Zeppelin Link to Spark Master (in Docker Container)

Question

Thanks for sharing your time.

I have a Docker Set-Up from the following: A Docker-Compose file that launches an instance of Zookeeper, Solrcloud, Spark Master / Worker and Zeppelin. They all start up fine and work. Solrcloud and Spark connect with Zookeeper. Now I wanted to connect Zeppelin to the Spark Master. But this does not work for me.

In my docker build file, I installed ZEPPELIN_SPARK_MASTER: spark://spark:7077and installed SPARK_HOME. However, it does not work, as I see in the Spark user interface (only Spark Worker is displayed). All ports are open. I turned off the firewall and still did not work. - Ubuntu 16.04 LTS