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Blacklisting DNS Server on Amazon EC2

Amazon EC2 is a great resource for cheap virtual servers to do simple things, like DNS or (low bandwidth) VPNs. I had the need this morning to set up a DNS server for a company which needed to blacklist a list of domains. The simplest way to do this is by editing all the computers’ hostfiles, but that method leaves a lot to be desired. Namely, blocking entire domains (as opposed to single subdomains), and deploying changes. Centralizing in a single place makes the job instant, immediate, and in the end, faster.

The following are the steps I used to set this up on an EC2 server. All command line instructions are followed by a single command you can run to execute the step. There is a full script below, at the end of the post, containing all steps from when you first login to SSH ("Login to root") to the end.


I am not going to go into the details of setting up an EC2 instance, as that information can be found elsewhere. I will also be skipping over some of the more obvious steps. Just create a default EC2 instance with the “Amazon Linux AMI”, and I will list all the changes that need to be made beyond that.

  • Creating the instance
    • For the first year, for the instance type, you might as well use a t2.micro, as it is free. After that, a t2.nano (which is a new lower level) currently at $56.94/year ($0.0065/Hour), should be fine.
    • After you select your instance type, click “Review and Launch” to launch the instance with all of the defaults.
    • After the confirmation screen, it will ask you to create a key pair. You can see other tutorials about this and how it enables you to log into your instance.
  • Edit the security group
    • Next, you need to edit the security group for your instance to allow incoming connections.
    • Go to “Instances” under the “Instances” group on the left menu, and click your instance.
    • In the bottom of the window, in the “Descriptions” tab, click the link next to “Security Groups”, which will bring you to the proper group in the security groups tab.
    • Right click it and “Edit inbound Rules”.
    • Make sure it has the following rules with Source=Anywhere: ALL ICMP [For pinging], SSH, HTTP, DNS (UDP), DNS (TCP)
  • Assign a permanent IP to your instance
    • To do this, click the “Elastic IPs” under “Network & Security” in the left menu.
    • Click “Allocate New Address”.
    • After creating it, right click the new address, then “Associate Address”, and assign it to your new instance.
  • You should probably set this IP up as an A record somewhere. I will refer to this IP as dns.yourdomain.com from now on.
  • Login to root
    • SSH into your instance as the ec2-user via “ssh ec2-user@dns.yourdomain.com”. If in windows, you could also use putty.
    • Sudo into root via “sudo su”.
  • Allow root login
    • At this point, I recommend setting it up so you can directly root into the server. Warning: some people consider this a security risk.
    • Copy your key pair(s) to the root user via “cat /home/ec2-user/.ssh/authorized_keys > /root/.ssh/authorized_keys
    • Set SSHD to permit root logins by changing the PermitRootLogin variable to “yes” in /etc/ssh/sshd_config. A quick command to do this is “perl -pi -e 's/^\s*#?\s*PermitRootLogin.*$/PermitRootLogin yes/igm' /etc/ssh/sshd_config”, and then reload the SSHD config with “service sshd reload”. Make sure to attempt to directly log into SSH as root before exiting your current session to make sure you haven’t locked yourself out.
  • Install apache (the web server), bind/named (the DNS server), and PHP (a scripting language)
    • yum -y install bind httpd php
  • Start and set services to run at boot
    • service httpd start; service named start; chkconfig httpd on; chkconfig named on;
  • Set the DNS server to be usable by other computers
    • Edit /etc/named.conf and change the 2 following lines to have the value “any”: “listen-on port 53” and “allow-query”
    • perl -pi -e 's/^(\s*(?:listen-on port 53|allow-query)\s*{).*$/$1 any; };/igm' /etc/named.conf; service named reload;
  • Point the DNS server to the blacklist files
    • This is done by adding “include "/var/named/blacklisted.conf";” to /etc/named.conf
    • echo -ne '\ninclude "/var/named/blacklisted.conf";' >> /etc/named.conf
  • Create the blacklist domain list file
    • touch /var/named/blacklisted.conf
  • Create the blacklist zone file
