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

User requirements

Defining user requirements for a massively scalable OpenStack design architecture dictates approaching the design from two different, yet sometimes opposing, perspectives: the cloud user, and the cloud operator. The expectations and perceptions of the consumption and management of resources of a massively scalable OpenStack cloud from these two perspectives are distinctly different.

Massively scalable OpenStack clouds have the following user requirements:

• The cloud user expects repeatable, dependable, and deterministic processes for launching and deploying cloud resources. You could deliver this through a web-based interface or publicly available API endpoints. All appropriate options for requesting cloud resources must be available through some type of user interface, a command-line interface (CLI), or API endpoints.
• Cloud users expect a fully self-service and on-demand consumption model. When an OpenStack cloud reaches the massively scalable size, expect consumption as a service in each and every way.
• For a user of a massively scalable OpenStack public cloud, there are no expectations for control over security, performance, or availability. Users expect only SLAs related to uptime of API services, and very basic SLAs for services offered. It is the user's responsibility to address these issues on their own. The exception to this expectation is the rare case of a massively scalable cloud infrastructure built for a private or government organization that has specific requirements.

The cloud user's requirements and expectations that determine the cloud design focus on the consumption model. The user expects to consume cloud resources in an automated and deterministic way, without any need for knowledge of the capacity, scalability, or other attributes of the cloud's underlying infrastructure.

Operator requirements

While the cloud user can be completely unaware of the underlying infrastructure of the cloud and its attributes, the operator must build and support the infrastructure for operating at scale. This presents a very demanding set of requirements for building such a cloud from the operator's perspective:

• Everything must be capable of automation. For example, everything from compute hardware, storage hardware, networking hardware, to the installation and configuration of the supporting software. Manual processes are impractical in a massively scalable OpenStack design architecture.
• The cloud operator requires that capital expenditure (CapEx) is minimized at all layers of the stack. Operators of massively scalable OpenStack clouds require the use of dependable commodity hardware and freely available open source software components to reduce deployment costs and operational expenses. Initiatives like OpenCompute (more information available at http://www.opencompute.org) provide additional information and pointers. To cut costs, many operators sacrifice redundancy. For example, using redundant power supplies, network connections, and rack switches.
• Companies operating a massively scalable OpenStack cloud also require that operational expenditures (OpEx) be minimized as much as possible. We recommend using cloud-optimized hardware when managing operational overhead. Some of the factors to consider include power, cooling, and the physical design of the chassis. Through customization, it is possible to optimize the hardware and systems for this type of workload because of the scale of these implementations.
• Massively scalable OpenStack clouds require extensive metering and monitoring functionality to maximize the operational efficiency by keeping the operator informed about the status and state of the infrastructure. This includes full scale metering of the hardware and software status. A corresponding framework of logging and alerting is also required to store and enable operations to act on the meters provided by the metering and monitoring solutions. The cloud operator also needs a solution that uses the data provided by the metering and monitoring solution to provide capacity planning and capacity trending analysis.
• Invariably, massively scalable OpenStack clouds extend over several sites. Therefore, the user-operator requirements for a multi-site OpenStack architecture design are also applicable here. This includes various legal requirements; other jurisdictional legal or compliance requirements; image consistency-availability; storage replication and availability (both block and file/object storage); and authentication, authorization, and auditing (AAA). See multi-site for more details on requirements and considerations for multi-site OpenStack clouds.
• The design architecture of a massively scalable OpenStack cloud must address considerations around physical facilities such as space, floor weight, rack height and type, environmental considerations, power usage and power usage efficiency (PUE), and physical security.