Understanding Azure Services

Understanding how virtual machine works in azure:

It offers us Infrastructure as a service(IaaS) i.e. using this service we can create a virtual machine on demand either from standard images or from one we supply

Structure:

• ​ VHDs that back azure virtual machine are stored in azure storage blobs,this provide redundancy which ensures that even in case of hardware or disk failures VMs keep on working
• Azure offers gallery of VHDs (also called images) , we can choose a VHD from gallery of stock VHDs or we can upload our own custom VHD
• We can also copy a VHD out of azure and then run it locally 

Scenario's to use VM:

• ​ Creating a Dev/Test environment 
• Moving application(with less dependency on local system) from local datacenter to azure
• Extending our local data center with azure virtual machine by using azure virtual network

Understanding how websites work in azure

Scenarios to use websites:​

• We prefer using azure websites in place of hosting website on VM or using a cloud service when we just want to handle the website related tasks and leave the  task related to administrating of website upto azure 
• For development websites supports .net,php,nodejs,java , python along with SQL database and mysql database.

Understanding  azure cloud services:

• ​This service is mostly used in cases when we want to build scalable, reliable and low admin apps. This is also referred to as platform as a service.
• When running a cloud service , the code of our application (built in c#, java, php , nodejs or something else)runs on a virtual machine(instances) running a version of windows server.
• This virtual machine is managed by azure itself and because of this reason our application should not maintain state in the web or worker role instance instead it should use azure data management services for this purpose.
• When creating a cloud service we have two roles to choose from both of which are hosted on windows server : Web role and worker role. 
• The main difference between the two is that instance of web role runs IIS while instance of worker role do not.
• In order to scale an application up or down we can request azure to create more instances of either role or shut down an existing instance.  
• Like in case of VM the charges are only made in case when the web/worker role is running.
• This service should be preferred in case when we need more control over the platform than azure websites provide but less control over the operating system.

*The computer role instances in windows azure are stateless.To upgrade hardware because of a fault or any other reasons a computer role instance might stop on one physical server and another will pick it up.This is done through fabric controller whose task is to check the status of the hardware and software of the machine instances.In case of failure, it enforces SLAs by automatically relocating the VM instances.

Understanding data management in azure:
​
Azure provides many different ways to store data , with any of the options provided by azure 3 copies of the data is kept across a datacenter and 6 copies in case we kept our data geo redundant. 

In virtual machine:
​ We can run relational systems as well NoSql technologies in VM created using Azure Virtual machines , however if we use this technique we need to handle the administration for that database system as well, in the following other cases azure does this work for its users.

Azure Sql database:

​Azure SQL Database provides all of the key features of a relational database management system, including atomic transactions, concurrent data access by multiple users with data integrity, ANSI SQL queries, and a familiar programming model. Like SQL Server, SQL Database can be accessed using Entity Framework, ADO.NET, JDBC, and other familiar data access technologies.


Tables:

This follows a NoSql approach and provides a key value based storage
Azure Tables let an application store properties of various types, such as strings, integers, and dates. An application can then retrieve a group of properties by providing a unique key for that group
​It is also referred to as azure storage, storage tables or azure storage.
Tables are usually less expensive to use than SQL Database's relational storage.
Tables are best to use in case when we need fast access to typed data and do not require  to perform any complex sql queries on this data.

Blobs:

​These are used to store unstructured binary data
Inexpensive and a single blob can store upto 1 TB of data.
They are useful when application wants to store video, massive files and other binary information.

Azure file services:

​This service allows us  to use Server message block protocol to share files between VMs.
 In addition, the files can also be accessed at the same time via a REST interface, which allows us to access the shares from on-premises when we also set up a virtual network.

Understanding Azure marketplace:
 ​Azure Marketplace lets us find and buy Azure applications and commercial datasets and use them as part of your Azure applications.Potential customers can search to find Azure applications that meet their needs. Customers can search for commercial datasets as well, including demographic data, financial data, geographic data, and more. When they find something they like, they can access it either from the vendor, directly through the Marketplace or Store web locations or in some cases from the Management Portal.



References:
(i) http://azure.microsoft.com/en-in/documentation/articles/fundamentals-introduction-to-azure/