Invalid command 'SSLEngine' Centos
Solution 1:
There is probably some forgotten configuration in /etc/httpd/conf or /etc/httpd/conf.d. Find (grep SSL /etc/httpd/{conf,conf.d} -r) and destroy it or install ssl module for Apache:
yum install mod_ssl
Solution 2:
In my case I had mod_ssl installed but it was not enabled. To do this I ran:
sudo a2enmod ssl
Solution 3:
Check whether you have already loaded mod_ssl in the httpd.conf file:
LoadModule ssl_module modules/mod_ssl.so