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Sticky session load balancing with Apache and mod_balancer on Ubuntu Linux

Posted on April 15, 2011

Apache 2.2 can do load balancing with sticky sessions. However, there is a catch. You need to use mod_headers module to set a cookie based on the chosen balancer member for the first request and then route the subsequent requests to this client.

Use cases

The method described here works in every situation and does not rely on client IP address, etc. The only downside is that if one balancer member goes down all subsequent requests for it will die. So this method can be only used for load balancing, not for high availability (I am not sure if BALANCER_ROUTE_CHANGED environment variable is set when a balancer member is lost and would redirect the clients to a new balancer member).

This requests were tested on Ubuntu Linux, but may as well work in other environments.

Setting route configution in virtual host

Create a balancer

<Proxy balancer://yourlb>
 BalancerMember http://127.0.0.1:13001/ route=1
 BalancerMember http://127.0.0.1:13002/ route=2
 BalancerMember http://127.0.0.1:13003/ route=3
 BalancerMember http://127.0.0.1:13004/ route=4
</Proxy>

Set the cookie using mod_headers. Note that the cookie must be in format [session name].[route id] (the dot is required). It seems to be possible to leave session name empty.

Header add Set-Cookie "ROUTEID=.%{BALANCER_WORKER_ROUTE}e; path=/" env=BALANCER_ROUTE_CHANGED

Make ProxyPass  follow the cookie (Zope virtual host monster style with HTTPS)

ProxyPass / balancer://lbsits/http://localhost/VirtualHostBase/https/yoursite.org:443/yourplonesiteid/VirtualHostRoot/ stickysession=ROUTEID

Note: Hard restart is required. apache2ctl graceful is not enough to make new balancer rules effective.

Testing

Use wget

wget -S https://yoursite.org/

See that Set-Cookie: ROUTE_ID is present and it contains a valid value (is not empty)

HTTP/1.1 200 OK
 Date: Wed, 13 Apr 2011 15:21:52 GMT
 Server: Zope/(Zope 2.10.9-final, python 2.4.5, linux2) ZServer/1.1 Plone/3.3.3
 Content-Length: 23197
 Expires: Sat, 01 Jan 2000 00:00:00 GMT
 Content-Type: text/html;charset=utf-8
 Content-Language: en
 Set-Cookie: I18N_LANGUAGE="en"; Path=/
 Set-Cookie: ROUTEID=.1; path=/

More info

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Copy/move phpBB3 forum from a server to another computer (Ubuntu/Linux)

Posted on March 30, 2011

Here are short instructions what you need to do in order to move / copy phpBB3 forum.

Prerequisites

What you need in order to benefit from these instructions

  • Basic UNIX command-line knowledge
  • SSH access to the server
  • MySQL access to the database
  • LAMP stack ready on the new server

These instructions have been tested on Ubuntu/Debian/Linux but they should work in other environments too.

Write down database access information

Get password from config.php file on the old server:

cd /var/www/phpBB3
cat config.php

Write down database name, username and password.

Copy files

Use rsync to remotely copy forum files to a new computer. On new computer, in /var/www folder

rsync -av --compress-level=9 user@oldserver.com:/var/www/phpBB3 .

Dump and copy database

Execute the following command on the new server. It takes SSH connection to the old server and dumps phpBB3 database to the new server over the SSH connection.

ssh user@oldserver.com -C -o CompressionLevel=9 mysqldump -u databaseuser --password=databasepassword --skip-lock-tables --add-drop-table databasename > phpbb3.sql

Create a new database

Use the old access information from config.php to create a database with identical access information on the new server. You need a MySQL root access to create new databases.

mysql -uroot -p

Create database and grant access to phpBB3 user for it.

mysql> create database databasename;
mysql> GRANT ALL ON databasename.* TO 'databaseuser'@'localhost' identified by 'databasepassword';

Load the database on the new server from the dump file:

mysql> connect databasename;
mysql> source phpbb3.sql

Configure Apache virtualhost for the new server

The last step is to set-up Apache virtual host on the new server, so you can access the phpBB3 using a domain name. Note that this doesn’t need to be a real domain name, but you can spoof the domain name using /etc/hosts file on your local workstation.

