00:00:00 GMThttps://jaehong21.com/posts/sudadu/https://jaehong21.com/posts/sudadu/We developed a Flutter app that recommends similar types of problems from the KSAT workbook. Deployed ML using BentoML and AWS Lambda.Tue, 13 Jun 2023 00:00:00 GMThttps://jaehong21.com/posts/gist-attendance/https://jaehong21.com/posts/gist-attendance/To solve problems on GIST campus, we created a lecture attendance app. We added GPS, Wifi network address verification, and request payload obfuscation to it.Sat, 27 May 2023 00:00:00 GMThttps://jaehong21.com/posts/wrapper-golang/https://jaehong21.com/posts/wrapper-golang/How to create custom wrapper function to inject Database object and user id from JWT and use it in each API handler.Thu, 20 Apr 2023 00:00:00 GMThttps://jaehong21.com/posts/container-without-docker/https://jaehong21.com/posts/container-without-docker/Building Container from scratch without DockerFri, 24 Mar 2023 00:00:00 GMThttps://jaehong21.com/posts/concurrent-postgres-query/https://jaehong21.com/posts/concurrent-postgres-query/Considering creating initial pool time and concurrent execution of database while building API server using Rust.Sun, 05 Mar 2023 00:00:00 GMThttps://jaehong21.com/posts/datguri/https://jaehong21.com/posts/datguri/Communicate easily with other people in same website using Chrome extension.Sun, 05 Mar 2023 00:00:00 GMThttps://jaehong21.com/posts/python-gil/https://jaehong21.com/posts/python-gil/Poor performance of python compare to other programming language is always being an issue, and this cannot be independent of GIL.Sat, 14 Jan 2023 00:00:00 GMThttps://jaehong21.com/posts/nat-instance/https://jaehong21.com/posts/nat-instance/Creating NAT instance using Terraform to access internet from private subnet.Wed, 28 Sep 2022 00:00:00 GMThttps://jaehong21.com/posts/bastion-host/https://jaehong21.com/posts/bastion-host/Divide public and private subnet using terraform and create bastion host to access private subnet.Tue, 27 Sep 2022 00:00:00 GMThttps://jaehong21.com/posts/rust-web-server/https://jaehong21.com/posts/rust-web-server/Build simple multi-thread web server using Rust's built-in TcpListener module.Wed, 14 Sep 2022 00:00:00 GMThttps://jaehong21.com/posts/c-web-server/https://jaehong21.com/posts/c-web-server/Building simple web server with socket programming using C.Tue, 13 Sep 2022 00:00:00 GMThttps://jaehong21.com/posts/socket-programming/https://jaehong21.com/posts/socket-programming/Basic concepts in OSI 7 layers and detailed interfaces and functions in socket programming.Mon, 12 Sep 2022 00:00:00 GMThttps://ml.jaehong21.com/gan/basic-informationhttps://ml.jaehong21.com/gan/basic-informationIntroduction to Generative Adversarial Networks with MNIST generation example. Written in Korean.Thu, 14 Oct 2021 00:00:00 GMThttps://ml.jaehong21.com/sequence-to-sequence/seq2seqhttps://ml.jaehong21.com/sequence-to-sequence/seq2seqIntroduction to Seq2Seq models, covering attention decoder, English-French and Korean-English translators. Written in Korean.Thu, 05 Aug 2021 00:00:00 GMThttps://ml.jaehong21.com/rnn/basic-informationhttps://ml.jaehong21.com/rnn/basic-informationFundamentals of Recurrent Neural Networks, including creating simple RNNs and sentimental classification. Written in Korean.Thu, 08 Jul 2021 00:00:00 GMThttps://ml.jaehong21.com/autoencoder-1/basic-informationhttps://ml.jaehong21.com/autoencoder-1/basic-informationIntroduction to autoencoders with Fashion MNIST example. Written in Korean.Fri, 02 Jul 2021 00:00:00 GMThttps://ml.jaehong21.com/cnn/basic-informationhttps://ml.jaehong21.com/cnn/basic-informationFundamentals of Convolutional Neural Networks, including neural network implementation, creating CNN layers, and MNIST classification. Written in Korean.Thu, 20 May 2021 00:00:00 GMThttps://ml.jaehong21.com/linear-regression/explanation-and-examplehttps://ml.jaehong21.com/linear-regression/explanation-and-exampleIntroduction to linear regression with simple Python examples and Boston house price dataset. Written in Korean.Tue, 04 May 2021 00:00:00 GMT