MariaDB Galera Cluster - first node won't reconnect after restart... Ever
With not so much detail in the question, I can't give a detailed answer, but I'd recommend starting with MariaDB's documentation about Galera Cluster since you're using MariaDB. See e.g. Getting Started with MariaDB Galera Cluster. The DigitalOcean documentation you referred to is for MySQL 5.6, so there may be details in there that works slightly differently on MariaDB.

Maybe the most crucial question about your specific problem is: What error message are you getting? And I mean the actual error message in the MariaDB error log, which is not necessarily what systemctl will show you in the shell when you run the start/restart/status commands. Once you have this, try your favourite search engine to find the answer. If that doesn't work, come back to DBA.SE and ask a more specific question which includes the error message(s). 

Galera Cluster is an excellent technology, but if you don't have much experience with it yet, make sure to read carefully about its limitations, and make sure they're not in conflict with your particular use-case. There is a lot to learn, so be prepared to invest sufficient time and effort.