Increate max no of open files limit in Ubuntu 16.04 for Apache2

gistfile1.txt

# maximum capability of system
user@ubuntu:~$ cat /proc/sys/fs/file-max
708444

# available limit
user@ubuntu:~$ ulimit -n
1024

# To increase the available limit to say 200000
user@ubuntu:~$ sudo vim /etc/sysctl.conf

# add the following line to it
fs.file-max = 200000

# run this to refresh with new config
user@ubuntu:~$ sudo sysctl -p

# edit the following file
user@ubuntu:~$ sudo vim /etc/security/limits.conf

# add following lines to it
* soft     nproc          200000    
* hard     nproc          200000   
* soft     nofile         200000   
* hard     nofile         200000
root soft     nproc          200000    
root hard     nproc          200000   
root soft     nofile         200000   
root hard     nofile         200000

# edit the following file
user@ubuntu:~$ sudo vim /etc/pam.d/common-session

# add this line to it
session required pam_limits.so

# logout and login and try the following command
user@ubuntu:~$ ulimit -n
200000

# default mod_php just run with mpm_prefork and to get 
# a good and fast setup for Apache mpm_worker is better (much more)
# but to use mpm_work module is necessary to migrate from mod_php to php-fpm

# remove mod_php
user@ubuntu:~$ apt-get remove libapache2-mod-php7.0 

# install php-fpm
user@ubuntu:~$ apt-get -y install php7.0-fpm libapache2-mod-fastcgi

# disable the conflicting modules
user@ubuntu:~$ a2dismod mpm_worker mpm_prefork 

# enable the required modules
user@ubuntu:~$ a2enmod actions fastcgi alias rewrite mpm_event 

# add the following configuration to /etc/apache2/conf-available/php7.0-fpm.conf

<IfModule mod_fastcgi.c>
    SetHandler php7-fcgi .php
    Action php7-fcgi /php7-fcgi virtual
    Alias /php7-fcgi /usr/lib/cgi-bin/php7-fcgi
    FastCgiExternalServer /usr/lib/cgi-bin/php7-fcgi -socket /var/run/php/php7.0-fpm.sock -pass-header Authorization -idle-timeout 3600
    <Directory /usr/lib/cgi-bin>
        Require all granted
    </Directory>
</IfModule>

# enable the php-fpm configuration
sudo a2enconf php7.0-fpm 

# restart services
service apache2 restart
service php7.0-fpm restart

# in Apache2 main config /etc/apache2/apache2.conf
<IfModule mpm_worker_module>
    ServerLimit              250
    StartServers              10
    MinSpareThreads           75
    MaxSpareThreads          250 
    ThreadLimit               64
    ThreadsPerChild           32
    MaxRequestWorkers       8000
    MaxConnectionsPerChild 10000
</IfModule>