    • Put the following into /var/named/blacklisted.db . Make sure to change dns.yourdomain.com to your domain (or otherwise, “localhost”), and 1.1.1.1 to dns.yourdomain.com’s (your server’s) IP address. Make sure to keep all periods intact.
      $TTL 14400
      @       IN SOA dns.yourdomain.com. dns.yourdomain.com ( 2003052800  86400  300  604800  3600 )
      @       IN      NS   dns.yourdomain.com.
      @       IN      A    1.1.1.1
      *       IN      A    1.1.1.1
    • The first 2 lines tell the server the domains belong to it. The 3rd line sets the base blacklisted domain to your server’s IP. The 4th line sets all subdomains of the blacklisted domain to your server’s IP.
    • This can be done via (Update the first line with your values)
      YOURDOMAIN="dns.yourdomain.com"; YOURIP="1.1.1.1";
      echo -ne "\$TTL 14400\n@       IN SOA $YOURDOMAIN. $YOURDOMAIN ( 2003052800  86400  300  604800  3600 )\n@       IN      NS   $YOURDOMAIN.\n@       IN      A    $YOURIP\n*       IN      A    $YOURIP" > /var/named/blacklisted.db;
  • Fix the permissions on the blacklist files
    • chgrp named /var/named/blacklisted.*; chmod 660 /var/named/blacklisted.*;
  • Set the server’s domain resolution name servers
    • The server always needs to look at itself before other DNS servers. To do this, comment out everything in /etc/resolv.conf and add to it “nameserver localhost”. This is not the best solution. I’ll find something better later.
    • perl -pi -e 's/^(?!;)/;/gm' /etc/resolv.conf; echo -ne '\nnameserver localhost' >> /etc/resolv.conf
  • Run a test
    • At this point, it’s a good idea to make sure the DNS server is working as intended. So first, we’ll add an example domain to the DNS server.
    • Add the following to /var/named/blacklisted.conf and restart named to get the server going with example.com: “zone "example.com" { type master; file "blacklisted.db"; };
    • echo 'zone "example.com" { type master; file "blacklisted.db"; };' >> /var/named/blacklisted.conf; service named reload;
    • Ping “test.example.com” and make sure it’s IP is your server’s IP
    • Set your computer’s DNS to your server’s IP in your computer’s network settings, ping “test.example.com” from your computer, and make sure the returned IP is your server’s IP. If it works, you can restore your computer’s DNS settings.
  • Have the server return a message when a blacklisted domain is accessed
    • Add your message to /var/www/html
    • echo 'Domain is blocked' > /var/www/html/index.html
    • Set all URL paths to show the message by adding the following to the /var/www/html/.htaccess file
      RewriteEngine on
      RewriteCond %{REQUEST_URI} !index.html
      RewriteCond %{REQUEST_URI} !AddRules/
      RewriteRule ^(.*)$ /index.html [L]
    • echo -ne 'RewriteEngine on\nRewriteCond %{REQUEST_URI} !index.html\nRewriteCond %{REQUEST_URI} !AddRules/\nRewriteRule ^(.*)$ /index.html [L]' > /var/www/html/.htaccess
    • Turn on AllowOverride in the /etc/httpd/conf/httpd.conf for the document directory (/var/www/html/) via “ perl -0777 -pi -e 's~(<Directory "/var/www/html">.*?\n\s*AllowOverride).*?\n~$1 All~s' /etc/httpd/conf/httpd.conf
    • Start the server via “service httpd graceful
  • Create a script that allows apache to refresh the name server’s settings
    • Create a script at /var/www/html/AddRules/restart_named with “/sbin/service named reload” and set it to executable
    • mkdir /var/www/html/AddRules; echo '/sbin/service named reload' > /var/www/html/AddRules/restart_named; chmod 755 /var/www/html/AddRules/restart_named
    • Allow the user to run the script as root by adding to /etc/sudoers “apache ALL=(root) NOPASSWD: /var/www/html/AddRules/restart_named” and “Defaults!/var/www/html/AddRules/restart_named !requiretty
    • echo -e 'apache ALL=(root) NOPASSWD:/var/www/html/AddRules/restart_named\nDefaults!/var/www/html/AddRules/restart_named !requiretty' >> /etc/sudoers
  • Create a script that allows the user to add, remove, and list the blacklisted domains
    • Add the following to /var/www/html/AddRules/index.php (one line command not given. You can use “nano” to create it)
      <?php
      //Get old domains
      $BlockedFile='/var/named/blacklisted.conf';
      $CurrentZones=Array();
      foreach(explode("\n", file_get_contents($BlockedFile)) as $Line)
              if(preg_match('/^zone "([\w\._-]+)"/', $Line, $Results))
                      $CurrentZones[]=$Results[1];
      
