Cloud Computing

CLOUD COMPUTING

Hello , here is an interesting and very very useful post . I am sure you would have heard the word cloud computing at least a dozen of times. 

Are you confused about the cloud computing world?

well then this post is for you . 

The first and obvious question you would get is what is cloud computing ?

Everything is going to be cloud in a couple of years - In simple words cloud computing is just performing computations in the cloud .

Now worried about the words computations and cloud?

Relax , Cloud is just a cluster of computers.

Cluster is  a group of computers connected to one another to perform some operation as shown in the figure below.

 Computing can be anything ,

starting from 1+1=2 to estimating the stock market .

starting from storing your pocket money expense sheet to storing the user profile of 1 billion users.

starting from setting up a LAN for you to chat with your friend to setting up a WAN with a 100 million users

Yes you are reading it right .....and the power of computations in cloud goes on and on ......

Want to know more about it?? Carry on reading , you will end up with interesting facts about the cloud computing world .

Next , you need to understand the 3 main categories of services in the cloud .

1 } Software as a service (SaaS)

2 } Platfrom as a service (PaaS)

3 } Infrastructure as a service (IaaS)

 SaaS is a software delivery method that provides access to software and its functions remotely as a Web-based service. SaaS allows organizations to access their business functionality at a cost which is  less than the cost required for licensed applications.

Advantages of SaaS

Since the software is hosted on remotely , there is no need for additional hardware hence the cost reduces .

The organizations need not perform the installation or set up and maintenance . The cloud providers will do everything on behalf of their clients . etc

Examples

Amazon Rackspace .

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 PaaS is a way to rent hardware, operating systems, storage and network capacity over the Internet. This service allows the customer to rent virtualized servers and services for running existing applications or developing and testing new ones.

Advantages of PaaS

This service eliminates the need for purchasing any storage devices and operating systems and other devices required for the network setup .

The client can make use of all the resources of the cloud just by having an internet connection to access the cloud provider's services.

Examples

MS Azure .

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IaaS is a  model in which an organization outsources the equipment used to support operations, including storage, hardware, servers and networking components. The service provider owns the equipment and is responsible for housing, running and maintaining it. The client typically pays on a per-use basis.

Advantages of IaaS

The user is free from owning and maintaining the storage and hardware and servers .

Examples

Google Apps .

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Please feel free to leave your comments or doubts

thank you :)

client and server interaction

Hi, welcome,

Ever wondered how does your server identify you and provide the service you request for? 

             Its very simple. In this post you will learn about a simple interaction between the client and the server.

To start off,  lets look at one of the simplest things that you can do - we will initialize a stream connection and receive a message from a remote server.

Consider the below c program - a simple code for the client .

Here socket connection is established between the client and the server and the client receives the message sent by the server, note that for demonstration purpose we use the same system as the client and the server .

Well lets start coding the client machine

Here it goes !!!

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>

 #define MAX_SIZE_OF_MESSAGE 500
#define PORT_NUMBER 2343

int main(int argc, char *argv[])
{

     1 } char buffer[MAX_SIZE_OF_MESSAGE + 1];

     2 } int len, wetechies_socket;

     3 } struct sockaddr_in destination_machine;

     4 } mysocket = socket(AF_INET, SOCK_STREAM, 0);

     5 } memset(&dest, 0, sizeof(dest));      

         

     6 } dest.sin_family = AF_INET;

     7 } destination_machine.sin_addr.s_addr = inet_addr("127.0.0.1"); 

     8 }  dest.sin_port = htons(PORTNUM);         

       

     9 } connect(wetechies_socket, (struct sockaddr *)&destination_machine, sizeof(struct sockaddr));

   10 }  len = recv(wetechies_socket, buffer, MAX_SIZE_OF_MESSAGE, 0);

   11 }   buffer[len] = '\0';

   12 } printf("Received %s (%d bytes).\n", buffer, len);

   13 }  close(wetechies_socket);

   14 } return EXIT_SUCCESS;

}

***********************************************************************************************

Explanation for the client program

Line 1 - An array by name buffer of type char is created with the size MAX_SIZE_OF_MESSAGE + 1 (+1 is used so that we can add the null terminator too).

Line 2 - Initialization of the variables len  (used to hold the length of the message received from the server (line 10) ) and mysocket .

Line 3 - Creates a variable destination_machine which is a struct of type sockaddr_in , This struct stores information about the machine we want to connect to.

Line 4 - The socket() function tells our OS that we want a file descriptor for a socket which we can use for a network stream connection; what the parameters mean is mostly irrelevant for now. But if your are interested you can always explore it by using the man page by hyst typing the command man socket.

Line 5 - memset() is used to zero the struct variables. you can again use the man page by typing the command man memset to know more about the memset function

Line 6 - Sets the address family. This should be the same value that was passed as the first parameter to socket(); for most purposes AF_INET will serve.

Line 7 - Here is where we set the IP address of the machine we need to connect to(here we use 127.0.0.1 which is know as the loopback address and refers to your own machine). The variable destination_machine.sin_addr.s_addr is just an integer stored in Big Endian format, but we don't have to know that as the inet_addr() function will do the conversion from string into Big Endian integer for us. 

