We have an installation of Nextcloud 21.0.1, with the connector for MS Office Online 2019. The Nextcloud instance is accessible both from the local intranet and on the Internet (using HA Proxy).
Apache2 is used as a webserver, with SSL certificates issued by the RootCA of the local intranet.
And HA Proxy is configured with SSL certificates from Let’s Encrypt, for correct HTTPS access from the outside.
However. When we access Nextcloud using the local intranet URL, https://cloud.intradomain.local/, everything works perfectly: we can open and edit any document from Word, Excel, etc. The problem occurs when we access Nextcloud using the public URL https://cloud.publicdomain.com/ (it does not matter if we are inside or outside the local intranet), when this is the case, no Office document can ever be opened, and we always get an error message like “Unable to Open the file”.
We think that we should touch some configuration in the reverse proxy HA Proxy, but we are not sure what to modify there.
Or maybe change something in the IIS instance … but IIS is a weirdo when you come from the Apache/Unix world.
We have tried changing the DNS resolution (by editing C:\Windows\system32\drivers\etc\hosts file) on the MS Office Online document server, so that the public address is resolved to the local IP of the Nextcloud server, but without success.
Any ideas / help you can give us?
Keep in touch.