Increasing connection timeout for Tomcat in Spring Boot

Question

How can timeout be increased so that till response is processed, request does not timeout?

Tomcat settings in Spring Boot:

server.tomcat.max-connections=2000
server.tomcat.max-threads=200
server.connection-timeout=1200000

Request per second were raised constantUsersPerSec(20) during (15) to 300 during course of 15 seconds and all requests were served as can be seen in plot below from gatling(blue).

scn.inject(
      constantUsersPerSec(20) during (15), 
    )

This is due to max-connections = 2000 which served 300 requests using 200 worker threads.

Controller is written in Spring MVC which returns DeferredResult which does asynchronous request processing and therefore will resume response once response is processed.

But even though server.connection-timeout is set to high number 1200000 there are lot of 503 towards end (red)

> status.find.in(200,304,201,202,203,204,205,206,207,208,209), b     78 (100.0%)
ut actually found 503

Gatling.conf is also set for increased timeout:

   timeOut {
      simulation = 8640000 # Absolute timeout, in seconds, of a simulation
    }
    ahc {
      #keepAlive = true                                # Allow pooling HTTP connections (keep-alive header automatically added)
      connectTimeout = 600000                          # Timeout when establishing a connection
      handshakeTimeout = 600000                        # Timeout when performing TLS hashshake
      pooledConnectionIdleTimeout = 600000             # Timeout when a connection stays unused in the pool
      readTimeout = 600000                             # Timeout when a used connection stays idle
      #maxRetry = 2                                    # Number of times that a request should be tried again
      requestTimeout = 600000           

Solution

As per comments from Rcordoval -

Check this property: spring.mvc.async.request-timeout= # Amount of time before asynchronous request handling times out

This setting helps with rest of gatling configurations

spring.mvc.async.request-timeout=1200000

The root cause however is that when requests come in large numbers, then all worker threads (200) get occupied in uploading open connections (2000) (the Controller is taking MultipartFile as argument and returning a DeferredResult )

I think DeferredResult shines when request serve logic is fast and business logic is slow (runs on forkjoin.commonPool). It does not quite fits with MultiPartFile uploads (blocking and slow) and more so when File sizes are big since then responses are not quickly resumed (as can be seen in above response per sec chart, only after few seconds responses start resuming since open connections are 2000 and workers only 200). If workers are increased, it then mitigates advantages of async processing anyway.

In this case, request processing (upload and blocking) was slow and business logic was fast. so responses were getting ready but all the worker threads (200) are so busy serving more and more requests that responses are not getting resumed and timing out as a result.

Probably makes a case for having separate pool for request serve and response resume in async processing with DeferredResult ?