https://jun0.dev/blog Junyoung Yang ko y@jun0.dev (Junyoung Yang) y@jun0.dev (Junyoung Yang) Wed, 06 May 2026 00:00:00 GMT https://jun0.dev/blog/ollama-to-vllm-serving https://jun0.dev/blog/ollama-to-vllm-serving Ollama 기반 LLM 서버의 동시 요청 병목을 분석하고 vLLM으로 전환해 동시 사용자 50명 수준까지 안정적으로 처리하도록 개선했습니다. Wed, 06 May 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) 대표글llmvllmkubernetesinfra https://jun0.dev/blog/ollama-to-vllm-serving https://jun0.dev/blog/ollama-to-vllm-serving I analyzed the performance bottlenecks that appeared when concurrent requests increased on an Ollama-based LLM server, then moved the serving layer to vLLM so it could stably handle around 50 concurrent users. Wed, 06 May 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) 대표글llmvllmkubernetesinfra https://jun0.dev/blog/k3s-vllm-gpu-workload https://jun0.dev/blog/k3s-vllm-gpu-workload Code Place AI 조교 기능을 운영 클러스터에서 실행하기 위해 NVIDIA 드라이버, runtime, k3s containerd, RuntimeClass, device plugin 설정을 맞췄습니다. Sat, 02 May 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) 대표글kubernetesk3svllmcudainfra https://jun0.dev/blog/k3s-vllm-gpu-workload https://jun0.dev/blog/k3s-vllm-gpu-workload Setting up the NVIDIA driver, runtime, k3s containerd, RuntimeClass, and device plugin needed to run the Code Place AI assistant on an operations cluster. Sat, 02 May 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) 대표글kubernetesk3svllmcudainfra https://jun0.dev/blog/longhorn-cnpg-troubleshooting https://jun0.dev/blog/longhorn-cnpg-troubleshooting Code Place 운영 중 WAL 증가로 시작된 디스크 부족 장애를 Longhorn replica 조정, CNPG 복구, multipathd 간섭 해결, 디스크 추가, WAL 상태 점검으로 복구했습니다. Mon, 27 Apr 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) 대표글kuberneteslonghorncnpgpostgresqlinfra https://jun0.dev/blog/longhorn-cnpg-troubleshooting https://jun0.dev/blog/longhorn-cnpg-troubleshooting Recovering a Code Place disk pressure failure that started with WAL growth by adjusting Longhorn replicas, restoring CNPG, resolving multipathd interference, adding disk space, and checking WAL state afterward. Mon, 27 Apr 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) 대표글kuberneteslonghorncnpgpostgresqlinfra https://jun0.dev/blog/longhorn-mount-conflict-multipathd https://jun0.dev/blog/longhorn-mount-conflict-multipathd WAL 폭주 이후 Longhorn·CNPG 복구 과정에서 발생한 볼륨 마운트 실패를 Kubernetes 이벤트, share-manager, ext4 메시지, multipathd 간섭 가능성으로 추적했습니다. Thu, 23 Apr 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) 대표글longhornkuberneteslinuxstorageinfra https://jun0.dev/blog/longhorn-mount-conflict-multipathd https://jun0.dev/blog/longhorn-mount-conflict-multipathd Tracing a Longhorn volume mount failure after WAL growth through Kubernetes events, share-manager state, ext4 messages, and possible multipathd interference. Thu, 23 Apr 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) 대표글longhornkuberneteslinuxstorageinfra https://jun0.dev/blog/grit-livekit-senddata-events https://jun0.dev/blog/grit-livekit-senddata-events GRIT 실시간 화상 스터디 플랫폼에서 LiveKit SendData로 이모지 리액션과 포모도로 타이머 상태를 방 안에 전달하는 구조를 설계했습니다. Tue, 14 Apr 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) spring-bootlivekitwebrtcrealtime https://jun0.dev/blog/grit-livekit-senddata-events https://jun0.dev/blog/grit-livekit-senddata-events Using LiveKit SendData in GRIT to deliver emoji reactions and Pomodoro timer state inside a real-time video study room. Tue, 14 Apr 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) spring-bootlivekitwebrtcrealtime https://jun0.dev/blog/spring-security-filter-exception-handling https://jun0.dev/blog/spring-security-filter-exception-handling GRIT의 JWT 인증 필터 에러가 공통 응답이 아니라 Tomcat 500으로 내려오던 문제를 기준으로 Spring Security 필터 예외 처리 흐름을 정리했습니다. Thu, 09 Apr 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) 대표글spring-securityjwtspring-bootbackend https://jun0.dev/blog/spring-security-filter-exception-handling