Cloud Software Hosting Alternatives
Virtualization also may be used in SaaS architectures, either in addition to multi-tenancy, or in place of it. One of the principal benefits of virtualization is that it can increase the system's capacity without additional programming. On the other hand, a considerable amount of programming may be required to construct a more efficient, multi-tenant application. Combining multi-tenancy and virtualization provides still greater flexibility to tune the system for optimal performance. In addition to full operating system-level virtualization, other virtualization techniques applied to SaaS include application virtualization and virtual appliances.
Various types of software components and frameworks may be employed in the development of SaaS applications. These tools can reduce the time to market and cost of converting a traditional on-premise software product or building and deploying a new SaaS solution. Examples include components for subscription management, grid computing software, web application frameworks, and complete SaaS platform products.
According to Microsoft, cloud architectures generally can be classified as belonging to one of four "maturity levels," whose key attributes are configurability, multi-tenant efficiency, and scalability. Each level is distinguished from the previous one by the addition of one of those three attributes:
- Level 1 - Ad-Hoc/Custom: At the first level of maturity, each customer has its own customized version of the hosted application and runs its own instance of the application on the host's servers. Migrating a traditional non-networked or client-server application to this level of SaaS typically requires the least development effort and reduces operating costs by consolidating server hardware and administration.
- Level 2 - Configurable: The second maturity level provides greater program flexibility through configurable metadata, so that many customers can use separate instances of the same application code. This allows the vendor to meet the different needs of each customer through detailed configuration options, while simplifying maintenance and updating of a common code base.
- Level 3 - Configurable, Multi-Tenant-Efficient: The third maturity level adds multi-tenancy to the second level, so that a single program instance serves all customers. This approach enables more efficient use of server resources without any apparent difference to the end user, but ultimately is limited in its scalability.
- Level 4 - Scalable, Configurable, Multi-Tenant-Efficient: At the fourth and final SaaS maturity level, scalability is added through a multitier architecture supporting a load-balanced farm of identical application instances, running on a variable number of servers. The system's capacity can be increased or decreased to match demand by adding or removing servers, without the need for any further alteration of application software architecture.