<s>
Software	B-Application
multitenancy	B-Architecture
is	O
a	O
software	B-Architecture
architecture	I-Architecture
in	O
which	O
a	O
single	O
instance	O
of	O
software	B-Application
runs	O
on	O
a	O
server	O
and	O
serves	O
multiple	O
tenants	O
.	O
</s>
<s>
A	O
tenant	O
is	O
a	O
group	O
of	O
users	O
who	O
share	O
a	O
common	O
access	O
with	O
specific	O
privileges	O
to	O
the	B-Application
software	I-Application
instance	O
.	O
</s>
<s>
With	O
a	O
multitenant	B-Architecture
architecture	O
,	O
a	O
software	B-Application
application	I-Application
is	O
designed	O
to	O
provide	O
every	O
tenant	O
a	O
dedicated	O
share	O
of	O
the	O
instance	O
-	O
including	O
its	O
data	O
,	O
configuration	O
,	O
user	O
management	O
,	O
tenant	O
individual	O
functionality	O
and	O
non-functional	O
properties	O
.	O
</s>
<s>
Multitenancy	B-Architecture
contrasts	O
with	O
multi-instance	O
architectures	O
,	O
where	O
separate	O
software	B-Application
instances	O
operate	O
on	O
behalf	O
of	O
different	O
tenants	O
.	O
</s>
<s>
Some	O
commentators	O
regard	O
multitenancy	B-Architecture
as	O
an	O
important	O
feature	O
of	O
cloud	B-Architecture
computing	I-Architecture
.	O
</s>
<s>
Multitenant	B-Architecture
applications	O
have	O
evolved	O
from	O
—	O
and	O
combine	O
some	O
characteristics	O
of	O
—	O
three	O
types	O
of	O
services	O
:	O
</s>
<s>
Timesharing	B-General_Concept
:	O
From	O
the	O
1960s	O
companies	O
rented	O
space	O
and	O
processing	O
power	O
on	O
mainframe	O
computers	O
(	O
time-sharing	B-General_Concept
)	O
to	O
reduce	O
computing	O
expenses	O
.	O
</s>
<s>
Depending	O
on	O
the	O
limitation	O
of	O
the	O
underlying	O
application	O
,	O
ASPs	O
were	O
forced	O
to	O
host	O
applications	O
on	O
separate	O
machines	O
(	O
if	O
multiple	O
instances	O
of	O
the	O
applications	O
could	O
not	O
be	O
executed	O
in	O
the	O
same	O
physical	O
machine	O
)	O
or	O
as	O
separate	O
processes	B-Operating_System
.	O
</s>
<s>
Multitenant	B-Architecture
applications	O
represent	O
a	O
more	O
mature	O
architecture	O
which	O
enables	O
a	O
similar	O
service	O
with	O
lower	O
operational	O
cost	O
.	O
</s>
<s>
Web	B-Application
applications	I-Application
:	O
Popular	O
consumer-oriented	O
web	B-Application
applications	I-Application
(	O
such	O
as	O
Hotmail	B-Operating_System
)	O
developed	O
with	O
a	O
single	O
application	O
instance	O
serving	O
all	O
customers	O
.	O
</s>
<s>
Multitenant	B-Architecture
applications	O
represent	O
a	O
natural	O
evolution	O
from	O
this	O
model	O
,	O
offering	O
additional	O
customization	O
to	O
groups	O
of	O
users	O
within	O
(	O
say	O
)	O
the	O
same	O
client	O
organization	O
.	O
</s>
<s>
In	O
a	O
multitenancy	B-Architecture
environment	O
,	O
multiple	O
customers	O
share	O
the	O
same	O
application	O
,	O
running	O
on	O
the	O
same	O
operating	O
system	O
,	O
on	O
the	O
same	O
hardware	O
,	O
with	O
the	O
same	O
data-storage	O
mechanism	O
.	O
</s>
<s>
Compare	O
this	O
with	O
virtualization	B-General_Concept
where	O
components	O
are	O
transformed	O
,	O
enabling	O