      //List domains
      if(isset($_REQUEST['List']))
              return print implode('<br>', $CurrentZones);
      
      //Get new domains
      if(!isset($_REQUEST['Domains']))
              return print 'Missing Domains';
      $Domains=$_REQUEST['Domains'];
      if(!preg_match('/^[\w\._-]+(,[\w\._-]+)*$/uD', $Domains))
              return print 'Invalid domains string';
      $Domains=explode(',', $Domains);
      
      //Remove domains
      if(isset($_REQUEST['Remove']))
      {
              $CurrentZones=array_flip($CurrentZones);
              foreach($Domains as $Domain)
                      unset($CurrentZones[$Domain]);
              $FinalDomainList=array_keys($CurrentZones);
      }
      else //Combine domains
              $FinalDomainList=array_unique(array_merge($Domains, $CurrentZones));
      
      //Output to the file
      $FinalDomainData=Array();
      foreach($FinalDomainList as $Domain)
              $FinalDomainData[]=
                      "zone \"$Domain\" { type master; file \"blacklisted.db\"; };";
      file_put_contents($BlockedFile, implode("\n", $FinalDomainData));
      
      //Reload named
      print `sudo /var/www/html/AddRules/restart_named`;
      ?>
    • Add the “apache” user to the “named” group so the script can update the list of domains in /var/named/blacklisted.conf via “usermod -a -G named apache; service httpd graceful;
  • Run the domain update script
    • To add a domain (separate by commas): http://dns.yourdomain.com/AddRules/?Domains=domain1.com,domain2.com
    • To remove a domain (add “Remove&” after the “?”): http://dns.yourdomain.com/AddRules/?Remove&Domains=domain1.com,domain2.com
    • To list the domains: http://dns.yourdomain.com/AddRules/?List
  • Password protect the domain update script
    • Add to AddRules/.htaccess the following
      AuthType Basic
      AuthName "Admins Only"
      AuthUserFile "/var/www/html/AddRules/.htpasswd"
      require valid-user
    • echo -ne 'AuthType Basic\nAuthName "Admins Only"\nAuthUserFile "/var/www/html/AddRules/.htpasswd"\nrequire valid-user' > /var/www/html/AddRules/.htaccess
    • Warning: Putting the password file in an http accessible directory is a security risk. I just did this for sake of organization.
    • Create the user+password via “htpasswd -bc /var/www/html/AddRules/.htpasswd USERNAME” and then entering the password


[Edit on 2016-01-30 @ noon]

To permanently set “localhost” as the resolver DNS, add “DNS1=localhost” to “/etc/sysconfig/network-scripts/ifcfg-eth0”. I have not yet confirmed this edit.

