Joining the many other www pages about opening up your host firewall to allow nfs is this one!
On CentOS 7, which went systemd for better or for worse, firewalld is the default firewall solution. I like how everything is a file, so you can just use xml to make things extensible.
firewall-cmd --permanent --add-service=nfs --add-service=rpc-bind --add-service=mountd
That’s it! You just need to open up the predefined services nfs, rpc-bind, and mountd. Thanks to all the countless posts out there that helped me research this. I didn’t save any of the links, because this time I’m assuming it’s such general knowledge it doesn’t need special credits.
Bonus: if you want to read the definitions of the predefined services and other elements for firewalld, check out directory /usr/lib/firewalld/. I know I’ve written my own service definitions (for Plex Media Server) in the past.