I installed collabora on a debian stretch instance without docker.
After some struggles I got it to work.
did the trick.
Still fonts used on the users laptops and desktops (microsoft) using LibreOffice and some MSOffice are not available.
A possibile solution in https://help.nextcloud.com/t/i-want-to-prevent-design-collapse-by-font-in-collabora/22676/7 did not work.
(Same I found in https://central.owncloud.org/t/howto-install-collabora-online-on-ubuntu-16-04-without-docker/3844/9)
The way to add fonts that did work I found here: https://www.pcworld.com/article/2863497/how-to-install-microsoft-fonts-in-linux-office-suites.html.
It is explained for Ubuntu, but also works in debian.
For the core MS fonts:
sudo apt-get install ttf-mscorefonts-installer
You may be asked to accept the license agreement, i was not asked.
They end up in /usr/share/fonts/truetype/msttcorefonts
Next is to install the clear types such as calibri.
This is a bit different but can be done with the vista fonts installer script.
Make sure you have the appropriate permissions.
Create a .font folder as the script needs that.
wget -qO- http://plasmasturm.org/code/vistafonts-installer/vistafonts-installer | bash
all new fonts are installed in the .font folder
in /usr/share/fonts/truetype create folder msttvistafonts
copy all fonts from the .fonts folder to /usr/share/fonts/truetype/msttvistafonts
change the ownerships to the same as that in the other fonts if needed.
Restart loolwsd.service and the fonts are available.