Security Issue

Soon after setting up this DNS server, it started getting hit by a DNS amplification attack. As the server is being used as a client’s DNS server, turning off recursion is not available. The best solution is to limit the people who can query the name server via an access list (usually a specific subnet), but that would very often not be an option either. The solution I currently have in place, which I have not actually verified if it works, is to add a forced-forward rule which only makes external requests to the name server provided by Amazon. To do this, get the name server’s IP from /etc/resolv.conf (it should be commented from an earlier step). Then add the following to your named.conf in the “options” section.

	forwarders {
		DNS_SERVER_IP;
	};
	forward only;

After I added this rule, external DNS requests stopped going through completely. To fix this, I turned “dnssec-validation” to “no” in the named.conf. Don’t forget to restart the service once you have made your changes.

[End of edit]

Full serverside script
Make sure to run this as root (login as root or sudo it)

Download the script here. Make sure to chmod and sudo it when running. “chmod +x dnsblacklist_install.sh; sudo ./dnsblacklist_install.sh;

#User defined variables
VARIABLES_SET=0; #Set this to 1 to allow the script to run
YOUR_DOMAIN="localhost";
YOUR_IP="1.1.1.1";
BLOCKED_ERROR_MESSAGE="Domain is blocked";
ADDRULES_USERNAME="YourUserName";
ADDRULES_PASSWORD="YourPassword";

#Confirm script is ready to run
if [ $VARIABLES_SET != 1 ]; then
    echo 'Variables need to be set in the script';
    exit 1;
fi
if [ `whoami` != 'root' ]; then
    echo 'Must be root to run script. When running the script, add "sudo" before it to' \
        'run as root';
    exit 1;
fi

#Allow root login
cat /home/ec2-user/.ssh/authorized_keys > /root/.ssh/authorized_keys;
perl -pi -e 's/^\s*#?\s*PermitRootLogin.*$/PermitRootLogin yes/igm' /etc/ssh/sshd_config;
service sshd reload;

#Install services
yum -y install bind httpd php;
chkconfig httpd on;
chkconfig named on;
service httpd start;
service named start;

#Set the DNS server to be usable by other computers
perl -pi -e 's/^(\s*(?:listen-on port 53|allow-query)\s*{).*$/$1 any; };/igm' \
    /etc/named.conf;
service named reload;

#Create/link the blacklist files
echo -ne '\ninclude "/var/named/blacklisted.conf";' >> /etc/named.conf;
touch /var/named/blacklisted.conf;

#Create the blacklist zone file
echo -ne "\$TTL 14400
@       IN SOA $YOUR_DOMAIN. $YOUR_DOMAIN ( 2003052800  86400  300  604800  3600 )
@       IN      NS   $YOUR_DOMAIN.
@       IN      A    $YOUR_IP
*       IN      A    $YOUR_IP" > /var/named/blacklisted.db;

#Fix the permissions on the blacklist files
chgrp named /var/named/blacklisted.*;
chmod 660 /var/named/blacklisted.*;

#Set the server’s domain resolution name servers
perl -pi -e 's/^(?!;)/;/gm' /etc/resolv.conf;
echo -ne '\nnameserver localhost' >> /etc/resolv.conf;

#Run a test
echo 'zone "example.com" { type master; file "blacklisted.db"; };' >> \
    /var/named/blacklisted.conf;
service named reload;
FOUND_IP=`dig -t A example.com | grep -ioP "^example\.com\..*?"'in\s+a\s+[\d\.:]+' | \
     grep -oP '[\d\.:]+$'`;
if [ "$YOUR_IP" == "$FOUND_IP" ]
then
  echo 'Success: Example domain matches your given IP' > /dev/stderr;
else
  echo 'Warning: Example domain does not match your given IP' > /dev/stderr;
fi

