What does one do when a large, clustered environment, say 15 or more front-end application servers, starts to choke up an NFS server, or your nodes are reading stale data due to the NFS protocol limitations? What should you do when gigabit Ethernet no longer provides sufficient throughput on your back end storage infrastructure to deliver your files to the world wide web? You implement GFS2.

If you want to know more about the difference between these two filesystems, you can read the comparison here.

I recently set up a small test environment to muck around with GFS, and the result turned out fairly decent and didn’t take a whole lot of time, either.

I’m assuming that if you are reading my blog, technology interests you, and you have heard of GFS2 or the Red Hat Clustering Suite before. But what is it? How does it work? I’ll try to explain a bit about it here.

GFS2 operates on block devices, not virtual “export” directories or “shares”, like CIFS or NFS do. So how is that going to help us achieve a shared file system among all of our web servers if it operates on block devices? There are many answers to that question, only one of which I have explored so far. You can attach block storage to remote systems in a number of different ways, to name a few:

1. iSCSI – Probably the easiest, certainly the least expensive.
2. ATAoE – Similar to the above, however, ATA-over-Ethernet is exactly that, where iSCSI is Internet SCSI over TCP/IP.
3. Fibre Channel – Probably the best-performing option, and probably the most expensive

At work, I will most likely be using Ethernet exclusively, so I naturally chose iSCSI as my transport. iSCSI will enable me to export a block device on my shared storage for use on multiple remote systems. Let’s explore how that is done, as without shared block storage, GFS2 isn’t going to do much for us.

Defining an iSCSI target
Firstly, we need to designate our iSCSI target, or in other words, the storage target that the application servers will be accessing. In this example I will be using just one iSCSI target, which I intend to later have serving my “vhosts” directory for web data. Let’s call our iSCSI target system ‘storage1′. It is going to need software for creating iSCSI targets, so let’s go ahead and install the package “scsi-target-utils”:

# /usr/bin/yum -y install scsi-target-utils

This package contains some useful commands that we will use to create the iSCSI target. namely, “tgtadm”. Before we can use any of them though, we need to start up the targeting service:

# service tgtd start
Starting SCSI target daemon:                               [  OK  ]

Now let’s attempt to create a new target. For simplicity’s sake, I will be naming this particular target “vhosts”. In other examples that I have read through, a rather long string was used as the target name. Using a short name like I am here may have its downside, but other than being easily identifiable I am not sure at this point what the significance is. Fire away:
(more…)

Recently at work, I found myself needing to give a customer access to a few basic statistics on his web servers, but seeing as they are 100% managed, and they get no type of access other than FTP, I had to find a way to deliver them the numbers they wanted by means other than SSH.

FTP would not be a good candidate, it doesn’t make sense that they would need to FTP down a file with stats information every time they wanted to check it out. I decided to “KISS” (keep it simple / stupid) and wrote the following PHP script to get the job done:

<?php
/* Codero Dedicated Support Team <dedicatedsupport@codero.com>
 *
 * File Name: get_server_stats.php
 * Author:    Ryan R. Uber <ryanu@codero.com>
 *
 * Provides an easy http-accessible script to display commonly needed
 * server statics information.
 *
 * Note: Enable exec() to get Apache connection stats.
 * Run:  echo -n "PASSWORD HERE" | md5sum
 *       to generate a password
 */

# Authentication Definitions
$useAuth = false;
$authMD5 = 'Paste generated MD5SUM here';

# Perform login
if ( $useAuth === true )
{
    session_start();

    if ( $_SERVER['REQUEST_METHOD'] == "POST" )
    {
        if ( md5 ( $_POST['password'] ) == $authMD5 )
        {
            $_SESSION['loggedIn'] = 'true';
        }
    }

    # Prompt for password
    if ( ! isset ( $_SESSION['loggedIn'] ) )
    {
?>
<form action=<?=$_SERVER['PHP_SELF']?> method=POST>
<font size=5>Authentication required</font><br>
<font size=2><b><i>Password: </b></i><input type=password name=password><br>
<input type=submit value="Authenticate">
</form>
<?php
        die();
    }
}

# Initialize Variables
$hostname           = $_SERVER['HTTP_HOST'];
$unique             = array();
$www_unique_count   = 0;
$www_total_count    = 0;
$proc_count         = 0;
$display_www        = false;

# Check if 'exec()' is enabled
if ( function_exists ( 'exec' ) )
{
    $display_www = true;

    # Get HTTP connections
    @exec ( 'netstat -an | egrep \':80|:443\' | awk \'{print $5}\' | grep -v \':::\*\' |  grep -v \'0.0.0.0\'', $results );
    foreach ( $results as $result )
    {
        $array = explode ( ':', $result );
        $www_total_count ++;

        if ( preg_match ( '/^::/', $result ) )
        {
            $ipaddr = $array[3];
        }

        else
        {
            $ipaddr = $array[0];
        }

        if ( ! in_array ( $ipaddr, $unique ) )
        {
            $unique[] = $ipaddr;
            $www_unique_count ++;
        }
    }
    unset ( $results );
}

# Get Server Load
$loadavg = explode ( ' ', file_get_contents ( '/proc/loadavg' ) );
$loadavg = "{$loadavg[0]} {$loadavg[1]} {$loadavg[2]}";

# Get Disk Utilization
$disktotal = disk_total_space ( '/' );
$diskfree  = disk_free_space  ( '/' );
$diskuse   = round ( 100 - ( ( $diskfree / $disktotal ) * 100 ) ) . "%";

# Get server uptime
$uptime = floor ( preg_replace ( '/\.[0-9]+/', '', file_get_contents ( '/proc/uptime' ) ) / 86400 );

# Get kernel version
$kernel = explode ( ' ', file_get_contents ( '/proc/version' ) );
$kernel = $kernel[2];

# Get number of processes
$dh = opendir ( '/proc' );
while ( $dir = readdir ( $dh ) )
{
    if ( is_dir ( '/proc/' . $dir ) )
    {
        if ( preg_match ( '/^[0-9]+$/', $dir ) )
        {
            $proc_count ++;
        }
    }
}

# Get memory usage
foreach ( file ( '/proc/meminfo' ) as $result )
{
    $array = explode ( ':', str_replace ( ' ', '', $result ) );
    $value = preg_replace ( '/kb/i', '', $array[1] );
    if ( preg_match ( '/^MemTotal/', $result ) )
    {
        $totalmem = $value;
    }

    elseif ( preg_match ( '/^MemFree/', $result ) )
    {
        $freemem = $value;
    }

    elseif ( preg_match ( '/^Buffers/', $result ) )
    {
        $buffers = $value;
    }

    elseif ( preg_match ( '/^Cached/', $result ) )
    {
        $cached = $value;
    }

}
$freemem = ( $freemem + $buffers + $cached );
$usedmem = round ( 100 - ( ( $freemem / $totalmem ) * 100 )  ) . "%";
?>

<html>
<body>
<font size=5><b><?=$hostname?></b></font><br><br>
<?php
if ( $display_www === true )
{
?>
<font size=4><b>Web Server (80 and 443)</b></font><br>
<font size=3><b><i><?=$www_unique_count?></b></i></font><font size=2> unique connections</font><br>
<font size=3><b><i><?=$www_total_count?></b></i></font><font size=2> total connections</font><br>
<?php
}
?>
<font size=3><i><b>Kernel Version:</b> <?=$kernel?></i></font><br>
<font size=3><i><b>Uptime:</b> <?=$uptime?> days</i></font><br>
<font size=3><i><b>Load Average:</b> <?=$loadavg?></i></font><br>
<font size=3><i><b>Disk Use:</b> <?=$diskuse?></i></font><br>
<font size=3><i><b>Memory Utilization: </b><?=$usedmem?></i></font><br>
<font size=3><i><b>Total Processes: </b><?=$proc_count?></i></font><br>
</body>
</html>

How do I use it?
Just place the above script anywhere in an Apache-servable directory with libphp5 loaded. I attempted to make as much of the script “exec-free” as possible, so currently you only need to configure the exec() function (as mentioned in the script header) if you want to be able to see the number of connections to the Apache webserver. I’m assuming that you have this turned off on your web server, although the PHP default .ini leaves it enabled.

Authentication
This script has a small built in “wanna-be” authentication mechanism. If you want to require a password for a viewer to see this valuable information, all you would need to do is set the “useAuth” variable to “true”, and paste in an md5-hash for the password. I didn’t both with a user for this script.

Get the MD5 password:

$ echo -n 'soooooooSecure' | md5sum

Configure the script:

$useAuth = true;
$authMD5 = "[paste the md5 from the above command here]";

Alternate password method
You can also use a .htaccess file or similar if you want to have multiple users and passwords. Simply disable authentication in the script, and continue on your way with the htpasswd command.

$useAuth = false;