<s>
Infrastructure	B-General_Concept
as	I-General_Concept
a	I-General_Concept
service	I-General_Concept
(	O
IaaS	B-General_Concept
)	O
is	O
a	O
cloud	B-Architecture
computing	I-Architecture
service	O
model	O
by	O
means	O
of	O
which	O
computing	O
resources	O
are	O
supplied	O
by	O
a	O
cloud	B-Architecture
services	I-Architecture
provider	I-Architecture
.	O
</s>
<s>
The	O
IaaS	B-General_Concept
vendor	O
provides	O
the	O
storage	O
,	O
network	O
,	O
servers	O
,	O
and	O
virtualization	B-General_Concept
(	O
which	O
mostly	O
refers	O
,	O
in	O
this	O
case	O
,	O
to	O
emulating	O
computer	O
hardware	O
)	O
.	O
</s>
<s>
This	O
service	O
enables	O
users	O
to	O
free	O
themselves	O
from	O
maintaining	O
an	O
on-premises	O
data	B-Operating_System
center	I-Operating_System
.	O
</s>
<s>
The	O
IaaS	B-General_Concept
provider	O
is	O
hosting	O
these	O
resources	O
in	O
either	O
the	O
public	O
cloud	O
(	O
meaning	O
users	O
share	O
the	O
same	O
hardware	O
,	O
storage	O
,	O
and	O
network	O
devices	O
with	O
other	O
users	O
)	O
,	O
the	O
private	O
cloud	O
(	O
meaning	O
users	O
do	O
not	O
share	O
these	O
resources	O
)	O
,	O
or	O
the	O
hybrid	O
cloud	O
(	O
combination	O
of	O
both	O
)	O
.	O
</s>
<s>
It	O
provides	O
the	O
customer	O
with	O
high-level	O
APIs	B-General_Concept
used	O
to	O
dereference	O
various	O
low-level	O
details	O
of	O
underlying	O
network	O
infrastructure	O
like	O
backup	O
,	O
data	O
partitioning	O
,	O
scaling	O
,	O
security	O
,	O
physical	O
computing	O
resources	O
,	O
etc	O
.	O
</s>
<s>
A	O
hypervisor	B-Operating_System
,	O
such	O
as	O
Xen	B-Operating_System
,	O
Oracle	B-Operating_System
VirtualBox	I-Operating_System
,	O
Oracle	B-Application
VM	I-Application
,	O
KVM	B-Application
,	O
VMware	O
ESX/ESXi	O
,	O
or	O
Hyper-V	O
runs	O
the	O
virtual	B-Architecture
machines	I-Architecture
as	O
guests	O
.	O
</s>
<s>
Pools	O
of	O
hypervisors	B-Operating_System
within	O
the	O
cloud	O
operational	O
system	O
can	O
support	O
large	O
numbers	O
of	O
virtual	B-Architecture
machines	I-Architecture
as	O
well	O
as	O
the	O
ability	O
to	O
scale	O
services	O
up	O
and	O
down	O
according	O
to	O
customers	O
 '	O
varying	O
requirements	O
.	O
</s>
<s>
Typically	O
IaaS	B-General_Concept
involves	O
the	O
use	O
of	O
a	O
cloud	B-Application
orchestration	I-Application
technology	I-Application
like	O
OpenStack	B-Application
,	O
Apache	B-General_Concept
CloudStack	I-General_Concept
or	O
OpenNebula	B-Language
.	O
</s>
<s>
It	O
manages	O
the	O
creation	O
of	O
a	O
virtual	B-Architecture
machine	I-Architecture
and	O
decides	O
on	O
the	O
hypervisor	B-Operating_System
(	O
i.e.	O
</s>
<s>
An	O
alternative	O
to	O
hypervisors	B-Operating_System
is	O
Linux	B-Operating_System
containers	B-Application
,	O
which	O
run	O
in	O
isolated	O
partitions	O
of	O
a	O
single	O
Linux	B-Operating_System
kernel	I-Operating_System
running	O
directly	O
on	O
the	O
physical	O
hardware	O
.	O
</s>
<s>
Linux	B-Operating_System
cgroups	B-Application
and	O
namespaces	O
are	O
the	O
underlying	O
Linux	B-Operating_System
kernel	I-Operating_System
technologies	O
used	O
to	O
isolate	O
,	O
secure	O
and	O
manage	O
the	O
containers	B-Application
.	O
</s>
<s>
Containerisation	O
offers	O
higher	O
performance	O
than	O
virtualization	B-General_Concept
because	O
there	O
is	O
no	O
hypervisor	B-Operating_System
overhead	O
.	O
</s>
<s>
IaaS	B-General_Concept
clouds	O
often	O
offer	O
additional	O
resources	O
such	O
as	O
a	O
virtual-machine	O
disk-image	B-Application
library	O
,	O
raw	O
block	B-General_Concept
storage	I-General_Concept
,	O
file	O
or	O
object	B-Application
storage	I-Application
,	O
firewalls	O
,	O
load	O
balancers	O
,	O
IP	O
addresses	O
,	O
virtual	B-General_Concept
local	I-General_Concept
area	I-General_Concept
networks	I-General_Concept
(	O
VLANs	B-General_Concept
)	O
,	O
and	O
software	O
bundles	O
.	O
</s>
<s>
The	O
NIST	O
's	O
definition	O
of	O
cloud	B-Architecture
computing	I-Architecture
defines	O
infrastructure	B-General_Concept
as	I-General_Concept
a	I-General_Concept
service	I-General_Concept
like	O
:	O
</s>
<s>
According	O
to	O
the	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
,	O
the	O
most	O
basic	O
cloud-service	O
model	O
offered	O
by	O
the	O
providers	O
is	O
IT	B-Application
infrastructure	I-Application
–	O
virtual	B-Architecture
machines	I-Architecture
and	O
other	O
resources	O
–	O
as	O
a	O
service	O
to	O
subscribers	O
.	O
</s>
<s>
IaaS-cloud	O
providers	O
supply	O
these	O
resources	O
on-demand	O
from	O
the	O
large	O
pools	O
of	O
equipment	O
installed	O
in	O
data	B-Operating_System
centers	I-Operating_System
.	O
</s>
<s>
For	O
wide-area	O
connectivity	O
,	O
customers	O
can	O
use	O
either	O
the	O
Internet	O
or	O
carrier	B-General_Concept
clouds	I-General_Concept
(	O
dedicated	O
virtual	B-Application
private	I-Application
networks	I-Application
)	O
.	O
</s>
<s>
To	O
deploy	O
their	O
applications	O
,	O
cloud	B-Architecture
users	I-Architecture
install	O
operating-system	O
images	O
and	O
the	O
application	O
software	O
on	O
the	O
cloud	O
infrastructure	O
.	O
</s>
<s>
Cloud	O
providers	O
typically	O
bill	O
IaaS	B-General_Concept
services	O
on	O
a	O
utility	O
computing	O
basis	O
:	O
cost	O
reflects	O
the	O
number	O
of	O
resources	O
allocated	O
and	O
consumed	O
.	O
</s>