#Have the server return a message when a blacklisted domain is accessed
echo "$BLOCKED_ERROR_MESSAGE" > /var/www/html/index.html;
perl -0777 -pi -e 's~(<Directory "/var/www/html">.*?\n\s*AllowOverride).*?\n~$1 All~s' \
     /etc/httpd/conf/httpd.conf;
echo -n 'RewriteEngine on
RewriteCond %{REQUEST_URI} !index.html
RewriteCond %{REQUEST_URI} !AddRules/
RewriteRule ^(.*)$ /index.html [L]' > /var/www/html/.htaccess;
service httpd graceful;

#Create a script that allows apache to refresh the name server’s settings
mkdir /var/www/html/AddRules;
echo '/sbin/service named reload' > /var/www/html/AddRules/restart_named;
chmod 755 /var/www/html/AddRules/restart_named;

echo 'apache ALL=(root) NOPASSWD:/var/www/html/AddRules/restart_named
Defaults!/var/www/html/AddRules/restart_named !requiretty' >> /etc/sudoers;

#Create a script that allows the user to add, remove, and list the blacklisted domains
echo -n $'<?php
//Get old domains
$BlockedFile=\'/var/named/blacklisted.conf\';
$CurrentZones=Array();
foreach(explode("\\n", file_get_contents($BlockedFile)) as $Line)
        if(preg_match(\'/^zone "([\\w\\._-]+)"/\', $Line, $Results))
                $CurrentZones[]=$Results[1];

//List domains
if(isset($_REQUEST[\'List\']))
        return print implode(\'<br>\', $CurrentZones);

//Get new domains
if(!isset($_REQUEST[\'Domains\']))
        return print \'Missing Domains\';
$Domains=$_REQUEST[\'Domains\'];
if(!preg_match(\'/^[\\w\\._-]+(,[\\w\\._-]+)*$/uD\', $Domains))
        return print \'Invalid domains string\';
$Domains=explode(\',\', $Domains);

//Remove domains
if(isset($_REQUEST[\'Remove\']))
{
        $CurrentZones=array_flip($CurrentZones);
        foreach($Domains as $Domain)
                unset($CurrentZones[$Domain]);
        $FinalDomainList=array_keys($CurrentZones);
}
else //Combine domains
        $FinalDomainList=array_unique(array_merge($Domains, $CurrentZones));

//Output to the file
$FinalDomainData=Array();
foreach($FinalDomainList as $Domain)
    $FinalDomainData[]="zone \\"$Domain\\" { type master; file \\"blacklisted.db\\"; };";
file_put_contents($BlockedFile, implode("\\n", $FinalDomainData));

//Reload named
print `sudo /var/www/html/AddRules/restart_named`;
?>' > /var/www/html/AddRules/index.php;

usermod -a -G named apache;
service httpd graceful;

#Password protect the domain update script
echo -n 'AuthType Basic
AuthName "Admins Only"
AuthUserFile "/var/www/html/AddRules/.htpasswd"
require valid-user' > /var/www/html/AddRules/.htaccess;

htpasswd -bc /var/www/html/AddRules/.htpasswd "$ADDRULES_USERNAME" "$ADDRULES_PASSWORD";

echo 'Script complete';
Syncing Amazon EC2 Instances

In continuation of yesterday’s post, in which I showed how to create Amazon AMIs to keep your newly created EC2 instances up to date, today I will cover syncing already-live instances from the master to slaves. All of the below takes place on the master instance, and assumes all other instances are part of the slave group. You may have to use extra filters on the below “aws” command to only pull IPs from a certain group of instances.

Here is a simple bash script (hereby referred to as “Propagate.sh”) which syncs /var/www/html/ to all of your slave instances. It uses the “aws” command line interface provided by Amazon, which comes default with the Amazon Linux starter AMI.

