Download and import the official Docker Template.

Make sure, zabbix_agent2 is installed on the server. Add the zabbix user to the docker group and restart the service.

usermod -aG docker zabbix
systemctl restart zabbix-agent2.service                                     

root@dockerhost:~# sudo -u zabbix zabbix_agent2 -t docker.info                      
docker.info                                   [m|ZBX_NOTSUPPORTED] [Cannot fetch data: Get "http://1.28/info": dial unix /run/containerd/containerd.sock: connect: permission denied.]

The zabbix user isn't allowed to access /run/containerd/containerd.sock. This can happen, if the user zabbix is not part of the group docker. To fix it:

usermod -aG docker zabbix