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Cloud computing infrastructure is the hardware and enabling software that make cloud services work. In NIST’s model, it has a physical layer—typically servers, storage, and networks—and an abstraction layer of software deployed across that hardware to provide cloud capabilities. That distinction matters: cloud infrastructure is more than a collection of servers or a data center.
What does cloud computing infrastructure mean?
NIST defines cloud computing as a model for convenient, on-demand network access to a shared pool of configurable computing resources—such as networks, servers, storage, applications, and services—that can be rapidly provisioned and released with minimal management effort or provider interaction. The definition appears in NIST Special Publication 800-145, published in September 2011 by Peter Mell and Timothy Grance.
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Cloud infrastructure is the underlying combination of physical resources and the software layer that abstracts and coordinates them. NIST’s definition gives readers a framework for identifying cloud computing; it is not a prescription for how a particular organization must build or operate its systems.
What are the two layers of cloud infrastructure?
Physical layer
The physical layer consists of the hardware resources that support cloud services, typically servers, storage, and network equipment. These components provide computing capacity, data storage, and connectivity.
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Abstraction layer
The abstraction layer is software deployed across the physical layer. It presents and manages the underlying resources so they can be provisioned, pooled, scaled, and measured as cloud capabilities. In NIST’s conceptual model, this layer sits above the physical one; the hardware alone does not account for the cloud operating model.
What makes infrastructure “cloud”?
NIST identifies five essential characteristics. Together, they describe the way cloud resources are made available and managed—not a guarantee of unlimited capacity, identical prices, or a particular provider’s performance.
- On-demand self-service: A consumer can automatically provision capabilities such as server time or network storage without human interaction with the provider for each request.
- Broad network access: Capabilities are available over a network through standard mechanisms that work across different kinds of client platforms.
- Resource pooling: The provider pools resources to serve multiple consumers and dynamically assigns or reassigns physical and virtual resources as demand changes. Consumers generally do not control or know the exact resource location, though they may be able to select a broader location, such as a country, state, or data center.
- Rapid elasticity: Capabilities can be provisioned and released, sometimes automatically, to scale outward or inward with demand.
- Measured service: Resource use is metered at a level appropriate to the service, monitored, controlled, and reported to make usage transparent.
How do cloud service models differ?
Service models describe the capability a consumer receives and how much of the underlying system the consumer controls. NIST distinguishes three:
| Service model | What the consumer gets | Consumer control |
|---|---|---|
| Software as a Service (SaaS) | Use of provider applications running on cloud infrastructure. | The provider manages the underlying infrastructure. The consumer may have limited configuration options specific to their use of the application. |
| Platform as a Service (PaaS) | A platform for deploying applications using the provider’s supported languages, libraries, services, and tools. | The consumer controls deployed applications and may control some application-hosting settings, but not the underlying infrastructure. |
| Infrastructure as a Service (IaaS) | Fundamental computing resources, including processing, storage, and networks, on which the consumer can deploy and run software such as operating systems and applications. | The consumer controls operating systems, storage, and deployed applications, and may have limited control over selected networking components. |
The practical distinction is what the consumer uses or deploys: a provider’s application with SaaS, their own applications on a supported platform with PaaS, or fundamental computing resources with IaaS. NIST SP 500-322 offers guidance for assessing whether a service aligns with these categories: Evaluation of Cloud Computing Services Based on NIST SP 800-145.
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How do cloud deployment models differ?
Deployment models describe who the infrastructure is for and how separate cloud environments are arranged. They answer a different question from SaaS, PaaS, and IaaS, which describe the service capability.
| Deployment model | Who uses it and how it is arranged |
|---|---|
| Private cloud | Provisioned for the exclusive use of one organization, which may have multiple internal consumers. It may be on or off premises and operated by the organization, a third party, or both. |
| Community cloud | Provisioned for the exclusive use of a specific community of organizations with shared concerns, such as mission, security, policy, or compliance. |
| Public cloud | Provisioned for open use by the general public and operated by a business, academic, government, or combined organization. |
| Hybrid cloud | A composition of two or more distinct private, community, or public clouds. They remain separate entities but are connected to enable data and application portability. |
Hybrid is a deployment model, not a service model parallel to IaaS or PaaS. Nor does “cloud” by itself specify one ownership arrangement: NIST’s private and community models are restricted to a defined organization or community, while public cloud is open for general use.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How can you assess whether a service fits the cloud definition?
Use the characteristics as a practical checklist, then classify the service on the two separate axes: service model and deployment model.
- Check the resource pool: Does the service provide network access to a shared pool of configurable resources?
- Check provisioning: Can capabilities be provisioned and released rapidly with minimal management effort or provider interaction?
- Check the five characteristics: Look for on-demand self-service, broad network access, resource pooling, rapid elasticity, and measured service.
- Classify the capability: Decide whether the consumer uses provider software (SaaS), deploys applications to a provider platform (PaaS), or provisions fundamental resources (IaaS).
- Classify the arrangement: Separately determine whether the environment is private, community, public, or hybrid.
NIST describes SP 800-145 as a baseline for broad comparison and discussion, not as a rule that constrains a specific deployment, service delivery, or business operation. Its original publication notice explains that agencies and companies can use the definition to assess how closely an IT implementation meets the cloud characteristics and models: NIST’s publication announcement.
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