Understanding Services and Applications by Type

Infrastructure as a Service

Infrastructure as a Service (IaaS) is a cloud computing service model in which hardware is virtualized in the cloud. In this particular model, the service vendor owns the equipment: servers, storage, network infrastructure, and so forth. 

The developer interacts with the IaaS model to create virtual private servers, virtual private storage, virtual private networks, and so on, and then populates these virtual systems with the applications and services it needs to complete its solution.

IaaS Workloads

The fundamental unit of virtualized client in an IaaS deployment is called a workload. A workload simulates the ability of a certain type of real or physical server to do an amount of work. In other words it is the amount of resources allocated to a client to do an amount of work.

In cloud computing, a provisioned server called an instance is reserved by a customer, and the necessary amount of computing resources needed to achieve that type of physical server is allocated to the client's needs.

Consider a transactional eCommerce system, for which a typical stack contains the following
components:

• Web server
• Application server
• File server
• Database
• Transaction engine

This eCommerce system has several different workloads that are operating: queries against the database, processing of business logic, and serving up clients' Web pages.

 

Pods, aggregation, and silos

Workloads support a certain number of users, at which point you exceed the load that the instance sizing allows. When you reach the limit of the largest virtual machine instance possible, you must make a copy or clone of the instance to support additional users. A group of users within a particular instance is called a pod. Pods are managed by a Cloud Control System (CCS). In AWS, the CCS is the AWS Management Console.

Sizing limitations for pods need to be accounted for if you are building a large cloud-based application. Pods are aggregated into pools within an IaaS region or site called an availability zone. In very large cloud computing networks, when systems fail, they fail on a pod-by-pod basis, and often on a zone-by-zone basis. A failover system between zones gives IaaS private clouds a very high degree of availability.

When a cloud computing infrastructure isolates user clouds from each other so the management system is incapable of interoperating with other private clouds, it creates an information silo, or simply a silo. Most often, the term silo is applied to PaaS offerings such as Force.com or QuickBase, but silos often are an expression of the manner in which a cloud computing infrastructure is architected. Silos are the cloud computing equivalent of compute islands: They are processing domains that are sealed off from the outside.

When you create a private virtual network within an IaaS framework, the chances are high that you are creating a silo. Silos impose restrictions on interoperability that runs counter to the open nature of build-componentized service-oriented applications. However, that is not always a bad thing. A silo can be its own ecosystem; it can be protected and secured in ways that an open system can't be. Silos just aren't as flexible as open systems and are subject to vendor lock-in.

Defining PAAS

The Platform as a Service model describes a software environment in which a developer can create customized solutions within the context of the development tools that the platform provides. Platforms can be based on specific types of development languages, application frameworks, or other constructs.

The one example that is most quoted as a PaaS offering is Google's App Engine platform. Developers program against the App Engine using Google's published APIs. The tools for working within the development framework, as well as the structure of the file system and data stores, are defined by Google.

The difficulty with PaaS is that it locks the developer (and the customer) into a solution that is
dependent upon the platform vendor. An application written in Python against Google's API using the Google App Engine is likely to work only in that environment. There is considerable vendor lock-in associated with a PaaS solution.

Defining SAAS

The most complete cloud computing service model is one in which the computing hardware and software, as well as the solution itself, are provided by a vendor as a complete service offering. It is referred to as the Software as a Service (SaaS) model. SaaS provides the complete infrastructure, software, and solution stack as the service offering.

Examples of SaaS software for end-users are Google Gmail and Calendar, QuickBooks online, Zoho Office Suite etc.

However, many other SaaS solutions expose Application Programming Interfaces (API) to developers to allow them to create custom composite applications.These APIs may alter the security model used, the data schema, workflow characteristics, and other fundamental features of the service's expression as experienced by the user. Examples of an SaaS platform with an exposed API are Salesforce.com and Quicken.com. So SaaS does not necessarily mean that the software is static or monolithic.

SaaS characteristics
 
All Software as a Service (SaaS) applications share the following characteristics:
1. The software is available over the Internet globally through a browser on demand.

2. The typical license is subscription-based or usage-based and is billed on a recurring basis.
In a small number of cases a flat fee may be changed, often coupled with a maintenance fee.

3. The software and the service are monitored and maintained by the vendor, regardless of where all the different software components are running.There may be executable client-side code, but the user isn't responsible for maintaining that code or its interaction with the service.

4. Reduced distribution and maintenance costs and minimal end-user system costs generally make SaaS applications cheaper to use than their shrink-wrapped versions.

5. Such applications feature automated upgrades, updates, and patch management and much faster rollout of changes.

6. SaaS applications often have a much lower barrier to entry than their locally installed competitors, a known recurring cost, and they scale on demand (a property of cloud computing in general).

7. All users have the same version of the software so each user's software is compatible with
another's.

8. SaaS supports multiple users and provides a shared data model through a single-instance,
multi-tenancy model.

Open SaaS and SOA

A considerable amount of SaaS software is based on open source software. When open source software is used in a SaaS, you may hear it referred to as Open SaaS. The advantages of using open source software are that systems are much cheaper to deploy because you don't have to purchase the operating system or software, there is less vendor lock-in, and applications are more portable.

The componentized nature of SaaS solutions enables many of these solutions to support a feature called mashups. A mashup is an application that can display a Web page that shows data and supports features from two or more sources. Annotating a map such as Google maps is an example of a mashup. Mashups are considered one of the premier examples of Web 2.0, and that is technology's ability to support social network systems.

Gartner Group predicts that approximately 25 percent of all software sold by 2011 will use the SAAS model, offered either by vendors or an intermediary party, sometimes referred to as an aggregator. An aggregator bundles SaaS applications from different vendors and presents them as part of a unified platform or solution.

Salesforce.com and CRM SaaS

Perhaps the best-known example of Software as a Service (SaaS) is the Customer Relationship Management software offered by Salesforce.com whose solution offers sales, service, support, marketing, content, analytical analysis, and even collaboration through a platform called Chatter.

Salesforce.com extended its SaaS offering to allow developers to create add-on applications, essentially turning the SaaS service into a Platform as a Service (PaaS) offering called the Force.com Platform.

Applications built on Force.com are in the form of the Java variant called Apex using an XML syntax for creating user interfaces in HTML, Ajax, and Flex. Nearly a thousand applications now exist for this platform from hundreds of vendors.