Add file /etc/apache2/sites-enabled/phpbb3.conf (or pick a filename based on forum name if you host multiple forums)

<VirtualHost *>
 ServerName yourdomainname.com

 DocumentRoot /var/www/phpBB3
 <Directory />
   Options FollowSymLinks
   AllowOverride None
 </Directory>

</VirtualHost>

Note that <virtualhost *> may change depending on how Apache has been set up to listen IP addresses and ports. Also if you are using a shared hosting package or VPS you might need to use the server control panel (cPanel) to do this step.

Then check if your new config file is ok and restart Apache:

apache2ctl configtest
apache2ctl graceful

Hosts spoofing trick

If you are not having a DNS server of your own which you can use for the copy you can always use /etc/hosts file trick to spoof domain names. This way you can make Apache to serve the forum from the server even if the forum is not connected to any real domain name yet.

 

 

 

 

 

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Enable PHP log output (error_log) on XAMPP on OSX

Posted on March 16, 2011

If you are using XAMPP to develop PHP software (WordPress, Joomla!) on OSX you might want to get some advanced logging output from your code. PHP provides nice error_log() function, but it is silent by default. Here are short instructions how to enable it and follow the log.

Use your favorite editor to edit php.ini file in /Applications/XAMPP/etc/php.ini – sudo priviledges needed, Smultron does it out of the box.

Change lines:

log_errors = Off
;error_log = filename

To:

log_errors = on
error_log = /tmp/php.log

Restart Apache using XAMPP controller in Finder -> Applications.

Now use the following UNIX command to see continuous log flow in your terminal:

tail -f /tmp/php.log

See also the earlier article about XAMPP and file permissions.

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Setting up Apache virtual hosts behind Varnish

Posted on March 4, 2011

Varnish is a very fast front end cache server. You might want to use it at the front of Apache to speed up loading of your static pages and static media, for example for your WordPress blog. You can also use Varnish backends to multiplex the requests between Plone and Apache based PHP software running on the same server using different backend directives.

However if you wish to use Apache virtual hosts with Varnish there is a trick in it.

We use the following setup

  • Varnish listens to port 80, HTTP
  • Apache listens to port 81
  • Varnish uses Apache as a backend

The related varnish.vcl is

backend backend_apache {
.host = "127.0.0.1";
.port = "81";
}

sub vcl_recv {
 ...
 elsif (req.http.host ~ "^blog.mfabrik.com(:[0-9]+)?$") {
    set req.backend = backend_apache;
 }
 ...
}

Note that the backend IP is 127.0.0.1 (localhost). By default, with Debian or Ubuntu Linux, Apache configuration does not do virtual hosting for this.

So if /etc/apache2/sites-enabled/blog.mfabrik.com looks like:

<VirtualHost *:81>

 ServerName blog.mfabrik.com
 ...
 LogFormat       combined
 TransferLog     /var/log/apache2/blog.mfabrik.com.log

 ...

 ExpiresActive On
 ExpiresByType image/gif A3600
 ExpiresByType image/png A3600
 ExpiresByType image/image/vnd.microsoft.icon A3600
 ExpiresByType image/jpeg A3600
 ExpiresByType text/css A3600
 ExpiresByType text/javascript A3600
 ExpiresByType application/x-javascript A3600
</VirtualHost>

And now the trick – you need to add the following to /etc/apache2/httpd.conf

NameVirtualHost *:81

Unless you do all this, Apache will just pick the first virtualhost file in /etc/apache2/sites-enabled and use it for all requests.

Also you need to edit ports.conf and change Apache to listen to port 81:

Listen 81

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