openstack-manuals/doc/arch-design/source/generalpurpose-user-requirements.rst

User requirements

When building a general purpose cloud, you should follow the Infrastructure-as-a-Service (IaaS) model; a platform best suited for use cases with simple requirements. General purpose cloud user requirements are not complex. However, it is important to capture them even if the project has minimum business and technical requirements, such as a proof of concept (PoC), or a small lab platform.

Note

The following user considerations are written from the perspective of the cloud builder, not from the perspective of the end user.

Business requirements

Cost

Financial factors are a primary concern for any organization. Cost is an important criterion as general purpose clouds are considered the baseline from which all other cloud architecture environments derive. General purpose clouds do not always provide the most cost-effective environment for specialized applications or situations. Unless razor-thin margins and costs have been mandated as a critical factor, cost should not be the sole consideration when choosing or designing a general purpose architecture.

Time to market

The ability to deliver services or products within a flexible time frame is a common business factor when building a general purpose cloud. Delivering a product in six months instead of two years is a driving force behind the decision to build general purpose clouds. General purpose clouds allow users to self-provision and gain access to compute, network, and storage resources on-demand thus decreasing time to market.

Revenue opportunity

Revenue opportunities for a cloud will vary greatly based on the intended use case of that particular cloud. Some general purpose clouds are built for commercial customer facing products, but there are alternatives that might make the general purpose cloud the right choice.

Technical requirements

Technical cloud architecture requirements should be weighted against the business requirements.

Performance

As a baseline product, general purpose clouds do not provide optimized performance for any particular function. While a general purpose cloud should provide enough performance to satisfy average user considerations, performance is not a general purpose cloud customer driver.

No predefined usage model

The lack of a pre-defined usage model enables the user to run a wide variety of applications without having to know the application requirements in advance. This provides a degree of independence and flexibility that no other cloud scenarios are able to provide.

On-demand and self-service application

By definition, a cloud provides end users with the ability to self-provision computing power, storage, networks, and software in a simple and flexible way. The user must be able to scale their resources up to a substantial level without disrupting the underlying host operations. One of the benefits of using a general purpose cloud architecture is the ability to start with limited resources and increase them over time as the user demand grows.

Public cloud

For a company interested in building a commercial public cloud offering based on OpenStack, the general purpose architecture model might be the best choice. Designers are not always going to know the purposes or workloads for which the end users will use the cloud.

Internal consumption (private) cloud

Organizations need to determine if it is logical to create their own clouds internally. Using a private cloud, organizations are able to maintain complete control over architectural and cloud components.

Note

Users will want to combine using the internal cloud with access to an external cloud. If that case is likely, it might be worth exploring the possibility of taking a multi-cloud approach with regard to at least some of the architectural elements.

Designs that incorporate the use of multiple clouds, such as a private cloud and a public cloud offering, are described in the "Multi-Cloud" scenario, see multi-site.

Security

Security should be implemented according to asset, threat, and vulnerability risk assessment matrices. For cloud domains that require increased computer security, network security, or information security, a general purpose cloud is not considered an appropriate choice.