Don't worry this is an issue that many Drupal developers have come across. In particular it raises its head when you add a subdomain.  Your Drupal website is only showing a plain white screen with “The provided host name is not valid for this server" on it. What does it mean and how to fix it. Drupal 8 added a security feature show it isn't possible to spoof the HTTP Host header and trick Drupal into using a different domain name.  Smart move.  So this...

Running a common composer command, post an upgrade on the server to Centos 7 and I received the following error: /usr/local/bin/composer: line 8: 6210 KilledThe "Killed" message usually means that your process consumed too much memory, so you may simply need to add more memory to your system if possible.  You can increase the memory, however, note that you shouldn't be doing this action on a production server, and additionally you shouldn't be using composer update at all....