https://jun0.dev/blog/spring-security-filter-exception-handling Tracing why JWT authentication filter errors in GRIT bypassed the common API response and handling them at the correct Spring Security layer. Thu, 09 Apr 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) 대표글spring-securityjwtspring-bootbackend https://jun0.dev/blog/entity-validation-refactoring https://jun0.dev/blog/entity-validation-refactoring GRIT 사용자 프로필 초기화·수정 로직에서 반복되던 검증과 대입 흐름을 엔티티 내부 규칙으로 정리했습니다. Fri, 06 Mar 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) javarefactoringvalidationdomain-modelbackend https://jun0.dev/blog/entity-validation-refactoring https://jun0.dev/blog/entity-validation-refactoring Moving repeated validation and assignment logic in GRIT's user profile flow into entity-level rules. Fri, 06 Mar 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) javarefactoringvalidationdomain-modelbackend https://jun0.dev/blog/grit-observability-prometheus-loki-grafana https://jun0.dev/blog/grit-observability-prometheus-loki-grafana GRIT 운영 준비를 위해 Spring Actuator, Prometheus, Loki, Grafana로 메트릭과 로그를 수집하고 확인할 수 있는 기본 모니터링 구성을 만들었습니다. Thu, 19 Feb 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) spring-bootprometheuslokigrafanamonitoring https://jun0.dev/blog/grit-observability-prometheus-loki-grafana https://jun0.dev/blog/grit-observability-prometheus-loki-grafana Preparing GRIT operations by collecting and checking metrics and logs with Spring Actuator, Prometheus, Loki, and Grafana. Thu, 19 Feb 2026 00:00:00 GMT y@jun0.dev (Junyoung Yang) spring-bootprometheuslokigrafanamonitoring https://jun0.dev/blog/timetable-ai-recognition https://jun0.dev/blog/timetable-ai-recognition UniSchedule에서 시간표 이미지를 일정 데이터로 변환하기 위해 GPT Vision과 Structured Output을 사용하고 프롬프트를 개선했습니다. Mon, 27 Oct 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) aiprompt-engineeringstructured-outputbackend https://jun0.dev/blog/timetable-ai-recognition https://jun0.dev/blog/timetable-ai-recognition Using GPT Vision and Structured Output in UniSchedule to convert timetable images into schedule data and improve prompt reliability. Mon, 27 Oct 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) aiprompt-engineeringstructured-outputbackend https://jun0.dev/blog/unischedule-redis-pubsub-schedule-events https://jun0.dev/blog/unischedule-redis-pubsub-schedule-events UniSchedule의 멀티 인스턴스 환경에서 일부 사용자에게 채팅 메시지가 전달되지 않던 문제를 Redis Pub/Sub으로 해결했습니다. Tue, 14 Oct 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) 대표글spring-bootredispubsubawsarchitecture https://jun0.dev/blog/unischedule-redis-pubsub-schedule-events https://jun0.dev/blog/unischedule-redis-pubsub-schedule-events Using Redis Pub/Sub in UniSchedule to deliver chat messages reliably across multiple application instances. Tue, 14 Oct 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) 대표글spring-bootredispubsubawsarchitecture https://jun0.dev/blog/webclient-vs-resttemplate https://jun0.dev/blog/webclient-vs-resttemplate UniSchedule에서 외부 API를 연동하며 Spring의 공식 지원 방향, 설정 유연성, 현재 MVC 구조를 기준으로 RestTemplate과 WebClient 중 WebClient를 선택했습니다. Thu, 18 Sep 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) springwebclienthttp-clientbackend https://jun0.dev/blog/webclient-vs-resttemplate https://jun0.dev/blog/webclient-vs-resttemplate How I chose WebClient over RestTemplate in UniSchedule based on Spring's direction, configuration flexibility, and the existing MVC structure. Thu, 18 Sep 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) springwebclienthttp-clientbackend https://jun0.dev/blog/ondelete-vs-jpa-cascade https://jun0.dev/blog/ondelete-vs-jpa-cascade 상품 삭제 시 옵션까지 함께 삭제해야 하는 요구사항에서 Hibernate @OnDelete와 JPA Cascade를 비교하고 영속성 컨텍스트 일관성까지 고려했습니다. Sun, 29 Jun 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) jpahibernatecascadedatabasebackend