Dev notes on AWS, JVM, Kubernetes, Spring and more.https://hello-world-log.com/https://hello-world-log.com/en/jvm-concurrency-model-8-conclusion-decision-framework/https://hello-world-log.com/en/jvm-concurrency-model-8-conclusion-decision-framework/The final part of the JVM concurrency series. A four-question framework for choosing between Virtual Thread, Reactor, and Coroutines, plus the unique strengths of each technology and the most common misconceptions.Fri, 15 May 2026 16:02:36 GMThttps://hello-world-log.com/en/jvm-concurrency-model-7-virtual-thread/https://hello-world-log.com/en/jvm-concurrency-model-7-virtual-thread/How virtual thread mount/unmount works under the hood, how it differs from coroutine continuations, why AOP proxies just work, and the synchronized pinning trap with practical fixes.Fri, 15 May 2026 12:11:08 GMThttps://hello-world-log.com/en/jvm-concurrency-model-6-spring-coroutines/https://hello-world-log.com/en/jvm-concurrency-model-6-spring-coroutines/How Spring wraps suspend fun in mono {} to run it on the Reactor pipeline, and the structural limit where AOP proxies mistake COROUTINE_SUSPENDED for method completion — including why @Transactional + coroutines does not work.Mon, 20 Apr 2026 09:23:57 GMThttps://hello-world-log.com/en/jvm-concurrency-model-5-kotlin-coroutines/https://hello-world-log.com/en/jvm-concurrency-model-5-kotlin-coroutines/Writing Reactor-style deep flatMap chains as sequential, synchronous-looking code with Kotlin Coroutines. Covers suspend, CPS transformation, state machines, Flow, Channel, and structured concurrency.Sat, 21 Mar 2026 12:18:17 GMThttps://hello-world-log.com/en/jvm-concurrency-model-4-spring-webflux/https://hello-world-log.com/en/jvm-concurrency-model-4-spring-webflux/Starting from the one-request-one-thread limit of Spring MVC, this post digs into how WebFlux actually works — the Netty event loop architecture, MVC vs WebFlux request handling, and what you must never do on an event loop thread.Sun, 15 Mar 2026 08:09:24 GMThttps://hello-world-log.com/en/jvm-concurrency-model-3-reactive-streams-reactor/https://hello-world-log.com/en/jvm-concurrency-model-3-reactive-streams-reactor/From the Pull vs Push model to the four Reactive Streams interfaces, Reactor's Mono/Flux and core operators, and backpressure — building a solid mental model of reactive programming.Sun, 08 Mar 2026 09:33:02 GMThttps://hello-world-log.com/en/jvm-concurrency-model-2-java-traditional-concurrency/https://hello-world-log.com/en/jvm-concurrency-model-2-java-traditional-concurrency/From Thread and Runnable to Callable/Future, ExecutorService, and CompletableFuture — tracing how Java's concurrency API evolved toward "stop managing threads yourself."Tue, 03 Mar 2026 14:30:48 GMThttps://hello-world-log.com/en/jvm-concurrency-model-1-fundamentals/https://hello-world-log.com/en/jvm-concurrency-model-1-fundamentals/The difference between processes and threads, concurrency vs parallelism, and why synchronous/asynchronous and blocking/non-blocking are two independent axes — foundational concepts for the JVM concurrency series.Sat, 28 Feb 2026 08:16:47 GMThttps://hello-world-log.com/en/tracing-5-java-agent-vs-library-instrumentation/https://hello-world-log.com/en/tracing-5-java-agent-vs-library-instrumentation/Comparing how the Micrometer (library) approach and the OTel Java Agent (bytecode manipulation) approach work — a look inside premain, the Instrumentation API, and ByteBuddy code injection.Thu, 19 Feb 2026 08:05:01 GMThttps://hello-world-log.com/en/tracing-4-kotlin-coroutine-context-propagation/https://hello-world-log.com/en/tracing-4-kotlin-coroutine-context-propagation/How to propagate context in coroutines, where the thread can change at every suspend point — the structure of CoroutineContext, ThreadContextElement, and bridging ThreadLocal with asContextElement().Fri, 13 Feb 2026 10:14:59 GMThttps://hello-world-log.com/en/tracing-3-reactor-context-webflux/https://hello-world-log.com/en/tracing-3-reactor-context-webflux/Why ThreadLocal-based traceId propagation fails on the WebFlux event loop, and how Reactor Context's bottom-up propagation model solves it — with hands-on examples.Sun, 08 Feb 2026 11:28:09 GMThttps://hello-world-log.com/en/tracing-2-threadlocal-mdc/https://hello-world-log.com/en/tracing-2-threadlocal-mdc/How ThreadLocal works under the hood, how MDC gets traceId into your logs, and the moments Spring MVC actually switches threads — the fundamentals you need before going async.Sat, 07 Feb 2026 11:33:34 GMThttps://hello-world-log.com/en/tracing-1-observability-spring-otel/https://hello-world-log.com/en/tracing-1-observability-spring-otel/Why the three pillars of observability need distributed tracing, the history from Zipkin B3 through the OpenTracing/OpenCensus split to the OpenTelemetry merger, and where the Spring ecosystem stands today.Sat, 07 Feb 2026 11:26:31 GMThttps://hello-world-log.com/en/kubernetes-pod-storage-pv-pvc-2/https://hello-world-log.com/en/kubernetes-pod-storage-pv-pvc-2/What