[undertow-dev] Reverse proxy blocked connection after 503

Hi Undertow-dev, we are using the Wildfly(10.1)/Undertow as reverse proxy and facing the following issue: The back end hots behind the reverse proxy are load balanced and ssl terminated by HaProxy. When the real back ends are shutdown the Undertow responds the request immediately with 503 error that sends by the HaProxy. This behavior happens as many times as many connections are set to the reverse proxy. After the max connections/thread are exceeded the responses are stucked and wit for the connection timeout. It seems to me that after the 503 may the HaProxy wants to close the socket but the Undertow keeps it alive but not allow to be accessed by new request. It is released after a while my the operating system free the socket or there are default idle timeout and the undertow renew the stucked connections. Are there any configuration that solves the above issue? Thank you forward, Zsolt