#The first command line of the script contains the master’s IP, so it does not sync with itself.
export LocalIP=Your_Master_IP_Here;

#Get the IPs of all slave instances
export NewIPs=`aws ec2 describe-instances | grep '"PrivateIpAddress"' | perl -i -pe 's/(^.*?: "|",?\s*?$)//gm' | sort -u | grep -v $LocalIP`

#Loop over all slave instances
for i in $NewIPs; do
        echo "Syncing to: $i";
        #Run an rsync from the master to the slave
        rsync -aP -e 'ssh -o StrictHostKeyChecking=no' /var/www/html/ root@$i:/var/www/html/;
done

You may also want to add “-o UserKnownHostsFile=/dev/null” to the SSH command (directly after “-o StrictHostKeyChecking=no”), as a second EC2 instance may end up having the same IP as a previously terminated instance. Another solution to that problem is syncing the “/etc/ssh/ssh_host_rsa_key*” from the master when an instance initializes, so all instances keep the same SSH fingerprint.


To let other people manually execute this script, you can create a PHP file with the following in it. (Change /var/www/ in all below examples to where you place your Propagate.sh)

<? print nl2br(htmlentities(shell_exec('sudo /var/www/Propagate.sh 2<&1'))); ?>

If your Propagate.sh needs to be ran as root, which it may if your PHP environment is not run as the user root (usually “apache”), then you need to make sure it CAN run as root without intervention. To do this, add the following to the /etc/sudoers file
apache  ALL=(ALL)       NOPASSWD: /usr/bin/whoami, /var/www/Propagate.sh
Change the user from “apache” to the user which PHP runs as (when running through apache).
I included “whoami” as a valid sudoer application for testing purposes.
Also, in the sudoers file, if “Defaults requiretty” is turned on, you will need to comment it/turn it off.

While I did not mention it in yesterday's post, I thought I should at least mention it here. There are other ways to keep file systems in sync with each other. This is just a good use case for when you want to keep all instances as separate independent entities. Another solution to many of the previously mentioned problems is using Amazon's new EFS, which is currently still in preview mode.

Custom Initializations for Amazon AMIs

I was recently hired to move a client's site from our primary server in Houston to the Amazon cloud, as it was about to take a big hit in traffic. The normal setup for this kind of job is pretty straightforward. Move the database over to RDS, set up an AMI of an EC2 instance, a load balancer, and ec2 auto scaling. However, there were a couple of problems I needed to solve this time around for the instances launched via the auto scalar that I had not really needed to do before. This includes syncing the SSH settings and current codebase from the primary instance, as opposed to recreating AMIs every time there was a change. So, long story short, here are the problems and solutions that need to be added before the AMI image is created.


This all assumes you are running as root. Most of these commands should work on any Linux distribution that Amazon has default AMIs for, but some of these may only work in the Amazon and CentOS AMIs.


Pre-setup:
  • Your first instance that you are creating the AMI from should be a permanent instance. This is important for 2 reasons.
    1. When changing configurations for the auto scalar, if and when your instances are terminated and recreated, this instance will always be available on the load balancer, so there is no downtime.
    2. This instance can act as a central repository for other instances to sync from.
    So make sure this instance has an elastic IP assigned to it. From here on out, we will refer to this instance as PrimaryInstance (you can set this physically in the host file, or change it in all scripts to however you want to refer to your elastic IP [most likely through a DNS domain]).
  • Create your ssh private key for the instances: (For all prompts, use default settings)
    ssh-keygen -t rsa -b 4096 -C "your_email@example.com"
  • Make sure your current ssh authorized_keys contains your new ssh private key:
    cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys
  • Make sure your ssh known_hosts includes your primary instance, so all future ssh calls to it are automatically accept it as a known host:
    ssh PrimaryInstance -o StrictHostKeyChecking=no
    You do not have to finish the login process. This just makes sure our primary instance will be recognized by other instances.
  • Turn on PermitRootLogin in /etc/ssh/sshd_config and reload the sshd config service sshd reload
    I just recommend this because it makes life way, way easier. The scripts below assume that you did this.

