if ($_GET['debug'] == 1) {
define("WP_DEBUG", 1);
}
else {
define("WP_DEBUG", 0);
}


The beauty of the code is that you can trigger debugging easily by adding ?debug=1 onto your uri. This saves you from having to change the wp-config.php file, as well as solves the issue of multiple users/developers.

Note this should only be done on a development site. Having this on a live WordPress install could open up your site to be more easily exploiting as you are giving your attackers access to the notifications, warnings and errors.

One of my big issues with upgrading my hard drive was I wanted to retain all my files, and well pretty much wanted everything to work as it did before (I have multiple partitions, running primarily Ubuntu but also Windows). After a little searching, the best solution appeared to use the dd command.

The beauty of dd is it copies data at the block level, thus you can do exact mirror of drives. While this does take a little extra time it does make for a perfect copy of your current drive. dd is simple to run, but make sure you use the flags correctly. If you reverse the input and output file you can easily destroy your existing drive. Here is the basic command:

dd if=inputfile of=outputfile

Well that is simple enough. To do my hard drive upgrade I simply booted off an Ubuntu cd, opened a terminal, plugged in my new hard drive via a USB case, then ran dd. The process took around 5 hours. When it was done I swapped out my old hard drive for the new one and my system booted flawlessly.

After checking the system booted fine, I booted the Ubuntu cd one more time, then ran gparted and resized my old partitions to take advantage of the extra space of the new drive.

dd is a really simple way to mirror drives or partitions, whether for backing up or migrating to new drives. Just make sure you are absolutely sure about your input and output files to the command, because if you get the wrong, you will find yourself in tears trying to recover your data.

I decided to release the file to the public in case anyone is looking for WordPress syntax highlighting. Note, by no means is this file complete, but is a good base. Feel free to contact me to fill in any functions I am missing.

Download: wordpress.vim (right click, save as)

To install, download and place in your .vim/syntax/ directory. Then load by running in vim:

:set syn=wordpress

Or place something like the following in your .vimrc file:

autocmd BufEnter *.php :set syn=wordpress

Hardware

• Mini Compaq computer with Ubuntu Server installed
• Canon A310 digital camera
• USB Cable
• Dedicated Server Hosted Remotely

Overview

The mini Compaq computer is located at my parents place sitting in their sun room. It is connected to the Internet, as well via a USB cable it is connected to the Canon A310 camera, which is setup on a small tripod pointing out my parents window.

On the server a cron is setup to run a script every 5 minutes. The script will determine if there is daylight enough outside to take a photo, and there is it will execute a gphoto2 command that will trigger the camera to take a photo and download the image to the computer. Once the image is on the computer it is then FTP’ed to my dedicated server for processing.

A cron is setup on my dedicated server for a script that checks an incoming folder for newly uploaded images. When a new image is found, it will process the image, creating several different file sizes, upload each file to Amazon S3 for storage and distribution through Amazon Cloudfront, and store a record of the image in a MySQL database.

Finally I have a web front end that reads from the database to display the latest photo, along with an archive of all the older photos that had been taken. Lets de-construct each step in the process to document how it all works.

Taking the Photo

The wonderful open source library gphoto2 does most of the work here. Gphoto2 allows you to control a camera in Linux via the command line. There is a large list of cameras on the gphoto2 website that are supported. Since I didn’t want to spend a lot of money on this project I bought an old Canon camera that was noted to work well with gphoto2.

On the mini computer at my parents a cron executes a PHP script every 5 minutes. The PHP script first checks to see if there are any other instances of gphoto2 running, if there are it exits. Next it determines at what time sunset and sunrise is, and if the time of day is between those two times as we don’t want to take photos of the darkness of night. Next the script checks to see if it is in the first 15 of sunrise, or last 15 minutes of sunset, if so we want to use a higher ISO on the camera to take the photo. Finally the gphoto2 script is called to take the photo.

