If you want to use Filebeat in dockware, you do not only need to turn ON the feature, but also provide a valid filebeat configuration.
The easiest way to do this, is to mount that single file into /etc/filebeat/filebeat.yml.
In addition to this, your Docker container must have access to your logstash container by either using the links or networks in Docker. This needs to be done only if you also have your Logstash within your Docker network :)
Here is an example of a filebeat.yml configuration: