<s>
Autoscaling	B-General_Concept
,	O
also	O
spelled	O
auto	B-General_Concept
scaling	I-General_Concept
or	O
auto-scaling	B-General_Concept
,	O
and	O
sometimes	O
also	O
called	O
automatic	B-General_Concept
scaling	I-General_Concept
,	O
is	O
a	O
method	O
used	O
in	O
cloud	B-Architecture
computing	I-Architecture
that	O
dynamically	O
adjusts	O
the	O
amount	O
of	O
computational	O
resources	O
in	O
a	O
server	O
farm	O
-	O
typically	O
measured	O
by	O
the	O
number	O
of	O
active	O
servers	O
-	O
automatically	O
based	O
on	O
the	O
load	O
on	O
the	O
farm	O
.	O
</s>
<s>
Autoscaling	B-General_Concept
is	O
helpful	O
for	O
such	O
needs	O
,	O
as	O
it	O
can	O
reduce	O
the	O
number	O
of	O
active	O
servers	O
when	O
activity	O
is	O
low	O
,	O
and	O
launch	O
new	O
servers	O
when	O
activity	O
is	O
high	O
.	O
</s>
<s>
Autoscaling	B-General_Concept
is	O
closely	O
related	O
to	O
,	O
and	O
builds	O
upon	O
,	O
the	O
idea	O
of	O
load	B-Application
balancing	I-Application
.	O
</s>
<s>
Autoscaling	B-General_Concept
offers	O
the	O
following	O
advantages	O
:	O
</s>
<s>
For	O
companies	O
running	O
their	O
own	O
web	O
server	O
infrastructure	O
,	O
autoscaling	B-General_Concept
typically	O
means	O
allowing	O
some	O
servers	O
to	O
go	O
to	O
sleep	O
during	O
times	O
of	O
low	O
load	O
,	O
saving	O
on	O
electricity	O
costs	O
(	O
as	O
well	O
as	O
water	O
costs	O
if	O
water	O
is	O
being	O
used	O
to	O
cool	O
the	O
machines	O
)	O
.	O
</s>
<s>
For	O
companies	O
using	O
infrastructure	O
hosted	O
in	B-Architecture
the	I-Architecture
cloud	I-Architecture
,	O
autoscaling	B-General_Concept
can	O
mean	O
lower	O
bills	O
,	O
because	O
most	O
cloud	O
providers	O
charge	O
based	O
on	O
total	O
usage	O
rather	O
than	O
maximum	O
capacity	O
.	O
</s>
<s>
Even	O
for	O
companies	O
that	O
cannot	O
reduce	O
the	O
total	O
compute	O
capacity	O
they	O
run	O
or	O
pay	O
for	O
at	O
any	O
given	O
time	O
,	O
autoscaling	B-General_Concept
can	O
help	O
by	O
allowing	O
the	O
company	O
to	O
run	O
less	O
time-sensitive	O
workloads	O
on	O
machines	O
that	O
get	O
freed	O
up	O
by	O
autoscaling	B-General_Concept
during	O
times	O
of	O
low	O
traffic	O
.	O
</s>
<s>
Autoscaling	B-General_Concept
solutions	O
,	O
such	O
as	O
the	O
one	O
offered	O
by	O
Amazon	B-Application
Web	I-Application
Services	I-Application
,	O
can	O
also	O
take	O
care	O
of	O
replacing	O
unhealthy	O
instances	O
and	O
therefore	O
protecting	O
somewhat	O
against	O
hardware	O
,	O
network	O
,	O
and	O
application	O
failures	O
.	O
</s>
<s>
Autoscaling	B-General_Concept
can	O
offer	O
greater	O
uptime	O
and	O
more	O
availability	O
in	O
cases	O
where	O
production	O
workloads	O
are	O
variable	O
and	O
unpredictable	O
.	O
</s>
<s>
Autoscaling	B-General_Concept
differs	O
from	O
having	O
a	O
fixed	O
daily	O
,	O
weekly	O
,	O
or	O
yearly	O
cycle	O
of	O
server	O
use	O
in	O
that	O
it	O
is	O
responsive	O
to	O
actual	O
usage	O
patterns	O
,	O
and	O
thus	O
reduces	O
the	O
potential	O
downside	O
of	O
having	O
too	O
few	O
or	O
too	O
many	O
servers	O
for	O
the	O
traffic	O