Here is our cron entry:

*/5 * * * * /usr/bin/php /PATH/TO/BIN/bin/call-shoot-camera.php

Here is what my script looks like:

<?php
/**
 * Script to determine if it is light outside and whether to take a photo
 **/

// directory configuration
$base_dir = "/PATH/TO/HOME/FOLDER";
$archive_dir = $base_dir . "archive/".date("Y") . "/" . date("m") . "/" . date("d") . "/";

// check to see if gphoto2 is already running
$ps = `ps ua`;
if (strstr($ps, 'gphoto2')) {
    return 0;
}

// fifteen minutes in seconds
$fifteen_min = 900;

// setup directory for todays date
if (!is_file($archive_dir)) {
    `/bin/mkdir -p $archive_dir`;
}

// sunrise/sunset config
$zenith=96.8;
$long = -118.00737;
$lat = 49.8672;

$now = time();

$sunrise = date_sunrise($now, SUNFUNCS_RET_TIMESTAMP, $lat, $long, $zenith, -8);
$sunset = date_sunset($now, SUNFUNCS_RET_TIMESTAMP, $lat, $long, $zenith, -8);

$first_fifteen = $sunrise + $fifteen_min;
$second_fifteen = $sunrise + $fifteen_min + $fifteen_min;

$last_fifteen = $sunset - $fifteen_min;
$second_last_fifteen = $sunset - $fifteen_min - $fifteen_min;

// set the ISO higher if we are in the first 15 minutes of sunrise or last 15 minutes of sunset
if (($now >= $sunrise &#038;&#038; $now <= $first_fifteen) || ($now >= $last_fifteen &#038;&#038; $now <= $sunset)) {
    $iso = 2;
}
else {
    $iso = 1;
}

// take a photo if the time of day is between sunrise and sunset
if ($now >= $sunrise &#038;&#038; $now <= $sunset) {
    `/usr/bin/gphoto2 --set-config capturetarget=0 --set-config capture=1
--set-config imagesize="medium 1" --set-config aperture=4 --set-config iso=$iso
--set-config photoeffect=1 --capture-image-and-download
--filename "/PATH/TO/CAPTURE/capture/archive/%Y-%m-%d_%H:%M:%S.jpg"
--hook-script=/PATH/TO/BIN/bin/upload-and-set-new-photo.php`;
}

return 0;
?>

I will leave you to discover what all the flags do when calling the gphoto2 command, however would like to point out the –hook-script flag. What this flag does is call a script after the newly taken image has been downloaded from the camera to the computer. Thus we are able to call a second script that will upload our new photo to our server. This script is extremely basic and uses the standard linux FTP command.

<?php

if (getenv('ACTION') == 'download') {
    $file = getenv('ARGUMENT');
    $array = preg_split("/\//", $file);

    $final_file = array_pop($array);

    `/usr/bin/ftp -n -i -p HOSTNAME_OF_SERVER <<EOF
user FTPUSERNAME FTPPASSWORD
binary
put $file $final_file`;
}

As you can see, a really basic script that simply checks to see if the file was downloaded and if so to upload via ftp to our dedicated server.

I wanted to point out one final flag of gphoto2 before moving on to the dedicated server processing. An extremely handy flag when using gphoto2 with a new camera is the –list-config flag. This will tell you all the different config items of the camera you can set when using gphoto2.

Processing the Photo

On the dedicated server images are being uploaded to an incoming folder to be processed by another script. The processing script will scan the incoming folder looking for new images. Before processing an image, the script will check to make sure the image has not been written to within 20 seconds of the current time to make sure that the photo currently not being uploaded.

Once it is determined that the photo is not being uploaded we can process the image. The processing is done using the GD PHP extension, then uploaded to Amazon S3 using undesigned’s fantastic S3 PHP library. Finally the image information is stored in a MySQL database table.

