Ubuntu : Apache2 : AH01144: No protocol handler was valid for the URL / (scheme 'http'). If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.

 If you get the below error,

AH01144: No protocol handler was valid for the URL / (scheme 'http'). If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.

Then enable necessary proxy modules using below commands (Credits)

sudo a2enmod ssl
sudo a2enmod proxy
sudo a2enmod proxy_balancer
sudo a2enmod proxy_http