each	O
customer	O
application	O
to	O
appear	O
to	O
run	O
on	O
a	O
separate	O
virtual	O
machine	O
.	O
</s>
<s>
Some	O
companies	O
actively	O
promote	O
the	O
principle	O
of	O
multitenancy	B-Architecture
and	O
use	O
it	O
as	O
a	O
source	O
of	O
competitive	O
differentiation	O
.	O
</s>
<s>
The	O
use	O
of	O
multitenancy	B-Architecture
is	O
increasing	O
day	O
by	O
day	O
.	O
</s>
<s>
Multitenancy	B-Architecture
allows	O
for	O
cost	O
savings	O
over	O
and	O
above	O
the	O
basic	O
economies	O
of	O
scale	O
achievable	O
from	O
consolidating	O
IT	O
resources	O
into	O
a	O
single	O
operation	O
.	O
</s>
<s>
Multitenancy	B-Architecture
reduces	O
this	O
overhead	O
by	O
spreading	O
it	O
over	O
many	O
customers	O
.	O
</s>
<s>
Further	O
cost	O
savings	O
may	O
come	O
from	O
licensing	O
costs	O
of	O
the	O
underlying	O
software	B-Application
(	O
such	O
as	O
operating	O
systems	O
and	O
database	O
management	O
systems	O
)	O
.	O
</s>
<s>
Put	O
crudely	O
,	O
if	O
you	O
can	O
run	O
everything	O
on	O
a	O
single	O
software	B-Application
instance	O
,	O
you	O
only	O
have	O
to	O
buy	O
one	O
software	B-License
license	I-License
.	O
</s>
<s>
The	O
cost	O
savings	O
can	O
be	O
eclipsed	O
by	O
the	O
difficulty	O
of	O
scaling	B-Architecture
the	O
single	O
instance	O
as	O
demand	O
grows	O
-	O
increasing	O
the	O
performance	O
of	O
the	O
instance	O
on	O
a	O
single	O
server	O
can	O
only	O
be	O
done	O
by	O
buying	O
faster	O
hardware	O
,	O
such	O
as	O
fast	O
CPUs	O
,	O
more	O
memory	O
,	O
and	O
faster	O
disk	O
systems	O
,	O
and	O
typically	O
these	O
costs	O
grow	O
faster	O
than	O
if	O
the	O
load	O
was	O
split	O
between	O
multiple	O
servers	O
with	O
roughly	O
the	O
same	O
aggregate	O
capacity	O
.	O
</s>
<s>
In	O
addition	O
,	O
development	O
of	O
multitenant	B-Architecture
systems	O
is	O
more	O
complex	O
,	O
and	O
security	O
testing	O
is	O
more	O
stringent	O
owing	O
to	O
the	O
fact	O
that	O
multiple	O
customers	O
 '	O
data	O
is	O
being	O
commingled	O
.	O
</s>
<s>
One	O
of	O
the	O
most	O
compelling	O
reasons	O
for	O
vendors/ISVs	O
to	O
utilize	O
multitenancy	B-Architecture
is	O
for	O
the	O
inherent	O
data	O
aggregation	O
benefits	O
.	O
</s>
<s>
Instead	O
of	O
collecting	O
data	O
from	O
multiple	O
data	O
sources	O
,	O
with	O
potentially	O
different	O
database	B-Application
schemas	I-Application
,	O
all	O
data	O
for	O
all	O
customers	O
is	O
stored	O
in	O
a	O
single	O
database	B-Application
schema	I-Application
.	O
</s>
<s>
Thus	O
,	O
running	O
queries	O
across	O
customers	O
,	O
mining	B-Application
data	I-Application
,	O
and	O
looking	O
for	O
trends	O
is	O
much	O
simpler	O
.	O
</s>
<s>
This	O
reason	O
is	O
probably	O
overhyped	O
as	O
one	O
of	O
the	O
core	O
multitenancy	B-Architecture
requirements	O
is	O
the	O
need	O
to	O
prevent	O
Service	O
Provider	O
access	O
to	O
customer	O
(	O
tenant	O
)	O
information	O
.	O
</s>
<s>
Because	O
of	O
the	O
additional	O
customization	O
complexity	O
and	O
the	O
need	O
to	O
maintain	O
per-tenant	O
metadata	O
,	O
multitenant	B-Architecture