Here is how the script looks:

<?php

// include our config file (contains db passwords and aws keys)
include_once("/PATH/TO/CONFIG/conf/config.inc");

// check if the incoming folder is already being processed
if (file_exists($cam_config['tmp_dir'] . 'process-incoming.pid')) {
    exit;
}
else {
    file_put_contents($cam_config['tmp_dir'] . 'process-incoming.pid', getmypid());
}

// libraries needed for s3 uploads and MySQL access
include_once($cam_config['base_dir'] . 'classes/s3-php5-curl/S3.php');
include_once($cam_config['base_dir'] . 'classes/db.cls');

$db = new db($cam_config['db_server'], $cam_config['db_user'], $cam_config['db_password'], $cam_config['db']);
$s3 = new S3($cam_config['aws_access_key'], $cam_config['aws_secret_key']);

// read all new files
$file_array = array();
if ($handle = opendir($cam_config['incoming_dir'])) {
    while (false !== ($file = readdir($handle))) {
        if ($file != "." &#038;&#038; $file != "..") {
            $file_array[] = $file;
        }
    }
    closedir($handle);
}

// get some exif info
foreach ($file_array as $file) {
    $file_full_path = $cam_config['incoming_dir'].$file;
    $file_base = basename($file, '.jpg');

    $filemtime = filemtime($file_full_path);

    $diff = time() - $filemtime;

    // skip any file that is still being written to
    if ($diff <= 20) {
        continue;
    }

    $exif = exif_read_data($file_full_path, 'File');

    $timestamp = $exif['FileDateTime'];

    $archive_dir = $cam_config['archive_dir'] . date("Y/m/d", $timestamp);

    if (!file_exists($archive_dir)) {
        `mkdir -p $archive_dir`;
    }

    $height = $exif['COMPUTED']['Height'];
    $width = $exif['COMPUTED']['Width'];
    // loop the different file sizes we want to create
    foreach ($cam_config['dir_array'] as $dir=>$new_width) {

        if ($dir == 'full') {
            // upload fullsize image to s3
            $s3->putObjectFile($file_full_path, $cam_config['bucket'], baseName($file_full_path), S3::ACL_PUBLIC_READ);
            `cp $file_full_path $archive_dir`;
        }
        else {
            // resize the image
            $new_height = ceil($new_width/$width * $height);
            $src = @imagecreatefromjpeg($file_full_path);
            $dst = @imagecreatetruecolor($new_width, $new_height);
            @imagecopyresampled($dst, $src, 0, 0, 0, 0, $new_width, $new_height, $width, $height);

            $new_file = $cam_config['tmp_dir'] . $file_base . '-' . $dir . '.jpg';
            @imagejpeg($dst, $new_file, 90);
            @imagedestroy($src);
            @imagedestroy($dst);

            // upload resized image to s3
            $s3->putObjectFile($new_file, $cam_config['bucket'], baseName($new_file), S3::ACL_PUBLIC_READ);
            `cp $new_file $archive_dir`;
        }

        // insert the photo into the database
        $picture_row = array(
            'cam_id'=>$cam_config['cam_id'],
            'timestamp'=>$timestamp,
            'filename'=>$file_base
        );

        $result = $db->createRow("picture", $picture_row);
    }

    `rm -f $file_full_path`;
    `rm -f {$cam_config['tmp_dir']}*.jpg`;
}

// remove the pid
unlink($cam_config['tmp_dir'] . 'process-incoming.pid');

With this script running on a cron we can now process any new file that gets uploaded to our server, upload it to Amazon S3, and log it in our database. With the photos now stored in the database we can easily setup a simple homepage to display the latest photo, and produce an archive of photos taken over time.

Summary

With the help of a few powerful open source programs and libraries and a small bit of hardware we are able to easily setup a camera that takes a photo every 5 minutes, and posts it to the Internet. You can view the webcam I setup at www.fauquiercam.com. In the future I will extend the processing further such that after every day, week, or month a time lapse is generated using mencoder.

http://alestic.com/2009/09/ec2-consistent-snapshot

How to Rotate EBS Snapshots

After using the ec2-consistent-snapshot script for a while I realized I would eventually need to find something to rotate these backups as they were growing out of control. Some of our volumes were having snapshots done every hour, and that was adding up quickly. Google provided me with no easy solution for rotating the snapshots, so I decided to write my own script.

Essentially what I wanted was to have a script that would rotate the snapshots in Grandfather-Father-Son type setup. I wanted to have hourly backups kept for 24 hours, daily kept for a week, weekly kept for a month, and monthly kept for a year. Anything older than that I don’t want, however the script can be tweaked to allow for older backups.