https://jun0.dev/blog/ondelete-vs-jpa-cascade https://jun0.dev/blog/ondelete-vs-jpa-cascade How I compared Hibernate @OnDelete and JPA Cascade for deleting product options while keeping persistence context consistency in mind. Sun, 29 Jun 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) jpahibernatecascadedatabasebackend https://jun0.dev/blog/circular-reference-lazy-limit https://jun0.dev/blog/circular-reference-lazy-limit 선물하기 API 구현 중 ProductService와 OptionService의 순환 참조를 @Lazy로 덮지 않고 의존 방향과 역할 분리 관점에서 해결했습니다. Sun, 22 Jun 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) springdependency-injectionarchitecturebackend https://jun0.dev/blog/circular-reference-lazy-limit https://jun0.dev/blog/circular-reference-lazy-limit How I resolved a circular reference between ProductService and OptionService in a gift API by revisiting dependency direction instead of hiding it with @Lazy. Sun, 22 Jun 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) springdependency-injectionarchitecturebackend https://jun0.dev/blog/pageable-input-validation https://jun0.dev/blog/pageable-input-validation Spring Pageable을 그대로 노출했을 때 정렬 기준과 페이지 크기 규칙이 느슨해지는 문제를 PageRequestDto로 제어했습니다. Tue, 17 Jun 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) springpaginationvalidationapi-design https://jun0.dev/blog/pageable-input-validation https://jun0.dev/blog/pageable-input-validation Why I introduced a PageRequestDto instead of exposing Spring Pageable directly, so sort fields and page size rules could be controlled more clearly. Tue, 17 Jun 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) springpaginationvalidationapi-design https://jun0.dev/blog/pagination-count-query-cost https://jun0.dev/blog/pagination-count-query-cost 목록 조회 API에서 Page가 자동 수행하는 count 쿼리 비용을 확인하고 Page와 Slice 선택 기준을 정리했습니다. Thu, 12 Jun 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) jpapaginationspring-dataperformance https://jun0.dev/blog/pagination-count-query-cost https://jun0.dev/blog/pagination-count-query-cost How I compared Page and Slice after reviewing the cost of automatic count queries in list APIs. Thu, 12 Jun 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) jpapaginationspring-dataperformance https://jun0.dev/blog/jpa-n-plus-one-problem https://jun0.dev/blog/jpa-n-plus-one-problem 선물하기 API에서 연관 데이터 조회 시 발생할 수 있는 JPA N+1 문제를 Fetch Join, EntityGraph, Batch Size 관점에서 비교했습니다. Wed, 04 Jun 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) jpahibernatespringperformance https://jun0.dev/blog/jpa-n-plus-one-problem https://jun0.dev/blog/jpa-n-plus-one-problem A comparison of Fetch Join, EntityGraph, and Batch Size while handling related data queries in a gift API. Wed, 04 Jun 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) jpahibernatespringperformance https://jun0.dev/blog/rest-delete-body-design https://jun0.dev/blog/rest-delete-body-design 선물하기 API DELETE 요청에서 삭제 관련 값을 Body, Query Parameter, Path Variable 중 어디에 둘지 검토하고 삭제 대상을 더 명확히 표현했습니다. Thu, 29 May 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) rest-apihttpapi-designbackend https://jun0.dev/blog/rest-delete-body-design https://jun0.dev/blog/rest-delete-body-design Choosing where DELETE request values belong in a gift API and avoiding request bodies when the target can be expressed more clearly. Thu, 29 May 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) rest-apihttpapi-designbackend https://jun0.dev/blog/uuid-index-performance https://jun0.dev/blog/uuid-index-performance UUID를 식별자로 사용할 때 UUIDv4, ULID, UUIDv7이 인덱스 성능과 정렬 특성에 어떤 차이를 만드는지 비교했습니다. Fri, 23 May 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) uuiddatabaseindexperformance https://jun0.dev/blog/uuid-index-performance https://jun0.dev/blog/uuid-index-performance Comparing UUIDv4, ULID, and UUIDv7 for identifier design, index performance, and ordering behavior. Fri, 23 