applications	O
require	O
a	O
larger	O
development	O
effort	O
.	O
</s>
<s>
Multitenancy	B-Architecture
simplifies	O
the	O
release	O
management	O
process	O
.	O
</s>
<s>
With	O
the	O
multitenant	B-Architecture
model	O
,	O
the	O
package	O
typically	O
only	O
needs	O
to	O
be	O
installed	O
on	O
a	O
single	O
server	O
.	O
</s>
<s>
At	O
the	O
same	O
time	O
,	O
multitenancy	B-Architecture
increases	O
the	O
risks	O
and	O
impacts	O
inherent	O
in	O
applying	O
a	O
new	O
release	O
version	O
.	O
</s>
<s>
As	O
there	O
is	O
a	O
single	O
software	B-Application
instance	O
serving	O
multiple	O
tenants	O
,	O
an	O
update	O
on	O
this	O
instance	O
may	O
cause	O
downtime	O
for	O
all	O
tenants	O
even	O
if	O
the	O
update	O
is	O
requested	O
and	O
useful	O
for	O
only	O
one	O
tenant	O
.	O
</s>
<s>
Multitenant	B-Architecture
applications	O
are	O
typically	O
required	O
to	O
provide	O
a	O
high	O
degree	O
of	O
customization	O
to	O
support	O
each	O
target	O
organization	O
's	O
needs	O
.	O
</s>
<s>
Branding	O
:	O
allowing	O
each	O
organization	O
to	O
customize	O
the	O
look-and-feel	O
of	O
the	O
application	O
to	O
match	O
their	O
corporate	O
branding	O
(	O
often	O
referred	O
to	O
as	O
a	O
distinct	O
"	O
skin	B-Application
"	O
)	O
.	O
</s>
<s>
Workflow	B-Operating_System
:	O
accommodating	O
differences	O
in	O
workflow	B-Operating_System
to	O
be	O
used	O
by	O
a	O
wide	O
range	O
of	O
potential	O
customers	O
.	O
</s>
<s>
Extensions	O
to	O
the	O
data	B-Application
model	I-Application
:	O
supporting	O
an	O
extensible	O
data	B-Application
model	I-Application
to	O
give	O
customers	O
the	O
ability	O
to	O
customize	O
the	O
data	O
elements	O
managed	O
by	O
the	O
application	O
to	O
meet	O
their	O
specific	O
needs	O
.	O
</s>
<s>
Multitenant	B-Architecture
applications	O
are	O
expected	O
to	O
provide	O
adequate	O
security	O
,	O
robustness	B-Application
and	O
performance	O
between	O
multiple	O
tenants	O
which	O
is	O
provided	O
by	O
the	O
layers	O
below	O
the	O
application	O
in	O
case	O
of	O
multi-instance	O
applications	O
.	O
</s>
<s>
The	O
costs	O
of	O
redesigning	O
applications	O
for	O
multitenancy	B-Architecture
can	O
be	O
significant	O
,	O
especially	O
for	O
software	B-Application
vendors	O
who	O
continue	O
to	O
offer	O
an	O
on-premises	O
single	O
tenant	O
version	O
of	O
their	O
product	O
.	O
</s>
<s>
An	O
increasingly	O
viable	O
alternative	O
route	O
to	O
multitenancy	B-Architecture
that	O
eliminates	O
the	O
need	O
for	O
significant	O
architectural	O
change	O
is	O
to	O
use	O
virtualization	B-General_Concept
technology	I-General_Concept
to	O
host	O
multiple	O
isolated	O
instances	O
of	O
an	O
application	O
on	O
one	O
or	O
more	O
servers	O
.	O
</s>
<s>
Indeed	O
,	O
when	O
applications	O
are	O
repackaged	O
as	O
virtual	B-Application
appliances	I-Application
the	O
same	O
appliance	O
image	O
can	O
be	O
deployed	O
in	O
ISV	O
hosted	O
,	O
on-premises	O
or	O
trusted-third	O
party	O
locations	O
and	O
even	O
migrated	O
from	O
one	O
deployment	O
site	O
to	O
another	O
over	O
time	O
.	O
</s>