Basically what the script does is the following:

• Gets a list of all snapshots and puts them into an array indexed by the volume and the date the snapshot was taken
• For a given volume organize the snapshots so that there are only hourly snapshots for 1 day, daily snapshots for 1 week, weekly snapshots for 1 month, and monthly snapshots for 1 year and collect which snapshots require deleting.
• Delete the snapshots that are set for delete.

I wrote the script in PHP, mainly because it is what I feel most comfortable using. I am also once again using the Amazon PHP library. Here is the script in it’s entirety.

<?php
/*
 * rotate-ebs-snapshots.php
 *
 * Author: Stefan Klopp
 * Website: http://www.kloppmagic.ca
 * Requires: Amazon ec2 PHP Library
 *
 */

ini_set("include_path", ".:../:./include:../include:/PATH/TO/THIS/SCRIPT");

// include the amazon php library
require_once("Amazon/EC2/Client.php");
require_once("Amazon/EC2/Model/DeleteSnapshotRequest.php");

// include our configuration file with out ACCESS KEY and SECRET
include_once ('.config.inc.php');

$service = new Amazon_EC2_Client(AWS_ACCESS_KEY_ID,
                                       AWS_SECRET_ACCESS_KEY);

// setup our array of snapshots
$snap_array = setup_snapshot_array();

// call to rotate (you can call this for every volume you want to rotate)
rotate_standard_volume('VOLUME_ID_YOU_WISH_TO_ROTATE');

/*
 * Used to setup an array of all snapshots for a given aws account
 */
function setup_snapshot_array() {
    global $service;
    // Get a list of all EBS snapshots
    $response = $service->describeSnapshots($request);

    $snap_array = array();

    if ($response->isSetDescribeSnapshotsResult()) {
        $describeSnapshotsResult = $response->getDescribeSnapshotsResult();
        $snapshotList = $describeSnapshotsResult->getSnapshot();
        foreach ($snapshotList as $snapshot) {
            if ($snapshot->getStatus() == 'completed') {

                    // date is in the format of 2009-04-30T15:32:00.000Z
                    list($date, $time) = split("T", $snapshot->getStartTime());

                    list($year, $month, $day) = split("-", $date);
                    list($hour, $min, $second) = split(":", $time);

                    // convert the date to unix time
                    $time = mktime($hour, $min, 0, $month, $day, $year);

                    $new_row = array(
                            'snapshot_id'=>$snapshot->getSnapShotId(),
                            'volume_id'=>$snapshot->getVolumeId(),
                            'start_time'=>$time
                    );
                    // add to our array of snapshots indexed by the volume_id
                    $snap_array[$new_row['volume_id']][$new_row['start_time']] = $new_row;
            }
        }
    }

    // sort each volumes snapshots by the date it was created
    foreach ($snap_array as $vol=>$vol_snap_array) {
            krsort($vol_snap_array);
            $snap_array[$vol] = $vol_snap_array;
    }

    return($snap_array);
}

/*
 * Used to rotate the snapshots
 */
function rotate_standard_volume($vol_id) {
        global $snap_array, $service;

        // calculate the date ranges for snapshots
        $one_day = time() - 86400;
        $one_week = time() - 604800;
        $one_month = time() - 2629743;
        $one_year = time() - 31556926;

        $hourly_snaps = array();
        $daily_snaps = array();
        $weekly_snaps = array();
        $monthly_snaps = array();
        $delete_snaps = array();

        echo "Beginning rotation of volume: {$vol_id}\n";

        foreach($snap_array[$vol_id] as $time=>$snapshot) {

                echo "Testing snapshot {$snapshot['snapshot_id']} with a date of ".date("F d, Y @ G:i:s", $time)."... ";

                if ($time >=  $one_day) {
                        echo "Snapshot is within a day lets keep it.\n";
                        $hourly_snaps[$time] = $snapshot;
                }
                elseif ($time < $one_day &#038;&#038; $time >= $one_week) {
                        $ymd = date("Ymd", $time);
                        echo "Snapshot is daily {$ymd}.\n";

