This document gives an overview of a Private Cloud Reference Model. For the purposes of this document, a Reference Model is defined as the problem definition, requirements, and scope for a specific domain including the identification of all layers (or subdomains)
and any interactions or dependencies between the components.
This document is part of a collection of documents that comprise the Reference Architecture for Private Cloud
document set. The Solution for Private Cloud is a community collaboration project. Please feel free to edit this document to improve the quality of this document. If you would like to be recognized for your work on improving this document, please include
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An updated version of this article is now available as part of the
Cloud Services Foundation Reference Architecture article set.
This Reference Model forms the basis, or cornerstone, for all Reference Architecture in a Private Cloud. It not only defines the domain but also sets
taxonomy and drives coherency of approach amongst the many authors who contribute to the Private Cloud Reference Architecture documentation set. Every contributor and reviewer of the Reference Architecture
documentation should use the Reference Model to understand the broad landscape of the problem domain before being able to decide if the existing guidance meets their needs or identify what new guidance may be required.
The Reference Model will initially be depicted as a single diagram and the remainder of the document will decompose each layer and describe its components.
This is a general purpose document that provides foundational context and approach for the development of Reference Architecture documentation. Therefore, the first audience for this document are all those people who are involved in the development of any Private
Cloud Reference Architecture. All reviewers of the Reference Architecture materials can use this document to determine “fit for purpose” for their materials. The applicability of this guidance is much broader than the development activity as any architect,
service manager, or technical decision maker will benefit from an understanding of the problem domain and the approach to producing the Reference Architecture.
The Private Cloud Reference Model defines the scope and the problem space for its domain. The model acts as the “guide-rails” to assist architects’ efforts to holistically address the development of a private cloud architecture. Additionally, it provides
a common vocabulary and shared understanding across all constituencies.
The Reference Model below depicts a number of layers, which are further decomposed into specific problem spaces or components.
Figure 1: The Private Cloud Reference Model
The Reference Model is split into the following layers:
It is a deliberate attempt to blend technology and process (for example, Information Technology Infrastructure Library (ITIL)) perspectives because Cloud Computing is as much about the Service Management as
it is about the technologies involved in it.
At first it may not seem much different from traditional IT; but remember, this is not a Reference Architecture, it is a Reference Model and is defined as the
problem domain. Many of IT’s problems continue to be the same, from both a technology and operational perspective; however, the differences now include some enabling technologies and radical approaches
based on the experience and concepts associated with Cloud Computing. From an operational perspective, the desire to adopt good IT Service Management practices has also been around for a long time. But many organizations have not been effective in implementing
these best practices and this hinders their success. Cloud Computing is driving a new emphasis on operational rigor, casting a fresh light on best-practices and forcing IT to re-think some of its fundamental concepts.
The layers are further defined as follows:
The Service Delivery layer is the interface between business and IT. It serves as the conduit for translating business requirements into IT services and is responsible for managing ongoing delivery of those services. These capabilities are common to all
services: Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS).
Figure 2: Service Delivery Layer Components
As the primary interface with the business, the Service Delivery Layer is expected to know or obtain answers the following questions:
With these questions in mind, there are two main problems within the Service Layer that IT must address:
An organization must adopt the following private cloud principles in order to meet the business objectives of a cloud-like
The components of the Service Delivery Layer are:
The Software Layer provides the business applications with solution-specific runtime components necessary to deliver a business service. It will consume hypervisor services from the Infrastructure Layer and may consume application services from the Platform
Layer. The Software Layer provides interfaces to end-users.
The Platform Layer provides application services to the Software Layer and consumes hypervisor services from the Infrastructure Layer. Platform Layer interfaces will vary; some examples of Platform Layer interface include Hypertext Transfer Protocol (HTTP)
and Representational State Transfer (REST).
The Infrastructure Layer provides hypervisor services (VM resources) to the Platform and Software Layers. It defines the capabilities necessary for these VMs to execute; it includes hypervisor, physical servers, network devices, storage systems, and facilities
(which include space, power, cooling, and physical interconnects).
Figure 3: Infrastructure Layer Components
Infrastructure Layer components include:
The Service Operations Layer defines the operational processes and procedures necessary to deliver IT as a Service. This layer uses IT Service Management concepts that can be found in prevailing best practice such as ITIL or Microsoft Operations Framework
The main focus of the Service Operations Layer is to execute the business requirements defined at the Service Delivery layer. Cloud-like service attributes cannot be achieved through technology alone; mature IT service management is also required.
The Service Operations capabilities are common to all three services; IaaS, PaaS, and SaaS.
Figure 4: Service Operations Layer Components
The components of the Service Operations Layer include:
The Management Layer defines the capabilities required to execute and implement the Operation and Service Layer processes and procedures to support IaaS, PaaS, and SaaS. These capabilities are incremental moving up through the Infrastructure, Platform and
Figure 5: Management Layer Components Related to Infrastructure
The components of the Management Layer related to the Infrastructure Layer are:
As this content series continues each element of the Reference Model will be expanded to expose the details of each layer resulting in a complete Reference Architecture for Private Cloud. Note that that Security (which includes identity and access management)
is not represented in the Reference Model. This was not by omission but rather recognition that the security domain is a cross-cutting concern that influences every aspect of the architecture. Rather than show a security block with arrows throughout the diagram
we just recognize the cross cutting nature of security on the architecture and will address it in the Cloud Security Architecture document set and as each layer is expanded.
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Cloud and Data Center Solutions Hub.
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