I had originally posted this on Superuser, but for some reason it got marked off-topic, so this seems like the only reasonable place left to post this.
I have a web server, which hosts my website (https://thijs365.com/) and my Nextcloud server (https://cloud.thijs365.com). That Nextcloud server is configured to use a OnlyOffice document server (https://docservice.thijs365.com/). However, the Nextcloud install can't reach the document server. After some digging around, I found that I also wasn't able to
curl -L my website; it just times out. Nginx is configured to proxy-pass to the document server. I have split up my config into multiple files; you can find my config for thijs365.com here, the docservice config can be found here, the ssl config here, the nextcloud config here, and the php config here. My web server runs Ubuntu 18.04, and my document server runs CentOS 7.
I have found that
curling from my laptop does work, which means that the servers can't reach each other internally.