the three AccessModes really mean, the Deployment + RWO PVC trap, the PV lifecycle and Reclaim Policy — the problems you actually run into when operating PV/PVC.Mon, 12 Jan 2026 10:01:00 GMThttps://hello-world-log.com/en/kubernetes-pod-storage-pv-pvc-1/https://hello-world-log.com/en/kubernetes-pod-storage-pv-pvc-1/From the Kubernetes volume concept and Volume types like emptyDir and hostPath, to the PV/PVC architecture that decouples storage from the Pod lifecycle — the first post in the storage series.Sun, 11 Jan 2026 10:56:00 GMThttps://hello-world-log.com/en/kubernetes-computing-pod-lifecycle/https://hello-world-log.com/en/kubernetes-computing-pod-lifecycle/From kubectl apply to a running container — tracing step by step how the API Server, Controller Manager, Scheduler, and kubelet each play their part in placing and running a Pod.Sat, 10 Jan 2026 10:54:00 GMThttps://hello-world-log.com/en/kubernetes-network-guide-2-pod-to-pod/https://hello-world-log.com/en/kubernetes-network-guide-2-pod-to-pod/Who assigns Pod IPs, and how do Pods talk to each other? Following the packet flow through CNI, veth pairs, the Linux bridge, cross-node routing, and CoreDNS service discovery.Fri, 09 Jan 2026 11:01:00 GMThttps://hello-world-log.com/en/kubernetes-network-guide-1-external-to-pod/https://hello-world-log.com/en/kubernetes-network-guide-1-external-to-pod/Tracing the full path of an external HTTP request through LB → Ingress Controller → Service → Pod — covering kube-proxy and iptables, conntrack, and troubleshooting commands for every hop.Thu, 08 Jan 2026 11:00:00 GMThttps://hello-world-log.com/en/aws-ec2-cloudwatch-dashboard-logs-monitoring-3/https://hello-world-log.com/en/aws-ec2-cloudwatch-dashboard-logs-monitoring-3/How to bring CPU, memory, disk, and network metrics together on a single CloudWatch dashboard, then collect server logs and connect alarms to complete your EC2 monitoring setup.Tue, 06 Jan 2026 13:36:55 GMThttps://hello-world-log.com/en/aws-ec2-cloudwatch-agent-memory-disk-monitoring-2/https://hello-world-log.com/en/aws-ec2-cloudwatch-agent-memory-disk-monitoring-2/How to collect the memory and disk metrics that EC2 basic monitoring leaves out, using the CloudWatch Agent. Step-by-step coverage from creating the IAM role to installing and configuring the agent, plus its resource overhead on a t3.micro.Tue, 06 Jan 2026 13:32:45 GMThttps://hello-world-log.com/en/aws-ec2-monitoring-cloudwatch-guide-1/https://hello-world-log.com/en/aws-ec2-monitoring-cloudwatch-guide-1/How the EC2 monitoring tab relates to CloudWatch, basic vs. detailed monitoring costs, and what the free tier covers — part one of a series on monitoring EC2 server health.Tue, 06 Jan 2026 13:22:22 GMThttps://hello-world-log.com/en/spring-webflux-netty-dns-apple-silicon-fix/https://hello-world-log.com/en/spring-webflux-netty-dns-apple-silicon-fix/Why Spring Cloud Gateway alone fails DNS resolution on Apple Silicon Macs (Netty's own DNS resolver) and how to fix it — plus a look at native library dependencies and Gradle Configuration concepts.Sun, 04 Jan 2026 07:43:48 GMThttps://hello-world-log.com/en/spring-one-indexed-parameters-pageable-default/https://hello-world-log.com/en/spring-one-indexed-parameters-pageable-default/Enable one-indexed-parameters and @PageableDefault(page = 1) suddenly points at the second page — tracing the cause through the Spring Data source code and tests, and pinning down the correct usage.Sat, 03 Jan 2026 08:06:46 GMThttps://hello-world-log.com/en/aws-ec2-ebs-volume-expansion-guide/https://hello-world-log.com/en/aws-ec2-ebs-volume-expansion-guide/How to expand an EBS volume on a full EC2 instance with zero downtime — diagnosing disk usage, emergency cleanup with docker system prune, and applying the new size with growpart and resize2fs.Fri, 02 Jan 2026 04:50:07 GMThttps://hello-world-log.com/en/gapyeong-petite-france-review/https://hello-world-log.com/en/gapyeong-petite-france-review/A visit to Petite France in Gapyeong, an hour from Seoul. The Little Prince exhibits, K-drama filming locations, a European antique collection, and the Italian village next door — with tickets, hours, and directions.Sun, 28 Dec 2025 06:37:02 GMThttps://hello-world-log.com/en/walkerhill-douglas-house-christmas-review/https://hello-world-log.com/en/walkerhill-douglas-house-christmas-review/One night over Christmas at Walkerhill Douglas House, a 1963 Kim Swoo-geun building in eastern Seoul. The room, the lounge, breakfast over the Han River, and what it costs.Sat, 27 Dec 2025 12:20:55 GMThttps://hello-world-log.com/en/aws-wordpress-blog-setup-docker-cloudflare/https://hello-world-log.com/en/aws-wordpress-blog-setup-docker-cloudflare/The full walkthrough of running WordPress on AWS EC2 with Docker Compose and wiring up a domain and HTTPS through Cloudflare — SSH config, Security Groups, and Elastic IP, written for first-time server builders.Sat, 06 Dec 2025 06:48:02 GMT