@startuml test-simple
!theme mono

title User Service - 회원가입 내부 시퀀스

participant "UserController" as Controller <<API Layer>>
participant "Redis Cache" as Redis <<E>>
participant "User DB (PostgreSQL)" as UserDB <<E>>

actor Client
Client -> Controller: POST /api/users/register
activate Controller

Controller -> Controller: validate input

alt 중복 사용자 존재
    Controller --> Client: 400 Bad Request
    deactivate Controller
else 신규 사용자
    Controller --> Client: 201 Created
    deactivate Controller
end

@enduml