Hello Siwat2545 and thank you for your time.
I can't ping office.mydomain.com from nextcloud container.
But i can with my computer.
I can ping the app IP (172.19.x.x) with nextcloud container.
I think that it may be a problem with my pfsense box, because when i try to ping office.mydomain.com with nextcloud container, it receive the right adress (my public IP) but doesn't get any response.
Only office, nextcloud and letsencrypt are all three on the same docker network created for them.
Thanks !
EDIT :
I fixed my problem with wireshark and long investigate.
I've seen that when nextcloud try to communicate with OnlyOffice through https://office.mydomain.com, when the packet arrive at my pfsense router/firewall box, it is like this :
FROM 10.10.X.X (IP Unraid) TO 127.0.0.1:19001
And i'm a 'block all' type of guy, so i've set pfsense to allow pack from unraid to web only on HTTP and HTTPS port.
So i added a rule to let Unraid IP send packet to 127.0.0.1:19001
But i'm a little confuse about that.
It works, and i see packets from unraid to 127.0.0.1:19001 pass through when i test OnlyOffice from Nextcloud, but if i'm not to bad, 127.0.0.1 is localhost, so it doesn't have to go to the pfsense box...
But the problem is fixed so it's ok If someone can understand this, its a big plus ^^
Hope that will fixes some people's problems
(Sorry for my poor English)