We live in dynamic times. Buzzwords such as cloud computing, elastic scale, reliability and their synonyms are taking more and more space in our daily life. People (developers) want to move to the cloud. They are often confused by all the new terms. In this part 1 of [we-will-see-at-the-end-how-many] articles I will try to explain with non-geeky words the Windows Azure terms.
First of all, what is Cloud Computing before all? This is when Computing power (namely CPU, RAM, Storage, Networking) is delivered as a service via a network (usually internet), and not as a product (a server that we buy).
Cloud computing is a marketing term for technologies that provide computation, software, data access, and storage services that do not require end-user knowledge of the physical location and configuration of the system that delivers the services. A parallel to this concept can be drawn with the electricity grid, wherein end-users consume power without needing to understand the component devices or infrastructure required to provide the service.
So what is Windows Azure? Is it the new server operating system from Microsoft? Is it the new hosting solution? Is it the new workstation OS? Well, Windows Azure is the Microsoft’s Cloud Computing platform. It delivers various cloud services. Compute, Database, Storage, CDN, Caching, Access Control to name few.
Next part of the article will be focusing on Windows Azure Compute services.
Windows Azure Guest OS? When we talk about cloud computing, inevitably we talk about virtualization. Virtualization at very big degree. And when we talk about virtualization, we have a Host OS and Guest OS. When we talk about Windows Azure OS, we talk about Windows Azure Guest OS. This is the operating system that is installed on the Virtual Machines that run in the cloud. Windows Azure Guest OS has 2 families – OS Family 1 and OS Family 2. Windows Azure Guest OS Family 1 is based on Windows Server 2008 SP 1 x64, and Family 2 is based on Windows Server 2008 R2. All and any guest OS is 64 bits. You can get the full list of Windows Azure Guest OS here.
Windows Azure Cloud Service, or Hosted Service. The Hosted Service is the essence of your Cloud application:
A hosted service in Windows Azure consists of an application that is designed to run in the hosted service and XML configuration files that define how the hosted service should run
A hosted service can have one or more Roles.
Now it comes to the Roles. Our cloud application can be a Web Based application, or a background processing application, or some legacy application which is hard to migrate. Or mix of the three. In order to make things easy for developers, Microsoft has defined 3 distinguished types of “Roles” – Web Role, Worker Role and VM Role. You can read a bit more for the “Role”s here. But the main idea is that a Role defines an application living environment. The Role contains all the code that our application consists of. It defines the environment where our application will live – how many CPUs will be installed; the amount of RAM installed; volume of local storages; will it be a full IIS or a background worker; will it be Windows Azure Guest OS 1.x or 2.x; will it has open ports for communication with outer world (i.e. tcp port 80 for Web Role); will it has some internal TCP ports open for internal communication between roles; what certificates will the environment has; environment variables; etc.
The Role is like a template for our cloud application. When we configure our Cloud Service (or Azure Hosted Service), we set the number of instances involved for each Role.
Instance is a single Virtual Machine (VM), which has all the properties defined by the Role and has our application code deployed. When I mentioned that the Role defines the number of CPUs, RAM, local storage, I was referring the configuration for each VM where our code will be deployed. There are couple (5) of predefined VM configuration which we can use:
|Virtual Machine Size||CPU Cores||Memory||Cost Per Hour|
|Extra Small||Shared||768 MB||$0.04|
|Extra Large||8||14 GB||$0.96|
More information on Virtual Machine sizes can be found here.
And here comes the beauty of the Cloud. We code once. We set the overall parameters once. And we deploy once! If it comes that we need more servers – we just set the number of instances for our role. We do it live. There is no downtime. Windows Azure automatically will launch as many VMs as we requested. Will configure them for our application and will deploy our code in each and every one of them and will finally join them to the cluster of our highly available and reliable cloud application. When we don’t need (let’s say) 10 servers anymore, then we can easily instruct Windows Azure that we only need 2 from now on and that’s it. The cloud will automatically shutdown 8 servers and remove them, so we won’t be paying any more extra money.
It is important to note, though, that the Role defines the size of the VM for all the Instances of it. We cannot have instances of same Role but different VM size. This is by design. If we defined our Role to use Extra Large VM, then all the instances we have will be running on that size of VM.
I hope that this article helped you understand couple of basic terms about Windows Azure. You shall be able to confidently answer the following questions:
- What is Windows Azure ?
- What is Windows Azure Hosted Service (or just Hosted Service)?
- What is a Role?
- What is a Role Instance (or just Instance)?