Architecting your application for the cloud

Recently I have given a speech on 'Architecting your application for the cloud' on Basis Softexpo 2012. I have uploaded my slides on slideshare. You can get the slides from here.
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Logrotate for virtual hosts

First create a file named 'virtualhosts' under /etc/logrotate.d/ folder. Then we set the path of the log files for our virtual hosts into the file. Suppose we have two virtual hosts for domain1.com and domain2.com. Then our file will be as the below:

/path_to_domain1.com_log/*log /path_to_domain2com_log/*log {
        rotate 14
        daily
        compress
        delaycompress
        sharedscripts
        postrotate
                /usr/sbin/apache2ctl graceful > /dev/null
        endscript
}

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minimize attack with iptables

You can minimized DDOS attack with some basic actions with the iptables.
Syn-flood protection:

In this attack system is floods with a series of SYN packets. Each packets causes system to issue a SYN-ACK responses. Then system waits for ACK that follows the SYN+ACK (3 way handshake). Since attack never sends back ACK again entire system resources get fulled aka backlog queue. Once the queue is full system will ignored incoming request from legitimate users for services (http/mail etc). Hence it is necessary to stop this attack with iptables.

Force SYN packets check:
Make sure NEW incoming tcp connections are SYN packets; otherwise we need to drop them:

iptables -A INPUT -p tcp ! --syn -m state --state NEW -j DROP

Force Fragments packets check
Packets with incoming fragments drop them. This attack result into Linux server panic such data loss.

iptables -A INPUT -f -j DROP

XMAS packets
Incoming malformed XMAS packets drop them:

iptables -A INPUT -p tcp --tcp-flags ALL ALL -j DROP

Drop all NULL packets
Incoming malformed NULL packets:

iptables -A INPIT -p tcp --tcp-flags ALL NONE -j DROP

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How to prevent DDOS attack

Different people are sitting there in the world to make DDOS attacks. This kind of attack main done by web hosting company to crush other hosting servers. You can prevent DDOS attack with the following steps:

• 1. use iptables
• 2. Use log rotator
• see access log and block the attacker's IP address,

Let me know what I missed... :)
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How to block an IP address

You can block a malicious IP address with the iptables. you can stop all incoming request from that specific address with the following command:

sudo /sbin/iptables -I INPUT -s 173.242.125.206 -j DROP

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How to configure logrotate

you can find the main logrotate configuration file in

/etc/logrotate.conf

This shows the default rules for log rotation. we will get the application specific configuration on

ls /etc/logrotate.d

Set the rotation count with

rotate 4

So, we will get four log file. We can specify the interval also with

weekly
daily
monthly
yearly

We limit the log file size with

size 100k
size 100M
size 100G

Here we limit the size to 100 kilobytes or 100 megabytes or 100 gigabytes, use the one that you needs. We compress our log file

compress
delaycompress
nocompress

with delaycomress we delay the compresssion. delaycomress only works if you define compress. You can directly apply the changes with the below command:

/usr/sbin/logrotate /etc/logrotate.conf

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how to empty a file in linux

You can empty a file using the following command without deleting it in unix environment:

cat /dev/null > largefile

it's empty now. :)
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Joomla! Mobile Development Beginner’s Guide is out now

Hey everyone, want to develop websites for mobile devices with Joomla, 'Joomla! Mobile Development Beginner’s Guide' is out there. go get your copy and start developing. In the coming days, I will also discuss about different feature of the book. Thanks. You can order from here.
See the book OpenCart 1.4 Template Design Cookbook.
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How to create a git repository

To create a git repository, create a folder of the project name, like 'test'.

mkdir test

Then go into the folder with:

cd test

And run the below command

git --bare init

Now, go to your local machine, and run the below commands:

mkdir project
cd project
git init

And create your project files here.

git add .
git commit -am 'message'
git remote add origin ssh:user@ipaddress:/path_to_project
git push origin master

Then you can make a clone of your repository on your server machine now:

git clone user@ipaddress:/path_to_project

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Create init page for nginx

In this article, we will create an init page for nginx server. Open the file with nano.

sudo nano /etc/init.d/nginx

Then write the following code in the bash file:

#! /bin/sh

PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
DAEMON=/usr/local/sbin/nginx
NAME=nginx
DESC=nginx

test -x $DAEMON || exit 0

# Include nginx defaults if available
if [ -f /etc/default/nginx ] ; then
        . /etc/default/nginx
fi

set -e

case "$1" in
  start)
        echo -n "Starting $DESC: "
        start-stop-daemon --start --quiet --pidfile /usr/local/nginx/logs/$NAME.pid \
                --exec $DAEMON -- $DAEMON_OPTS
        echo "$NAME."
        ;;
  stop)
        echo -n "Stopping $DESC: "
        start-stop-daemon --stop --quiet --pidfile /usr/local/nginx/logs/$NAME.pid \
                --exec $DAEMON
        echo "$NAME."
        ;;

  restart|force-reload)
        echo -n "Restarting $DESC: "
        start-stop-daemon --stop --quiet --pidfile \
                /usr/local/nginx/logs/$NAME.pid --exec $DAEMON
        sleep 1
        start-stop-daemon --start --quiet --pidfile \
                /usr/local/nginx/logs/$NAME.pid --exec $DAEMON -- $DAEMON_OPTS
        echo "$NAME."
        ;;
  reload)
      echo -n "Reloading $DESC configuration: "
      start-stop-daemon --stop --signal HUP --quiet --pidfile /usr/local/nginx/logs/$NAME.pid \
          --exec $DAEMON
      echo "$NAME."
      ;;
  *)
        N=/etc/init.d/$NAME
        echo "Usage: $N {start|stop|restart|reload|force-reload}" >&2
        exit 1
        ;;
esac

exit 0

We change the permission on the file.

sudo chmod +x /etc/init.d/nginx

And then added it to run on the boot time of the server.

sudo /usr/sbin/update-rc.d -f nginx defaults

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bind() to 0.0.0.0:80 failed (98: Address already in use)

I have installed nginx server on ubuntu 11.04(Natty Narwhal). After installation while I start the nginx server, I got the error:

bind() to 0.0.0.0:80 failed (98: Address already in use)

I found the apache server is running on the same port on 80. So, I stop the Apache server and The error gone.
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jQuery Mobile jumpy and blinky issue

I have used jQuery mobile and implemented transition effect into my site. Then some pages jump to previous and next page. This issue is known as 'Jumpy and blink issue'. I have removed the the page transition effect and set the following:

defaultPageTransition: none.

Then the problem solved. :)
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svn: Error converting entry in directory '/' to UTF-8

I have got an error describing that some filenames can't be converted to UTF-8 format while committing to svn. Later I found that there was some space in the filename like 'tahsin hasan'. It's a valid name in windows, but it's not a valid in unix environment. I have changed the names, then the error was resolved.
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