After some times, greenwall crashes for too many open files

[lfoppiano]

Dear all,
after a while greenwall is having some issues with the number of open files:

Aug 06 13:09:39 falcon greenwall[5769]: 2019/08/06 13:09:39 http: Accept error: accept tcp [::]:9001: accept4: too many open files; retrying in 1s
Aug 06 13:09:39 falcon greenwall[5769]: 2019/08/06 13:09:39 Get http://localhost/webanno/login.html: dial tcp: lookup localhost: device or resource busy
Aug 06 13:09:40 falcon greenwall[5769]: 2019/08/06 13:09:40 http: Accept error: accept tcp [::]:9001: accept4: too many open files; retrying in 1s
Aug 06 13:09:41 falcon greenwall[5769]: 2019/08/06 13:09:41 http: Accept error: accept tcp [::]:9001: accept4: too many open files; retrying in 1s
Aug 06 13:09:42 falcon greenwall[5769]: 2019/08/06 13:09:42 http: Accept error: accept tcp [::]:9001: accept4: too many open files; retrying in 1s
Aug 06 13:09:43 falcon greenwall[5769]: 2019/08/06 13:09:43 http: Accept error: accept tcp [::]:9001: accept4: too many open files; retrying in 1s
Aug 06 13:09:44 falcon greenwall[5769]: 2019/08/06 13:09:44 http: Accept error: accept tcp [::]:9001: accept4: too many open files; retrying in 1s
Aug 06 13:09:45 falcon greenwall[5769]: 2019/08/06 13:09:45 http: Accept error: accept tcp [::]:9001: accept4: too many open files; retrying in 1s
Aug 06 13:09:46 falcon greenwall[5769]: 2019/08/06 13:09:46 http: Accept error: accept tcp [::]:9001: accept4: too many open files; retrying in 1s
Aug 06 13:09:47 falcon greenwall[5769]: 2019/08/06 13:09:47 http: Accept error: accept tcp [::]:9001: accept4: too many open files; retrying in 1s
Aug 06 13:09:48 falcon greenwall[5769]: 2019/08/06 13:09:48 http: Accept error: accept tcp [::]:9001: accept4: too many open files; retrying in 1s
Aug 06 13:09:49 falcon greenwall[5769]: 2019/08/06 13:09:49 http: Accept error: accept tcp [::]:9001: accept4: too many open files; retrying in 1s
Aug 06 13:09:50 falcon greenwall[5769]: 2019/08/06 13:09:50 http: Accept error: accept tcp [::]:9001: accept4: too many open files; retrying in 1s
Aug 06 13:09:51 falcon greenwall[5769]: 2019/08/06 13:09:51 http: Accept error: accept tcp [::]:9001: accept4: too many open files; retrying in 1s

If I restart the service everything goes back to normal...

I've checked the open files and it seems that the connections are not closed correctly, perhaps something wrong in my configuration?

Redirecting to /bin/systemctl start greenwall.service
(base) [Luca@falcon ~]$ lsof | grep greenwall | wc -l 
77
(base) [Luca@falcon ~]$ lsof | grep greenwall | wc -l 
306
(base) [Luca@falcon ~]$ lsof | grep greenwall | wc -l 
920

and here a more detailed view:

greenwall 31633          Luca   44u     IPv6              67288          0t0        TCP localhost:56530->localhost:http (CLOSE_WAIT)
greenwall 31633          Luca   45u     IPv6             303313          0t0        TCP localhost:56534->localhost:http (CLOSE_WAIT)
greenwall 31633          Luca   46u     IPv6              67295          0t0        TCP localhost:56564->localhost:http (CLOSE_WAIT)
greenwall 31633          Luca   47u     IPv6              72439          0t0        TCP localhost:56518->localhost:http (CLOSE_WAIT)
greenwall 31633          Luca   48u     IPv6              72454          0t0        TCP localhost:56546->localhost:http (CLOSE_WAIT)
greenwall 31633          Luca   49u     IPv6             304148          0t0        TCP localhost:56566->localhost:http (CLOSE_WAIT)
greenwall 31633          Luca   50u     IPv6             303831          0t0        TCP localhost:56568->localhost:http (CLOSE_WAIT)
greenwall 31633          Luca   51u     IPv6              77354          0t0        TCP localhost:56567->localhost:http (CLOSE_WAIT)
greenwall 31633          Luca   52u     IPv6              70510          0t0        TCP localhost:56578->localhost:http (CLOSE_WAIT)
(base) [Luca@falcon ~]$ 

I'm running it with Centos 7.