                        if (is_array($daily_snaps[$ymd])) {
                                echo "Already have a snapshot for {$ymd}, lets delete this snap.\n";
                                $delete_snaps[] = $snapshot;
                        }
                        else {
                                $daily_snaps[$ymd] = $snapshot;
                        }
                }
                elseif ($time < $one_week &#038;&#038; $time >= $one_month) {
                        $week = date("W", $time);
                        echo "Snapshot is weekly {$week}.\n";

                        if (is_array($weekly_snaps[$week])) {
                                echo "Already have a snapshot for week {$week}, lets delete this snap.\n";
                                $delete_snaps[] = $snapshot;
                        }
                        else {
                                $weekly_snaps[$week] = $snapshot;
                        }
                }
                elseif ($time < $one_month &#038;&#038; $time >= $one_year) {
                        $month = date("m", $time);
                        echo "Snapshot is monthly {$month}.\n";

                        if (is_array($monthly_snaps[$month])) {
                                echo "Already have a snapshot for month {$month}, lets delete this snap.\n";
                                $delete_snaps[] = $snapshot;
                        }
                        else {
                                $monthly_snaps[$month] = $snapshot;
                        }
                }
                else{
                        echo "Snapshot older than year old, lets delete it.\n";
                        $delete_snaps[] = $snapshot;
                }
        }

        foreach ($delete_snaps as $snapshot) {
                echo "Delete snapshot {$snapshot['snapshot_id']} with date ".date("F d, Y @ H:i", $snapshot['start_time'])." forever.\n";
                $request = new Amazon_EC2_Model_DeleteSnapshotRequest();
                $request->setSnapshotId($snapshot['snapshot_id']);
                $response = $service->deleteSnapshot($request);
        }
        echo "\n";
}

You can either run the script by editing the call to rotate_standard_volume. You can call this method for each volume you wish to rotate snapshots for. Also feel free to change the values of the date ranges to keep snapshots for a given date range for longer or shorter periods.

Finally to make this script effective you should have it run at least once a day via cron.

Conclusion

If you are like me and utilize EBS snapshots for backups of your data you will likely need to rotate those snapshots at some point. With the script above you should be able to quickly and easily rotate your snapshots. With a few tweaks you should be able to easily customize the rotation schedule to suit your needs.

The Architecture

For the rest of this post I am going to assume that we have two ec2 images we are using. The first image is our load balancer running HAProxy, this image is setup to forward incoming traffic to our second image, which is the application image. The application image will be setup with Amazon’s Auto Scaling to build scale up and down depending on the load of the instances. Lets assume our load balancer image has a AMI of ami-10000000 and our application image has an AMI of ami-20000000.

Auto Scaling Setup

The setup for the auto scaling will be pretty similar to what we did in the previous post. First we will setup a launch config:

as-create-launch-config auto-scaling-test --image-id ami-20000000 --instance-type c1.medium

Then we will create our auto scaling group:

as-create-auto-scaling-group auto-scaling-test --availability-zones us-east-1a --launch-configuration auto-scaling-test --max-size 4 --min-size 2

You will notice we ran this command without setting a load balancer. Since we are using HAProxy we do not need to set this up. Finally we will create our trigger for the scaling:

as-create-or-update-trigger auto-scaling-test --auto-scaling-group auto-scaling-test --measure CPUUtilization --statistic Average --period 60 --breach-duration 120 --lower-threshold 30 --lower-breach-increment"=-1" --upper-threshold 60 --upper-breach-increment 2

Once you have executed these commands, you will have 2 new application instances launched. This presents us with a problem, in order to send traffic to these instances we need to update the HAProxy config file so that it knows where to direct the traffic.

Updating HAProxy

In the following example I am going to show you how with the power of a simple script we can monitor for instances being launched or removed, and update HAProxy accordingly. I will be using S3 storage, PHP and the Amazon PHP Library to do this. You can use any programming language you prefer if you care to rewrite this code, the key is understanding what is going on.