May 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) uuiddatabaseindexperformance https://jun0.dev/blog/attacklab-buffer-overflow-writeup https://jun0.dev/blog/attacklab-buffer-overflow-writeup Buffer Overflow 취약점을 이용해 AttackLab 5개 Phase를 해체하고 Code Injection과 ROP(Return-Oriented Programming)를 적용했습니다. Tue, 20 May 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) system-softwareassemblygdbx86buffer-overflowrop https://jun0.dev/blog/attacklab-buffer-overflow-writeup https://jun0.dev/blog/attacklab-buffer-overflow-writeup Solving the five AttackLab phases with buffer overflow, code injection, and ROP(Return-Oriented Programming). Tue, 20 May 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) system-softwareassemblygdbx86buffer-overflowrop https://jun0.dev/blog/bomblab-binary-bomb-writeup https://jun0.dev/blog/bomblab-binary-bomb-writeup 주어진 Binary 파일을 GDB로 disassembly하고 디버깅해 6개 Phase와 Secret Phase를 해체했습니다. Mon, 19 May 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) system-softwareassemblygdbx86reverse-engineering https://jun0.dev/blog/bomblab-binary-bomb-writeup https://jun0.dev/blog/bomblab-binary-bomb-writeup Defusing six BombLab phases and the secret phase by disassembling and debugging the given binary with GDB. Mon, 19 May 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) system-softwareassemblygdbx86reverse-engineering https://jun0.dev/blog/application-validation-select-update https://jun0.dev/blog/application-validation-select-update 카카오테크캠퍼스 선물하기 API에서 DB 제약조건에만 맡길지, 애플리케이션에서 먼저 검증할지 기준을 세웠습니다. Wed, 07 May 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) springjpavalidationdatabasebackend https://jun0.dev/blog/application-validation-select-update https://jun0.dev/blog/application-validation-select-update Deciding when a Kakao Tech Campus gift API should rely on database constraints and when it should validate rules in the application layer. Wed, 07 May 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) springjpavalidationdatabasebackend https://jun0.dev/blog/rag-pipeline-llm-hallucination https://jun0.dev/blog/rag-pipeline-llm-hallucination DocDoc에서 질문만 LLM에 전달할 때 생기는 근거 없는 답변을 RAG, reranking, SSE 스트리밍으로 줄였습니다. Sun, 13 Apr 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) ragllmpineconelangchainai https://jun0.dev/blog/rag-pipeline-llm-hallucination https://jun0.dev/blog/rag-pipeline-llm-hallucination Building a medical paper-based answer flow in DocDoc with RAG, reranking, and SSE streaming to reduce unsupported LLM answers. Sun, 13 Apr 2025 00:00:00 GMT y@jun0.dev (Junyoung Yang) ragllmpineconelangchainai https://jun0.dev/blog/android-fragment-savedinstancestate https://jun0.dev/blog/android-fragment-savedinstancestate Android 편의 앱에서 백그라운드 복귀 후 Fragment 표시 상태가 깨지던 문제를 savedInstanceState와 생명주기 흐름으로 해결했습니다. Sun, 22 Mar 2020 00:00:00 GMT y@jun0.dev (Junyoung Yang) androidfragmentlifecycledebuggingearly-project https://jun0.dev/blog/android-fragment-savedinstancestate https://jun0.dev/blog/android-fragment-savedinstancestate Fixing an Android Fragment display issue after background return by tracing savedInstanceState and lifecycle behavior. Sun, 22 Mar 2020 00:00:00 GMT y@jun0.dev (Junyoung Yang) androidfragmentlifecycledebuggingearly-project https://jun0.dev/blog/iot-tcp-socket-lighting https://jun0.dev/blog/iot-tcp-socket-lighting IoT 자율형 전등 프로젝트에서 NodeMCU와 Android 앱 사이의 상태를 실시간으로 주고받기 위해 HTTP polling 대신 TCP 소켓 서버를 만들었습니다. Fri, 18 Oct 2019 00:00:00 GMT y@jun0.dev (Junyoung Yang) nodejstcpsocketiotearly-project https://jun0.dev/blog/iot-tcp-socket-lighting https://jun0.dev/blog/iot-tcp-socket-lighting Building a TCP socket server for an autonomous IoT lamp so a NodeMCU device and Android app could exchange state updates in real time without HTTP polling. Fri, 18 Oct 2019 00:00:00 GMT y@jun0.dev (Junyoung Yang) nodejstcpsocketiotearly-project