spring webflux: Why comming Bad Gateway error?

Question

I have a card game. As backend I have a spring boot application with webflux and RESTful API as interface. As frontend I'm using next.js application. In between is the ngnix used as a proxy.

I wanted to push some game notifications towards frontend. So I choosed server side events, but I have troubles with it. As long as more then one gamer is online, every 30-60 seconds the clients starting receving Bad Gateway errors from ngnix. After 5-10 seconds the spook is over.

As endpoint I added following method, among other endpoints

@GetMapping(path = "/events/{gamer}", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
public Flux streamFlux(@PathVariable String gamer) {
    log.info("subscribe for {}", gamer);
    return service.subscribe(gamer);
}

Then as a service I have implemented following code

final Sinks.Many sink = Sinks.many().replay().limit(20, Duration.ofMinutes(10));

@EventListener
@SneakyThrows
public void eventListener(GameEvent gameEvent) {
    log.info("occured an event {} {}", gameEvent, mapper.writeValueAsString(gameEvent));

    var event = CloudEventBuilder.v1()
            .withId(UUID.randomUUID().toString())
            .withType(gameEvent.getClass().getSimpleName())
            .withSource(URI.create("sol://some/uri"))
            .withSubject(gameEvent.getGamer())
            .withTime(OffsetDateTime.now(ZoneOffset.UTC))
            .withData ("application/json", mapper.writeValueAsString(gameEvent).getBytes(StandardCharsets.UTF_8))
            .build();

    try {
        sink.emitNext(event, Sinks.EmitFailureHandler.FAIL_FAST);
    } catch (Exception ex) {
        log.warn("Exception event emit", ex);
    }
}

public Flux subscribe(String gamer) {
    return sink.asFlux()
            .doOnNext((e) -> log.info("sent next event {}", e))
            .filter(event -> "*".equals(event.getSubject()) || event.getSubject().equals(gamer))
            .map(e -> new String(EventFormatProvider
                        .getInstance()
                        .resolveFormat(JsonFormat.CONTENT_TYPE)
                        .serialize(e))).log();
}

basicaly, I have a multicast replay sync. On some application events the event object is just wrapped to CloudEvent-object and pushed to the sync. On other end of the sync, connected clients receive only related events filtered by gamer id.

To the nginx configuration I added /api/events location. /api was already there

location /api/events {
        #limit_req zone=mylimit;
        proxy_pass http://localhost:9494;
        proxy_buffering off;
        proxy_cache off;
        proxy_set_header Connection '';
        proxy_http_version 1.1;
        chunked_transfer_encoding off;
}

location /api {
        #limit_req zone=mylimit;
        proxy_pass http://localhost:9494;
}

On UI side I do create EventSource object and listen to the incoming events.

As mentioned above, if I test it alone, everything is working almost well. But as long as some other players starting to use the game, after 30-60 seconds every request to /api/ and /api/event/ returns Bad Gateway error. In backend log I do not see any errors. It seems that webflux stops to accept connection after a while.

If I use an old version of frontend, without subscription to the the /events/{game} endpoint, the game works well. No problems. It look like the subscribe service's method is wrong.

spring webflux: Why comming Bad Gateway error?

0 Answers