<s>
Brownout	B-General_Concept
in	O
software	B-General_Concept
engineering	I-General_Concept
is	O
a	O
technique	O
that	O
involves	O
disabling	O
certain	O
features	O
of	O
an	O
application	O
.	O
</s>
<s>
Brownout	B-General_Concept
is	O
used	O
to	O
increase	O
the	O
robustness	O
of	O
an	O
application	O
to	O
computing	O
capacity	B-General_Concept
shortage	I-General_Concept
.	O
</s>
<s>
If	O
too	O
many	O
users	O
are	O
simultaneously	O
accessing	O
an	O
application	O
hosted	O
online	B-Architecture
,	O
the	O
underlying	O
computing	B-Application
infrastructure	I-Application
may	O
become	O
overloaded	B-General_Concept
,	O
rendering	O
the	O
application	O
unresponsive	O
.	O
</s>
<s>
To	O
better	O
deal	O
with	O
such	O
a	O
situation	O
,	O
the	O
application	O
can	O
be	O
given	O
brownout	B-General_Concept
capabilities	O
:	O
The	O
application	O
will	O
disable	O
certain	O
features	O
–	O
e.g.	O
,	O
an	O
online	B-Architecture
shop	O
will	O
no	O
longer	O
display	O
recommendations	O
of	O
related	O
products	O
–	O
to	O
avoid	O
overload	O
.	O
</s>
<s>
The	O
technique	O
is	O
inspired	O
by	O
brownouts	B-General_Concept
in	O
power	O
grids	O
,	O
which	O
consists	O
in	O
reducing	O
the	O
power	O
grid	O
's	O
voltage	O
in	O
case	O
electricity	O
demand	O
exceeds	O
production	O
.	O
</s>
<s>
Similarly	O
,	O
a	O
brownout	B-General_Concept
application	O
helps	O
match	O
its	O
computing	O
capacity	O
requirements	O
to	O
what	O
is	O
available	O
on	O
the	O
target	O
infrastructure	O
.	O
</s>
<s>
Brownout	B-General_Concept
complements	O
elasticity	B-General_Concept
.	O
</s>
<s>
The	O
former	O
can	O
help	O
the	O
application	O
withstand	O
short-term	O
capacity	B-General_Concept
shortage	I-General_Concept
,	O
but	O
does	O
so	O
without	O
changing	O
the	O
capacity	O
available	O
to	O
the	O
application	O
.	O
</s>
<s>
In	O
contrast	O
,	O
elasticity	B-General_Concept
consists	O
of	O
adding	O
(	O
or	O
removing	O
)	O
capacity	O
to	O
the	O
application	O
,	O
preferably	O
in	O
advance	O
,	O
so	O
as	O
to	O
avoid	O
capacity	B-General_Concept
shortage	I-General_Concept
altogether	O
.	O
</s>
<s>
The	O
two	O
techniques	O
can	O
be	O
combined	O
;	O
e.g.	O
,	O
brownout	B-General_Concept
is	O
triggered	O
when	O
the	O
number	O
of	O
users	O
increases	O
unexpectedly	O
until	O
elasticity	B-General_Concept
can	O
be	O
triggered	O
,	O
the	O
latter	O
usually	O
requiring	O
minutes	O
to	O
show	O
an	O
effect	O
.	O
</s>
<s>
Brownout	B-General_Concept
is	O
relatively	O
non-intrusive	O
for	O
the	O
developer	O
,	O
for	O
example	O
,	O
it	O
can	O
be	O
implemented	O
as	O
an	O
advice	B-Application
in	O
aspect-oriented	O
programming	O
.	O
</s>
<s>
However	O
,	O
surrounding	O
components	O
,	O
such	O
as	O
load-balancers	O
,	O
need	O
to	O
be	O
made	O
brownout-aware	O
to	O
distinguish	O
between	O
cases	O
where	O
an	O
application	O
is	O
running	O
normally	O
and	O
cases	O
where	O
the	O
application	O
maintains	O
a	O
low	O
response	O
time	O
by	O
triggering	O
brownout	B-General_Concept
.	O
</s>
