Creating New users in postgresql and providing grants to the users

Steps to create read only user in postgre DB

1. Command to create the user

create user USER_NAME password 'PASWWORD';

2. Set read only to the user

alter user USER_NAME set default_transaction_read_only = on;

3. Provide DB previlages to user

GRANT select on DB_NAME to USER; // if only db name doesn't work. give list of tables in command, so that the user can have permission to all the tables

4. login to DB

 psaql -h HOSTNAME -UUSERNAME -d DBNAME

5. Once you logged into the DB. execute below commands

GRANT CONNECT ON DATABASE db_name to user_name;
GRANT USAGE ON SCHEMA public to user_name;
GRANT SELECT ON ALL SEQUENCES IN SCHEMA public TO user_name;
GRANT SELECT ON ALL TABLES IN SCHEMA public TO user_name;

Creating SSL Certificate in Ubuntu

What is SSL certificates,How HTTPS works,How to generate CSR and eventually installing an SSL certificate . The Secure Socket Layer was created by netscape to ensure secure transactions between web servers and browsers,mail servers and mail client 

HTTPS or Hypertext Transfer Protocol Secure indicates that the website has been authenticated by a third party Certification Authority (CA).HTTPS is a visual indication that information is being exchanged for the session in a more secure way.HTTPS appears in the URL when a website is secured by an SSL certificate.The details of the certificate, including the issuing authority and the corporate name of the website owner, can be viewed by clicking on either the lock symbol on the browser bar.

How SSL Works

1. A browser attempts to connect to a website secured with SSL.
2. The browser requests that the web server identify itself.
3. The server sends the browser a copy of its SSL Certificate.
4. The browser checks whether it trusts the SSL Certificate. If so, it sends a message to the server.
5. The server sends back a digitally signed acknowledgement to start an SSL encrypted session.
6. Encrypted data is shared between the browser.

Why do we need SSL

If you are transmitting sensitive information on a web site, such as credit card numbers or personal information, you need to secure it with SSL encryption.With booming Internet trends and fraud, most will not submit their private details on the web unless they know that the information they provide is securely transmitted and not accessible for anyone to view.

Self Signed and Signed SSL Certificates

Whether you get your certificate signed by a certificate authority or sign it yourself, there is one thing that is exactly the same on both.The data sent over an https connection will be encrypted regardless of whether the certificate is signed or self-signed.In other words, both types of certificates will encrypt the data to create a secure website.A certificate authority tells your customers that this server information has been verified by a trusted source.he problem with using a self-signed certificate is that nearly every Web browser checks that an https connection is signed by a recognized CA. If the connection is self-signed, this will be flagged as potentially risky and error messages will pop up encouraging your customers to not trust the site.Since they provide the same protection, you can use a self-signed cerificate anywhere you would use a signed certificate.Self-signed certificates are great for testing servers.If you're creating a website that you need to test over an https connection, you don't have to pay for a signed certificate for that testing site.If You're Doing Ecommerce You Need a Signed Certificate.

What is Certificate Authority 

A certificate authority is an entity which issues digital certificates to organizations or people after validating them.Certification authorities have to keep detailed records of what has been issued and the information used to issue it, and are audited regularly to make sure that they are following defined procedures.For example Versign,GoDaddy,GlobalSign.

Process involved in buying SSL certificate

1. Generate a Certificate Signing Request (CSR) for the web server you plan to secure 
2. Contact any of CA(Versign,GoDaddy,GlobalSign,Thawte)
3. Choose your Type of SSL Certificate and Buy
4. Apply the certificates on your web server. 

Generate a CSR with OpenSSL

To install a digital certificate, you must first generate and submit a Certificate Signing Request (CSR) to the Certification Authority (CA).The CSR contains your certificate-application information.

Install Open-SSL on your server,this is a common package and will be available on all of the major distros through their package installer.

Step 1: Generate Private key : 

openssl genrsa -des3 -out server.key 2048

Generating RSA private key, 2048 bit long modulus
.+++
........................+++
e is 65537 (0x10001)
Enter pass phrase for server.key:abcde
Verifying - Enter pass phrase for server.key:abcde

Step 2: Generate a CSR : openssl req -new -key server.key -out server.csr

Enter pass phrase for server.key:xyz
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [XX]:abc
State or Province Name (full name) []:abc
Locality Name (eg, city) [Default City]:abc
Organization Name (eg, company) [Default Company Ltd]:abc
Organizational Unit Name (eg, section) []:abc
Common Name (eg, your name or your server's hostname) []:*.abc.com or abc.com [actual domain name for that you need to buy ssl]
Email Address []:abc@xyz.com

Please enter the following 'extra' attributes
to be sent with your certificate request

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:password
An optional company name []:abc org


After the verification of SSL from Service Provider, download the certificate and intermediate certificate.


Now you can upload this ssl and server.key file to ELB to enable SSL.

While uploading if you face any error like  "Invalid Private Key", than convert the private key file to equivalent .pem file 


openssl rsa -in server.key -outform PEM -out server.key.pem

Than try again.

Installing GIT on your local ubuntu machine and some basic commands

Step 1: sudo apt-get install git-core //Installs git tool in your local ubuntu machine.

Step 2: //Checking GIT version

git --version
---> git version 1.9.1


Step 3: Setting User Name and EMail Id:

  git config --global user.name "Aditya Hegde"
  git config --global user.email "abc@gmail.com"


List of other git commands:
1.  AVOID MERGE COMMITS FOR PULLING
// You pull latest changes from a remote repository and if these changes are divergent then, by default Git creates merge commits. We can avoid this via following settings.

