504 in communication between microservices

I am working in a Spring boot project and deploy on 3 nodes docker swarm worker as a replicate, When goes under heavy load after 150 request it's get 504 gateway timeout and didn't response until reload. after reload container everything it we'll be OK.

Rest Template config :

@Bean("restTemplate")
public RestTemplate createRestTemplate(RestTemplateBuilder builder) {
    log.info("RestTemplate..");
    return builder
            .setConnectTimeout(Duration.ofMillis(5000))
            .setReadTimeout(Duration.ofMillis(40000))
            .build();
}

tomcat webservice config in application.yml :

tomcat:
    max-connections: 2000
    connection-timeout: 600s
    threads:
      max: 100000   jetty:
    connection-idle-timeout: 10s

how I can resole this problem ?