Error 503 when trying to access Collabora Online on my Raspberry Pi 4

I am running nextcloud on my Raspberry Pi 4 4GB which works fine! (internal IP of RPi:
Now I would also like to run Collabora Online on my Pi4. But because Libre Office Online seems not to support ARM architectures I tried to use docker.

I did the following steps:

  • nextcloud is running at the subdomain “
  •” is installed and working with https
  • a2enmod proxy, a2enmod proxy_wstunnel, a2enmod proxy_http and a2enmod ssl enabled
  • collabora docker image pulled “via docker pull collabora/code”
  • image installed with command “docker run -t -d -p -e ‘domain=cloud\.fcar\.tech’ -e ‘dictionaries=de en’ -e “username=admin” -e “password=[PASSWORD]” --restart always --cap-add MKNOD collabora/code”

I have the following apache config file for the docs subdomain:
<VirtualHost default:443>

	DocumentRoot /var/www/html/docs/
	<IfModule mod_headers.c\>
		Header always set Strict-Transport-Security "max-age=15768000; includeSubDomains; preload"
	SSLEngine on
	Include    /etc/letsencrypt/options-ssl-apache.conf
	ErrorLog ${APACHE_LOG_DIR}/error.log
	CustomLog ${APACHE_LOG_DIR}/access.log combined
	SSLProtocol all -SSLv2 -SSLv3
	SSLHonorCipherOrder on

	# Encoded slashes need to be allowed
	AllowEncodedSlashes NoDecode

	# Container uses a unique non-signed certificate
	# Container uses a unique non-signed certificate
	SSLProxyEngine On
	SSLProxyVerify None
	SSLProxyCheckPeerCN Off
	SSLProxyCheckPeerName Off

	# keep the host
	ProxyPreserveHost On

	# static html, js, images, etc. served from loolwsd
	# loleaflet is the client part of LibreOffice Online
	ProxyPass /loleaflet retry=0
	ProxyPassReverse /loleaflet

	# WOPI discovery URL
	ProxyPass	   /hosting/discovery retry=0
	ProxyPassReverse    /hosting/discovery

	# Main websocket
	ProxyPassMatch	   "/lool/(.*)/ws$" wss://$1/ws nocanon

	# Admin Console websocket
	ProxyPass    /lool/adminws wss://

	# Download as, Fullscreen presentation and Image upload operations
	ProxyPass /lool
	ProxyPassReverse   /lool

	# Endpoint with information about availability of various features
	ProxyPass	   /hosting/capabilities retry=0
	ProxyPassReverse    /hosting/capabilities
	SSLCertificateFile	   /etc/letsencrypt/live/
	SSLCertificateKeyFile    /etc/letsencrypt/live/


When opening “” I get “Error 503 - Service unavailable”.
The apache2 log says at that point:

[Fri Oct 25 15:01:07.652319 2019] [proxy:error] [pid 22213] (111)Connection refused: AH00957: HTTPS: attempt to connect to ( failed
[Fri Oct 25 15:01:07.652498 2019] [proxy_http:error] [pid 22213] [client] AH01114: HTTP: failed to make connection to backend:

What can cause this problem?
Is collabora even working on a Raspberry Pi 4 with docker?
Did I do something wrong while setting up?
Is there a problem with my proxy or IP settings?

Thank you for your Help in advance!

I had the same problem and then I found out that there is no docker image for the Raspberry Pi: