Unable to register instance with rocket chat cloud

Hi!

I’m using rocketchat on a UCS system (docker based) for quite a while and after several updates I’m now on version 3.18.2 . After 2 years of usage I would like to register my instance in the rocket chat cloud to get the benefit of push notifications, but the “connectivity services” tab is making me a hard time.
I created a new account in the rocket chat cloud and created a token (workspaces → register self-managed). In the connectivity services tab after pasting the token from the clipboard and pressing “connect”, the only thing I get is a small popup telling me An error occured connecting.

For my users, the rocket chat is working fine. So network connectivity seems to be ok. The system has also internet access via NAT performed by the docker host.

I haven’t found any hint in the logs or somewhere else what the problem might be.
Any idea on how to debug this?

Thx a lot for any help!

Server Setup Information

  • Version of Rocket.Chat Server: 3.18.2 (seems to be the latest version provided by the Univention App Center)
  • Operating System: Univention Corporate Server 4.4-8 / docker container
  • Deployment Method: docker (from Univention App Center)
  • Number of Running Instances: 1
  • NodeJS Version: 12.22.1
  • MongoDB Version: 4.0.19 / mmapv1 (oplog Enabled)
  • Proxy: apache
  • Firewalls involved: only NAT, no packetfilter/proxy

Looks like the docker container that is provided by the Univention App Center uses the IP address 127.0.0.11 as nameserver. But there seems to be no nameserver running at that address → all cloud services of rocketchat are unavailable.

After fixing that, the registration worked as expected:

host# docker exec -ti -u 0 rocketchat_rocketchat_1 /bin/bash
container# echo "nameserver 8.8.8.8" > /etc/resolv.conf
container# echo "options timeout:2 ndots:0" >> /etc/resolv.conf
container# exit
host#
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