Apache

Running a redundant apache server does not require much from apache itself, but rather the underlying filesystem and a proxy in front of it. The filesystem is important, so the website can be shared between the servers. For this we will use GlusterFS. PHP sessions will have to be shared between the webservers as well and finally we will put a proxy in front of apache, which will be a combination of Corosync and HA-proxy.

In this setup we will configure 2 apache servers. None of these will be master/slave/primary/secondary. They will just be running with the same configuration. Since the servers are configured the same way it makes sense to share some files.

192.168.1.51 www (virtual IP-address)
192.168.1.52 www01
192.168.1.53 www02

Software

apt-get install apache2 php php-mysql memcached php-memcache php-mcrypt

Filesystem

Configure your system as a GlusterFS client, so you have the following in your fstab.

/etc/glusterfs/www.vol /var/www glusterfs defaults,_netdev,rw 0 0

Testpage

Make a simple webpage, that shows something unique about the system. This is usefull when debugging. index.php

   1 <?php
   2         echo "client: " . $_SERVER['REMOTE_ADDR'] . "\n";
   3         echo "server: " . $_SERVER['SERVER_ADDR'] . "\n";
   4         echo "hostname: " . gethostname() . "\n";
   5 ?>

PHP Sessions

Creating a PHP session on one webserver, does not create it on the other. As requests bounces back and forth between the two webservers, this will be a problem for PHP sites. The solution is called memcached.

Add this to /etc/php/7.0/mods-available/memcache.ini.

memcache.allow_failover="1"
memcache.hash_strategy="consistent"
memcache.hash_function="crc32"
memcache.session_redundancy=3
memcache.maxreclevel=0
memcache.maxfiles=0
memcache.archivememlim=0
memcache.maxfilesize=0
memcache.maxratio=0

In /etc//php/7.0/apache2/php.ini find the entry session.save_handler = files and change it to the following.

session.save_handler = memcache
session.save_path = "tcp://www01:11211, tcp://www02:11211"

References

https://www.globo.tech/learning-center/php-memcached-instances-ubuntu-16/

-  ⇤ ← Revision 1 as of 2017-12-22 22:49:10 → 
  Size: 67
  Editor: Kristian Kallenberg
  Comment:
+   ← Revision 33 as of 2020-02-10 00:49:20 → ⇥
  Size: 2356
  Editor: Kristian Kallenberg
  Comment:
-Deletions are marked like this.
+Additions are marked like this.
 Line 1:
+incomplete, do not use!
-Line 2:
+Line 3:
+Running a redundant apache server does not require much from apache itself, but rather the underlying filesystem and a proxy in front of it. The filesystem is important, so the website can be shared between the servers. For this we will use [[GlusterFS|GlusterFS]]. PHP sessions will have to be shared between the webservers as well and finally we will put a proxy in front of apache, which will be a combination of [[Corosync and HA-proxy|Corosync and HA-proxy]].

In this setup we will configure 2 apache servers. None of these will be master/slave/primary/secondary. They will just be running with the same configuration. Since the servers are configured the same way it makes sense to share some files.

 * 192.168.1.51 www (virtual IP-address)
 * 192.168.1.52 www01
 * 192.168.1.53 www02
-Line 6:
+Line 15:
-apt-get install apache2
+apt-get install apache2 php php-mysql memcached php-memcache php-mcrypt
-Line 8:
+Line 17:
+== Filesystem ==

Configure your system as a [[GlusterFS Client|GlusterFS client]], so you have the following in your fstab.
{{{
/etc/glusterfs/www.vol /var/www glusterfs defaults,_netdev,rw 0 0
}}}

== Testpage ==
Make a simple webpage, that shows something unique about the system. This is usefull when debugging.
`index.php`
{{{#!highlight php
<?php
        echo "client: " . $_SERVER['REMOTE_ADDR'] . "\n";
        echo "server: " . $_SERVER['SERVER_ADDR'] . "\n";
        echo "hostname: " . gethostname() . "\n";
?>
}}}

== PHP Sessions ==

Creating a PHP session on one webserver, does not create it on the other. As requests bounces back and forth between the two webservers, this will be a problem for PHP sites. The solution is called memcached.

Add this to `/etc/php/7.0/mods-available/memcache.ini`.

{{{
memcache.allow_failover="1"
memcache.hash_strategy="consistent"
memcache.hash_function="crc32"
memcache.session_redundancy=3
memcache.maxreclevel=0
memcache.maxfiles=0
memcache.archivememlim=0
memcache.maxfilesize=0
memcache.maxratio=0
}}}

In `/etc//php/7.0/apache2/php.ini` find the entry `session.save_handler = files` and change it to the following.
{{{
session.save_handler = memcache
session.save_path = "tcp://www01:11211, tcp://www02:11211"
}}}


== References ==
 * https://www.globo.tech/learning-center/php-memcached-instances-ubuntu-16/