* git config --global branch.autosetuprebase always


2. COLOR HIGHLIGHTING
  // The following commands enable color highlighting for Git in the console.
  * git config --global color.ui true
  * git config --global color.status auto
  * git config --global color.branch auto

3. SETTING DEFAULT EDITOR
// By default Git uses the system default editor which is taken from the VISUAL or EDITOR environment variable. We can configure a different one by using git config.
  * git config --global core.editor vim

4. SETTING DEFAULT MERGE TOOL
// Git does not provide a default merge tool for integrating conflicting changes into your working tree. We can set default merge tool by enabling following settings.
  * git config --global merge.tool vimdiff

5. LISTING GIT SETTINGS
// To verify your Git settings of the local repository use git config –list command as given below.
  * git config --list


Creating Operation:

A. Creating New Group and User
1. Creating a Group:
   * groupaddgroup-name

2. Adding new user to group
   * useradd -G group-name -d /home/gituser -m -s /bin/bash username

3. Changing the password for user:
   * passwd user-name
  // This will prompt for new password

B. Creating Bare Repository:
1.  Create a directory with .git extension
    * mkdir directory_name.git

2. Switch to newly created directory.
   * cd directory_name.git

3. // Initializing new empty repository with --bare option
  *  git --bare init
-----> Initialized empty Git repository in /home/gituser/project.git/

Installing S3CMD tool in your local ubuntu or Amazon Linux Machine

S3CMD tool is used to operate with AWS S3 Bucket. Below are the steps to install s3cmd tool in your local machine.


Step 1: Download the s3cmd tool package.

wget http://sourceforge.net/projects/s3tools/files/s3cmd/1.5.0-alpha3/s3cmd-1.5.0-alpha3.tar.gz

Step 2: unzip the downloaded package.
tar xzf s3cmd-1.5.0-alpha3.tar.gz

Step 3: Switch to setup folder.
cd  s3cmd-1.5.0-alpha3/setup

Step 4: Execute the setup.py file.
python setup.py install  // This will install s3cmd tool on your machine.


Step 5: Configuring with one of the s3 bucket.

s3cmd --configure
// This will prompt for Access Key and Secret Key of the bucket. 

Creating new User in Amazon EC2

Step 1: Login to EC2 instance using SSH and public key

Step 2:add a new user
   sudo adduser newuser[newuser name]

Step 3: Switch to the new user
   sudo su - newuser[newuser name] -- connect to new user a/c

Step 4: Create a .ssh directory for the authorized_keys file.
   mkdir .ssh

Step 5: change the permission of .ssh
   chmod 700 .ssh

Step 6: Create a file named "authorized_keys" in the .ssh directory.
   touch .ssh/authorized_keys
   //or we can user vi editor

Step 7: Change the file permissions of the authorized_keys file to 600 (this means only the file owner can read or write to the file).
   chmod 600 .ssh/authorized_keys  //this step is very important

Step 8: use ssh-keygen to get the public key for your key pair
   ssh-keygen -f username  // This command will create 2 files one with .pub extension.

Step 9: Copy the content generated of key.pub to .ssh/authorized_keys and chanage permission of authorized_keys to 600
//careful while copying the contents.

Step 10: Copy the content of another public file to file.pem in your local machine.
    //that creates your public ssh key. i.e .pem file.

Step 11: Now you have added a new user to the aws ec2-machine through command and try to connect to the ec2 machine with the new user name and new .pem key.


Note: Do not perform these actions as a root user.


Providing root user / admin user access to newly added user

sudo adduser <username> sudo #for sudo user
sudo adduser <username> admin #for admin user

What Is Cloud Computing?

What is the cloud? Where is the cloud? Are we in the cloud now? These are all questions you've probably heard or even asked yourself. The term "cloud computing" is everywhere.
In the simplest terms, cloud computing means storing and accessing data and programs over the Internet instead of your computer's hard drive. The cloud is just a metaphor for the Internet. It goes back to the days of flowcharts and presentations that would represent the gigantic server-farm infrastructure of the Internet as nothing but a puffy, white cumulonimbus cloud, accepting connections and doling out information as it floats.
What cloud computing is not about is your hard drive. When you store data on or run programs from the hard drive, that's called local storage and computing. Everything you need is physically close to you, which means accessing your data is fast and easy, for that one computer, or others on the local network. Working off your hard drive is how the computer industry functioned for decades; some would argue it's still superior to cloud computing, for reasons I'll explain shortly.
The cloud is also not about having a dedicated network attached storage (NAS) hardware or server in residence. Storing data on a home or office network does not count as utilizing the cloud. (However, some NAS will let you remotely access things over the Internet, and there's at least one NAS named "My Cloud," just to keep things confusing.)
For it to be considered "cloud computing," you need to access your data or your programs over the Internet, or at the very least, have that data synchronized with other information over the Web. In a big business, you may know all there is to know about what's on the other side of the connection; as an individual user, you may never have any idea what kind of massive data-processing is happening on the other end. The end result is the same: with an online connection, cloud computing can be done anywhere, anytime.

Consumer vs. Business
Let's be clear here. We're talking about cloud computing as it impacts individual consumers—those of us who sit back at home or in small-to-medium offices and use the Internet on a regular basis.
There is an entirely different "cloud" when it comes to business. Some businesses choose to implement Software-as-a-Service (SaaS), where the business subscribes to an application it accesses over the Internet. (Think Salesforce.com.) There's also Platform-as-a-Service (PaaS), where a business can create its own custom applications for use by all in the company. And don't forget the mighty Infrastructure-as-a-Service (IaaS), where players like Amazon, Microsoft, Google, and Rackspace provide a backbone that can be "rented out" by other companies. (For example, Netflix provides services to you because it's a customer of the cloud-services at Amazon.)

Of course, cloud computing is big business: The market was already generating $100 billion a year in 2012. It could be $270 billion by the year 2020.