In order for us to identify the running application instances we will need to know the AMI of the instance. We know our application instance has an AMI of ami-20000000. We could store this information straight into our script, however if we ever rebuilt the application instance, we would then have to update the script, which would then force us to have to rebuild our HAProxy instance. Not a lot of fun. What I like to do, is to store the AMI in S3. That way if I ever update my application instance, I can just change a small file in S3 and have my load balancer pick up those changes. Lets assume I stored the AMI of the application image in a file called ami-application and uploaded it to an S3 bucket so that it can be found at http://stefans-test-ami-bucket.s3.amazonaws.com/ami-application.

The Script

Basically what our script is going to do is the following:

• Get the AMI from S3 of our application image
• Get a list of all running instances from Amazon, and log which ones match our application image
• Get a default config file for HAProxy
• Append the IP addresses of the running application instances to the config file
• Compare the new config file to the old config file, if they are the same no action is needed, if they are different, replace the haproxy.cfg and restart the server

Our default config file for HAProxy will essentially be the full config without any server directives in the backend section. For example, our default config file could look something like:

global
        log 127.0.0.1   local0
        log 127.0.0.1   local1 notice
        maxconn 50000
        user haproxy
        group haproxy
        daemon
        chroot /var/chroot/haproxy

defaults
        log       global
        mode    tcp
        option   httplog
        option   forwardfor
        retries   2
        redispatch
        maxconn       50000
        timeout connect    10000
        timeout client        30000
        timeout server       60000
        stats uri /ha_stats
        stats realm Global\ statistics
        stats auth myusername:mypassword

frontend www *:80
        maxconn 40000
        mode http
        default_backend www_farm

backend www_farm
        mode http
        balance roundrobin

Now that we have our default config file, all we have to do to generate our HAProxy config is to add a server line to the end of it for each instance we have running. Lets look at the PHP code to do that:

<?php
// setup our include path, this is needed since the script is run from cron
ini_set("include_path", ".:../:./include:../include:/path/to/this/script/update-haproxy");

// including the Amazon EC2 PHP Library
require_once("Amazon/EC2/Client.php");

// include the config file containing your AWS Access Key and Secret
include_once ('.config.inc.php');

// location of AMI of the application image
$ami_location = 'http://stefans-test-ami-bucket.s3.amazonaws.com/ami-application';
$ami_id = chop(file_get_contents($ami_location));

// connect to Amazon and pull a list of all running instances
$service = new Amazon_EC2_Client(AWS_ACCESS_KEY_ID,
                                       AWS_SECRET_ACCESS_KEY);

$response = $service->describeInstances($request);

$describeInstancesResult = $response->getDescribeInstancesResult();
$reservationList = $describeInstancesResult->getReservation();

// loop the list of running instances and match those that have an AMI of the application image
$hosts = array();
foreach ($reservationList as $reservation) {
        $runningInstanceList = $reservation->getRunningInstance();
        foreach ($runningInstanceList as $runningInstance) {
                $ami = $runningInstance->getImageId();

                $state = $runningInstance->getInstanceState();

                if ($ami == $ami_id &#038;&#038; $state->getName() == 'running') {

                        $dns_name = $runningInstance->getPublicDnsName();

                        $app_ip = gethostbyname($dns_name);

                        $hosts[] = $app_ip;
                }
        }
}

// get our default HAProxy configuration file
$haproxy_cfg = file_get_contents("/share/etc/.default-haproxy.cfg");

foreach ($hosts as $i=>$ip) {
        $haproxy_cfg .= '
        server server'.$i.' '.$ip.':80 maxconn 250 check';
}
// test if the configs differ
$current_cfg = file_get_contents("/path/to/haproxy.cfg");
if ($current_cfg == $haproxy_cfg) {
        echo "everything is good, configs are the same.\n";
}
else {
        echo "file out of date, updating.\n";
        file_put_contents('/path/to/this/script/.latest-haproxy.cfg', $haproxy_cfg);
        system("cp /path/to/this/script/.latest-haproxy.cfg /path/to/haproxy.cfg");
        system("/etc/init.d/haproxy reload");
}
?>

I think this script is pretty self explanatory, and does what we outlined as our goals for it above. If you ran the script from command line your HAProxy config file would get updated, and the server would be restarted.

Now that we have our working script, the last thing we need to do is setup this script to run on cron. I find updating every 2-5 minutes is sufficient to keep your config updated for auto scaling.

