➥ Enable apache2 cache to speed up your website on ubuntu 17.04

First enable the mods:
sudo a2enmod file_cache
sudo a2enmod headers
sudo a2enmod expires

Then restart the apache service:
service apache2 restart

Then edit the virtual host:
pico /etc/apache2/sites-enabled/000-default.conf

And add ifmodule between virtual host:
<VirtualHost *:80>
ServerName www.webleit.info
ServerAdmin admin@webleit.info
DocumentRoot /var/www/html

# Available loglevels: trace8, ..., trace1, debug, info, notice, warn,
# error, crit, alert, emerg.
# It is also possible to configure the loglevel for particular
# modules, e.g.
#LogLevel info ssl:warn
ErrorLog ${APACHE_LOG_DIR}/error.log
CustomLog ${APACHE_LOG_DIR}/access.log combined
#Include conf-available/serve-cgi-bin.conf
<IfModule mod_expires.c>
# Turn on the module.
ExpiresActive on
# Set the default expiry times.
ExpiresDefault "access plus 2 days"
ExpiresByType image/jpg "access plus 1 month"
ExpiresByType image/gif "access plus 1 month"
ExpiresByType image/jpeg "access plus 1 month"
ExpiresByType image/png "access plus 1 month"
ExpiresByType text/css "access plus 1 month"
ExpiresByType text/javascript "access plus 1 month"
ExpiresByType application/javascript "access plus 1 month"
ExpiresByType text/x-javascript "access plus 1 month"
ExpiresByType application/x-shockwave-flash "access plus 1 month"
ExpiresByType text/css "now plus 1 month"
ExpiresByType image/ico "access plus 1 month"
ExpiresByType image/x-icon "access plus 1 month"
ExpiresByType text/html "access plus 600 seconds"
</IfModule>
</VirtualHost>

# vim: syntax=apache ts=4 sw=4 sts=4 sr noet

Then restart again the apache service:
service apache2 restart