Create a custom init file that runs on boot to take care of all the commands that need to be run.
#Create the script and make sure the full path (+all other root environment variables) are set when it is ran
echo '#!/bin/bash -l' > /etc/rc.d/init.d/custom_init

#Set the script as executable
chmod +x /etc/rc.d/init.d/custom_init

#Executes it as one of the last scripts on run level 3 (Multi-user mode with networking)
ln -s ../init.d/custom_init /etc/rc.d/rc3.d/S99custom_init
All of the below commands in this post will go into this script.

Allow login via password authentication:
perl -i -pe 's/^PasswordAuthentication.*$/PasswordAuthentication yes/mg' /etc/ssh/sshd_config
service sshd reload
Notes:
You may not want to do this. It was just required by my client in this case.
This is required in the startup script because Amazon likes to mess with the sshd_config (and authorized_keys) in new instances it boots.

Sync SSH settings from the PrimaryInstance:
#Remove the known_hosts file, in case something on the PrimaryInstance has changed that would block ssh commands.
rm -f ~/.ssh/known_hosts

#Sync the SSH settings from the PrimaryInstance
rsync -e 'ssh -o StrictHostKeyChecking=no' -a root@PrimaryInstance:~/.ssh/ ~/.ssh/

Sync required files from the PrimaryInstance. In this case, the default web root folder:
rsync -at root@PrimaryInstance:/var/www/html/ /var/www/html/

That's it for the things that need to be configured/added to the instance. From there, create your AMI and launch config, and create/modify your launch group and load balancer.


Also, as a very important note about your load balancer, make sure if you are mirroring its IP on another domain to use a CNAME record, and not the IP in an A record, as the load balancer IP is subject to change.

Results from my first high-load scalable system
Putting the cloud on a scale so it’s not so heavy

I’ve wanted to create and test a large-scale application for a very long time but have never really had the chance until recently. The Vintage Experience project I did earlier this year finally gave me the opportunity. As one of many parts of the project, I was tasked to create a voting system that could handle 1 million votes via a web page in a 30 second time span. The final system was deployed successfully without any problems for Gala Artis 2013 (a French Canadian artist/TV awards show). The following are the results of my implementation and testing.

The main front-end was done via a static HTML page (smart-phone optimized) that was hosted by Amazon S3, where handling 33k requests/second is a drop in the bucket. All voting requests were done via AJAX from this web page to backend servers hosted by Amazon EC2.

The backend was programmed in GoLang as a simple web server, optimized for memory and speed, which spawned a new goroutine for each incoming request. The request returned a message to the user stating either the error message, or success if the vote was added to the database. Each server held a single persistent MySQL connection to an Amazon RDS “Large DB Instance” with the minimum IOPS (1000). Votes from a server were sent to the database in batches once a second, or earlier if 10,000 votes had been received.

The servers were Amazon “M1 Standard Extra Large” (m1.xlarge) instances running Linux, of which there were 6 total, handling vote requests delegated by a round-robin DNS on Amazon’s Route 53. During stress testing, each server was found to be able to handle 6800 requests/second, and load was staying under 3, so there were was probably another bottle neck. Running the same tests using php(sapi)+apache(fork), only 4500 requests/second could be executed, and there was a 16+ load.

On the servers, I found it necessary to set the following sysctl setting to increase performance “net.core.somaxconn=1024”. The following commands need to be run to execute this:

sysctl 'net.core.somaxconn=1024' #Store for the current computer session
echo 'net.core.somaxconn=1024' >> /etc/sysctl.conf #Set after a reboot

Stress test client instances were also run on Amazon as m1.xlarge instances, and were found to be able to push 5000-6000 requests/second. The GoLang test clients spawned 200 requests at a time and waited for them to finish before sending the next batch. The client system needed the following sysctl settings for optimal performance:

net.ipv4.tcp_tw_recycle=1
net.ipv4.tcp_tw_reuse=1
net.ipv4.tcp_fin_timeout=30
net.ipv4.ip_local_port_range="15000 65534"