• WebSocket과 유사한 효과를 낼 수 있는 방식
• Spring WebFlux 사용시 더 깔끔하다.

• Ngnix 같은 reverse proxy 사용시에 buffering 을 끄는 등의 별도 설정이 필요하다.

• For Server-Sent Events (SSE) what Nginx proxy configuration is appropriate? - Server Fault
• wandenberg/nginx-push-stream-module: A pure stream http push technology for your Nginx setup. Comet made easy and really scalable.
• 서버측에서 X-Accel-Buffering: no 응답 헤더를 내려주면 SSE 커넥션만 버퍼링 방지.
• nginx x-accel-* 헤더를 통한 응답 제어

@RequestMapping("/sseExamples")
public SseEmitter getRealTimeJudgeResultAction(HttpServletResponse response) throws IOException {
    // ....
    response.addHeader("X-Accel-Buffering", "no");
    SseEmitter sseEmitter = new SseEmitter();
    // ....
    sseEmitter.send("Established");
    return sseEmitter;
}

# 응답 결과를 보면 X-Accel-Buffering: no 헤더가 출력됨.
curl -D - http://....
HTTP/1.1 200
X-Accel-Buffering: no
Content-Type: text/event-stream
Transfer-Encoding: chunked
...

• nginx 의 SSE 관련 url 프록시에 대해서만 proxy_buffering off; 및 기타 설정.
• ruby - EventSource / Server-Sent Events through Nginx - Stack Overflow - https://stackoverflow.com/a/13673298/1051402

location /path/to/sse {
  proxy_pass http://upstream;
  proxy_buffering off; # X-Accel-Buffering: no 와 같은 효과
  proxy_cache off;
  proxy_set_header Host $host;
  proxy_set_header Connection '';
  proxy_http_version 1.1;
  chunked_transfer_encoding off;
}

• Server Sent Events. File Upload Progress API using Server… | by Somesh Singh | Tokopedia Engineering | Medium : 좀 더 잘 설명돼 있는 듯.

• Spring5에서 HTTP Streaming | 기록은 재산이다
• Spring MVC - HTTP Streaming using ResponseBodyEmitter
• Processing streaming data with Spring WebFlux – Nithin Mallya – Medium
• Spring MVC Streaming and SSE Request Processing | Baeldung
• Server-Sent Events in Spring | Baeldung
• Event Streaming Using Spring WebFlux - DZone Java