Line 8 - This line sets the destination port number. The htons() function converts the port number into a Big Endian short integer. If your program is going to be run solely on machines which use Big Endian numbers as default then destination_machine.sin_port = 21 would work just as well. However, for portability reasons htons() should always be used. 

Line 9 - Establishes a connection with the server machine.

Line 10 - Receives up to MAX_SIZE_OF_MESSAGE bytes of data from the connection and stores them in the buffer string. The number of characters received is returned by recv()

Line 11 - The data received will not automatically be null terminated when stored in the buffer, so we need to do it ourselves with buffer[inputlen] = '\0'. 

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Now lets start coding the server machine

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <unistd.h>

#include <arpa/inet.h>

#include <sys/types.h>

#include <netinet/in.h>

#include <sys/socket.h>

#define PORTNUM 2343

int main(int argc, char *argv[])

{

    char msg[] = "wetechies !\n";

    struct sockaddr_in destination_machine;

    struct sockaddr_in server;

    int wetechies_socket;          

    socklen_t socksize = sizeof(struct sockaddr_in);

    memset(&server, 0, sizeof(server));        

    server.sin_family = AF_INET;              

    server.sin_addr.s_addr = htonl(INADDR_ANY);

    server.sin_port = htons(PORTNUM);          

    wetechies_socket = socket(AF_INET, SOCK_STREAM, 0);

    bind(wetechies_socket, (struct sockaddr *)&server, sizeof(struct sockaddr));

    listen(wetechies_socket, 1);

    int connection_socket = accept(wetechies_socket, (struct sockaddr *)&destination_machine, &socksize);

    while(connection_socket)

    {

        printf("Incoming connection from %s - sending welcome\n", inet_ntoa(destination_machine.sin_addr));

        send(connection_socket, msg, strlen(msg), 0);

       connection_socket = accept(wetechies_socket, (struct sockaddr *)&destination_machine, &socksize);

    }

    close(connection_socket);

    close(wetechies_socket);

    return EXIT_SUCCESS;

}

***********************************************************************************************

Explanation for the server program

In fact, this is very similar to the client program. The main difference is that rather than creating a sockaddr_in with information about the machine we are trying to connect, we create it with information about the server, and then we bind() it to the socket. 

The listen() function then tells our program to start listening using the given socket.

The second parameter of listen() allows us to specify the maximum number of connections that can be queued.

Each time a connection is made to the server it is added to the queue.We take connections from the queue using the accept() function. The accept() function returns another socket. This socket is essentially a "session" socket, and can be used solely for communicating with connection we took off the queue. The original socket (mysocket) continues to listen on the specified port for further connections.

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Leave your doubts or suggestions in comments section...

Installing tomcat in linux

Welcome Folks.. This post will guide you in the installation and configuration of the apache tomcat server

In order to work with the tomcat server, you need to have the Java environment set, if you haven't done it yet then follow this post

Installation and configuration of the apache tomcat server

Steps to download and install the tomcat server

Step 1 : Download the tomcat sever from http://tomcat.apache.org/ .

             Once downloaded, you should have a folder named 

                                           apache-tomcat-6.0.29.tar.gz (similar to this).

Step 2 : Extract the folder you just downloaded by using the below command

                                          

                                           tar -xvfz apache-tomcat-6.0.29.tar.gz

Step 3 :  Now the next step is to set up the paths for catalina as below

export CATALINA_HOME=/location where you have extracted the tomcat

 ex : export CATALINA_HOME = /home/vignesh/Desktop/apache-tomcat-7.0.37

 Add the following lines to your /etc/profile file so that it can set the CATALINA_HOME variable automatically when the system restarts.

 

Step 4 : Run the following command to start the Tomcat server: 
      
                        $CATALINA_HOME/bin/startup.sh 

Step 5 : Verify that the Tomcat server is running by browsing to

                        http://Your_IP_Here:8080/

        ex : http://localhost:8080 on doing this, you should see something like below

Congratulations you have now installed the TOMCAT SERVER successfully !!!

let us have a check by running a simple program

1. Type the below given program in the text file

                         <HTML>
                                <BODY>
                                        Hello Developer !!!
                                </BODY>
                         </HTML>

2. Save the file with .jsp extension in the below path where all your .class and .jsp files should be  
    present

                           /apache-tomcat-7.0.37/webapps/ROOT/

3. In order to execute the program, you need to start your tomcat server, its so simple 

- open your terminal and traverse to the bin folder in tomcat which you had downloaded by 

following this post

- type ./catalina.sh start and ./catalina.sh stop to stop the server

Example:root@localhost:/home/vignesh/Desktop/apache-tomcat-7.0.37/bin# ./catalina.sh start

Note: Once you have started the catalina server, you can verify it by typing  

http://localhost:8080 on the address bar of your browser.Tats it !!!!! 

4 . Now from the browser open the file you just created . 

    Example : http://localhost/apachetesting.jsp

    You should see the text Hello Developer on your browser.

Leave your doubts or suggestions in comments section..