Cloud Terminology

This is the second of a series of blog posts around Cloud Computing. It gives an overview about the current Cloud Computing trends and explains how to set up a private cloud environment with Microsoft's System Center products.

This post explains the key criteria, different approaches and service models of cloud computing.

Cloud Computing Key Criteria

• Elasticity and Flexibility
  The needed resources like CPU, Memory and Storage can be dynamically allocated. It is possible to quickly scale vertically and horizontally.
• Self-Service
  The cloud is exposed to the end-user in a way that they can easily control their needed systems and resources. There is no human-interaction needed for creating new virtual machines, deploying applications or scaling them.
  
• Completely Automated
  The most important criteria of cloud computing is the automation of the complete infrastructure. Systems and Applications are provided in an automated way where no human-interaction is needed.
  

Cloud Service Models

• Infrastructure as a Service (IaaS)
  This service model gives the user the possibility to provision virtual machines on operation system level. It is possible to deploy and run arbitrary software. The customer does not have any control of the underlying cloud infrastructure. But she can manage operating systems, storage and network components like firewalls and load balancers.
• Platform as a Service (PaaS)
  The customer can deploy applications on PaaS cloud solutions without having access to the underlying infrastructure like operating system, network or servers. The applications are restricted to the supported programming languages and technologies. PaaS solutions provide automated deployment processes, monitoring and easy horizontal scaling features (spreading multiple servers).
  
• Software as a Service (SaaS)
  This model allows the customer to use applications hosted externally, like Office and Web Storage solutions. The customer does not have any access to the cloud platform itself.
  

In my opinion the SaaS model is not directly connected to cloud computing because it could be mainly also provided without a cloud infrastructure. If you take a look at the key criteria above, none of them can be really applied to Software-as-a-Service solutions. That does not mean that some applications are running on a cloud platform to reduce operational overhead and have better flexibility and scalability. It is just not needed to provide this service.

Cloud Computing Types

• Private Cloud
  The infrastructure is running internally within a company. The applications itself can be exposed to the outside world but the self-service and administration is done within a company and the internal network.
• Public Cloud
  Public Clouds are available over the internet and can be used by other companies to host their applications and services. The main public cloud solutions are Microsoft's Windows Azure, Google's App Engine and Amazon's Elastic Compute Cloud. They provide usually a pay-per-use price model where the costs depend on how much traffic and resources are used.
  
• Hybrid Cloud
  Hybrid clouds are a mix of private cloud and public cloud infrastructures. They consist of company-internal and external infrastructure which builds a federation to establish a communication between each other.
  

In the following posts I am mainly talking about private Clouds and how they can be built within a company-internal data center.