One of the nice benefits of having this script is it allows you the ability to easily pre-scale your solution if you know you are going to receive a big traffic spike. All you have to do is launch as many new instances of your application image and the script will manage the setup of HAProxy for you.

Conclusion

With under 100 lines of code and a few tools we were able to setup a script to keep the HAProxy config file up to date with your running application instances. This allows us the ability to use HAProxy instead of Amazon Load Balancing, but still get to have all the benefits of Auto Scaling. Lastly it is to note this script is just an example, and should be tailored to your own environment as you see fit. It is also best to store this script, and the default HAProxy config in a EBS volume if possible, as it will save you from having to rebuild your instance.

Creating an Auto Scaling Launch Config

The first step in setting up Auto Scaling is to create a launch config. The launch config is used to determine what ec2 image, and size (small, medium, etc) will be used to setup a new instance for your Auto Scaling group. To setup a launch config you will call the as-create-launch-config. For example to create a new launch config called auto-scaling-test that would launch the image ami-12345678 of size c1.medium you would run the following command:


as-create-launch-config auto-scaling-test --image-id ami-12345678 --instance-type c1.medium


Create an Auto Scaling Group

The next step to enabling Auto Scaling is to setup an Auto Scaling Group. An Auto Scaling group tells Amazon what zones you want your instances created in, the minimum and maximum number of instances to ever launch, and which launch config to utilize. To create an Auto Scaling group you will call the as-create-auto-scaling-group command. For example if you wanted to create a new group with a name of auto-scaling-test using the availability zones of us-east-1a with a minimum number of instances being 2 and a maximum of 4 using our newly created launch config you would run:


as-create-auto-scaling-group auto-scaling-test --availability-zones us-east-1a --launch-configuration auto-scaling-test --max-size 4 --min-size 2


When this command is executed 2 new instances will be created as per the directions of the launch config. the as-create-auto-scaling-group can also take be linked to a load balancer. Thus if we wanted to have this group setup with the load balancer we created in the previous article, you would run:


as-create-auto-scaling-group auto-scaling-test --availability-zones us-east-1a --launch-configuration auto-scaling-test --max-size 4 --min-size 2 --load-balancers test-balancer


After execution this would setup 2 new instances as per the instructions of the launch config, and register these instances with the load balancer test-balancer.

Creating Auto Scaling Triggers

Triggers are used by Auto Scaling to determine whether to launch or terminate instances within an Auto Scaling Group. To setup a trigger you will use the as-create-or-update-trigger command. Here is an example using the auto scaling group we created earlier:


as-create-or-update-trigger auto-scaling-test --auto-scaling-group auto-scaling-test --measure CPUUtilization --statistic Average --period 60 --breach-duration 120 --lower-threshold 30 --lower-breach-increment"=-1" --upper-threshold 60 --upper-breach-increment 2


Lets walk through what this command is doing. Basically what this command is saying is, create a new trigger called auto-scaling-test. This trigger should use the auto-scaling group called auto-scaling-test. It should measure the average CPU utilization of the current instances in the auto scaling group every 60 seconds. If the CPU utilization goes over 60% over the period of 120 seconds launch 2 new instances. Alternatively if the CPU utilization drops below 30% over the period of 120 seconds terminate 1 of the instances. Remember that the trigger will never terminate more instances than the minimum number of instances and it will not launch more instances than the maximum number of instances as defined in the Auto Scaling Group.

Shutting Down an Auto Scaling Group

Initially shutting down an Auto Scaling group can be a bit tricky as you cannot delete an Auto Scaling Group until all the instances are terminated or deregistered from the group. The best way to terminate an Auto Scaling group, it’s triggers and launch config is to do the following steps:

• Delete all triggers
• Update the Auto Scaling group to have a minimum and maximum number of instances of 0
• Wait for the instances registered with the Auto Scaling group to be terminated
• Delete the Auto Scaling group
• Delete the launch config

To do this with the examples we used above we would issue the following commands:


as-delete-trigger auto-scaling-test --auto-scaling-group auto-scaling-test

as-update-auto-scaling-group auto-scaling-test --min-size 0 -max-size 0

as-delete-auto-scaling-group auto-scaling-test

as-delete-launch-config auto-scaling-test


With those 4 commands you can easily delete your Auto Scaling group as well as any launch configs or triggers that are associated with it.

