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Chapter 1  Internet Era: E-Commerce 21
computing deconstructs the datacenter by distributing its functionalities across
the Internet and making those functionalities accessible as services. Following
the same evolution, the datacenter functionalities in question are evolving from
custom built and special purpose, to become services that are shared among
various users, potentially external to the legacy environment.
In any case, these components are still implemented in real datacenters,
with real hardware and real system administrators, and cloud computing (or
the functions offered by cloud computing) can be seen as a layer on top of an
existing infrastructure, so long as the infrastructure satisfied the requirements
of said services.
In the specific case of cloud computing, applications are deployed on top of this
infrastructure, interacting with the infrastructure services, either locally or through
the Internet. Optionally, applications can interact with the cloud management ser-
vices directly if they need to drive real time infrastructure changes (for example,
an application can request resources itself). This is depicted in Figure 1-9.
Consumers
Cloud Computing Services
Applications
Operations
Infrastructure Mgmt
Services
Infrastructure
Services
Cloud Computing
Implementation
Infrastructure
Management
Infrastructure
Figure 1-9: Cloud computing high-level architecture
Below is the description of cloud computing main components that are shown
in Figure 2-9, along with their responsibilities:
Cloud computing services:

Services exposed by the cloud computing imple-
mentation. This can be platform as a service (PaaS), storage as a service (SaaS),
software as a service (SaaS), and so on. These services are exposed either
through a self-service user interface (UI) or a programmatic interface.
Cloud computing implementation:

A set of components that imple-
ment the cloud computing services. This includes resource management,
resource allocation and optimization, account management and chargeback,
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