A little tuto can help under ispconfig 3.1 to enable the http/2 protocols
Http/2 protocols increase the speed to display your website.
you can test there : https://tools.keycdn.com/http2-test
or via this command :
1 - edit all your website
cd /etc/apache2/sites-available
to test
sudo a2enmod http2
and restart apache2
Number 1 : Install all the website
cd /etc/apache2/sites-available
nano mydomain.com
under ServerAdmin add
Protocols h2 http/1.1
restart apache2
/etc/init.d/apache2 restart
make the same thing for all website 2- all new website
vi 000-default.conf
below DocumentRoot add
Protocols h2 http/1.1
3 - Via the panel
edit your website, go to options and apache directive add
Protocols h2 http/1.1