Conclusion

Auto Scaling provides an easy and efficient way to grow and shrink your hosting solution based on your current traffic. In events where you are hit with unexpected traffic Auto Scaling can provide a failsafe by automatically launching new instances and scaling up your solution to meet this new traffic. When the traffic subsides Auto Scaling will scale down your solution so that you are not wasting money by running more instances than you require.

One thing to note is that if you know before hand that you will be receiving a traffic spike at a specific time, it may be more benefitial to launch new instances manually before the spike. This will save your system from getting hammered before having the Auto Scaling launches new instances to cope with the additional load. If you rely on Auto Scaling alone in this scenario you could see many requests at the start of the heavy traffic timeout or fail as the minimum number of instances likely won’t be able to handle the traffic load.

Elastic Load Balancing vs HAProxy

Elastic Load Balancing (ELB) was introduced by Amazon Web Services in May of 2009. Elastic Load Balancing distributes traffic across multiple EC2 instances and scales up as your traffic increases. This all sounds like a perfect solution for your load balancing. However it does present a few issues. The rate at which ELB scales up is often a little slow. This means that if your website typically does not get a lot of traffic, when it does it a giant spike it will likely take the load balancer some time to catch up to the demand of the new traffic. If your traffic increases are more gradual however, ELB appears to scale up a lot smoother. For more information on tests of Elastic Load Balancing’s performance see this article:

http://agiletesting.blogspot.com/2010/04/load-balancing-in-cloud-whitepaper-by.html

HAProxy on the other hand will handle large traffic spikes very handily. In addition HAProxy gives you the power to fine tune your load balancing, as well as additional features such as error pages, real time statistics, and the use of acl’s. However not everyone requires these features, so you will need to decide for yourself if you want to go with the easy solution, or the more robust route. I will describe how you can setup Elastic Load Balancing, as well as how to auto scale with ELB or by using HAProxy.

Setting Up Elastic Load Balancing

Setting up Elastic Load Balancing is as easy as running a single command using the Amazon API Tools. To create a new load balancer you will run the elb-create-lb command. When you run the command you will specify the name of the new load balancer, the availability zones you want to use, the incoming port and the protocol to use for it, and the port the traffic should be sent to on the instance. For example if we want to create a new load balancer called test-balancer, in the us-east-1a zone, that is listening on port 80 for http traffic, and will send traffic to port 80 on our instances we would run:


elb-create-lb test-balancer --availability-zones us-east-1a --listener "lb-port=80,instance-port=80,protocol=http"


Executing this command will return the DNS name of the new load balancer that was created. You will use this DNS name to point traffic to so that it gets distributed by your load balancing. Unfortunately the recommended way to point this traffic is via a DNS CNAME. The reason this is a problem is that you cannot use a CNAME with a root domain. For example I would not be able to point kloppmagic.ca to the load balancer. I could however point www.kloppmagic.ca. Using a sub domain appears to be the common work around people are utilizing. The other option is to do a lookup of the DNS name returned from the command and using the IP address. This approach you will constantly have to monitor the DNS name from Amazon however, as they are not utilizing static IP’s for load balancing.

Once you have load balancer setup you will need to associate running EC2 instances with the load balancer. To do this you will run the command elb-register-instances-with-lb. This command allows you to register an instance with a specific load balancer. For example if we had 2 instances with instance id’s of i-123456 and i-123457 that you wanted to associate with the test-balancer load balancer you would run:


elb-register-instances-with-lb test-balancer --instances i-123456 i-123457


In the same manor you can use the elb-deregister-instances-with-lb to remove instances from a given load balancer. Finally if you wish to view all the load balancers you currently have setup you can utilize the elb-describe-lbs

Ultimate it is that easy to setup load balancing with Amazon Web Services. If you do not require all the features of HAProxy, and want something quick and easy to setup, Elastic Load Balancing cannot be beat.