load	O
.	O
</s>
<s>
Autoscaling	B-General_Concept
,	O
on	O
the	O
other	O
hand	O
,	O
can	O
handle	O
unexpected	O
traffic	O
spikes	O
better	O
.	O
</s>
<s>
In	O
the	O
list	O
below	O
,	O
we	O
use	O
the	O
terminology	O
used	O
by	O
Amazon	B-Application
Web	I-Application
Services	I-Application
(	O
AWS	B-Application
)	O
.	O
</s>
<s>
Name	O
(	O
used	O
in	O
AWS	B-Application
,	O
unless	O
otherwise	O
noted	O
)	O
Meaning	O
Alternative	O
names	O
(	O
used	O
in	O
Google	B-General_Concept
Cloud	I-General_Concept
Platform	I-General_Concept
,	O
Microsoft	B-Application
Azure	I-Application
,	O
or	O
other	O
platforms	O
)	O
Instance	O
A	O
single	O
server	O
or	O
machine	O
that	O
is	O
part	O
of	O
the	O
group	O
of	O
machines	O
subject	O
to	O
autoscaling	B-General_Concept
Autoscaling	B-General_Concept
group	O
The	O
collection	O
of	O
instances	O
subject	O
to	O
autoscaling	B-General_Concept
,	O
along	O
with	O
all	O
the	O
associated	O
policies	O
and	O
state	O
information	O
Managed	O
instance	O
group	O
(	O
Google	B-General_Concept
Cloud	I-General_Concept
Platform	I-General_Concept
)	O
Size	O
The	O
number	O
of	O
instances	O
currently	O
part	O
of	O
the	O
autoscaling	B-General_Concept
group	O
Desired	O
capacity	O
(	O
or	O
desired	O
size	O
)	O
The	O
number	O
of	O
instances	O
that	O
the	O
autoscaling	B-General_Concept
group	O
should	O
have	O
at	O
any	O
given	O
point	O
in	O
time	O
.	O
</s>
<s>
If	O
the	O
size	O
is	O
less	O
than	O
the	O
desired	O
size	O
,	O
the	O
autoscaling	B-General_Concept
group	O
will	O
try	O
to	O
launch	O
(	O
provision	O
and	O
attach	O
)	O
new	O
instances	O
.	O
</s>
<s>
If	O
the	O
size	O
is	O
more	O
than	O
the	O
desired	O
size	O
,	O
the	O
autoscaling	B-General_Concept
group	O
will	O
try	O
to	O
remove	O
(	O
detach	O
and	O
terminate	O
)	O
instances	O
Minimum	O
size	O
A	O
number	O
of	O
instances	O
below	O
which	O
the	O
desired	O
capacity	O
is	O
not	O
allowed	O
to	O
fall	O
Maximum	O
size	O
A	O
number	O
of	O
instances	O
above	O
which	O
the	O
desired	O
capacity	O
is	O
not	O
allowed	O
to	O
rise	O
Metric	O
A	O
measurement	O
(	O
such	O
as	O
CPU	O
utilization	O
,	O
memory	O
usage	O
,	O
network	O
usage	O
)	O
associated	O
with	O
the	O
autoscaling	B-General_Concept
group	O
,	O
for	O
which	O
a	O
time	O
series	O
of	O
data	O
points	O
is	O
generated	O
regularly	O
.	O
</s>
<s>
Thresholds	O
for	O
metrics	O
can	O
be	O
used	O
to	O
set	O
autoscaling	B-General_Concept
policies	O
.	O
</s>
<s>
Metrics	O
can	O
be	O
based	O
on	O
aggregates	O
of	O
metrics	O
for	O
instances	O
of	O
the	O
autoscaling	B-General_Concept
group	O
,	O
or	O
based	O
on	O
load	B-Application
balancers	I-Application
associated	O
with	O
the	O
autoscaling	B-General_Concept
group	O
Scaling	O
policy	O
(	O
or	O
autoscaling	B-General_Concept
policy	O
)	O
A	O
policy	O
that	O
specifies	O
a	O
change	O
to	O
the	O
autoscaling	B-General_Concept
group	O
's	O
desired	O
capacity	O
(	O
or	O
sometimes	O
,	O
its	O
minimum	O
and	O
maximum	O
size	O
)	O
in	O
response	O
to	O
metrics	O
crossing	O
specific	O
thresholds	O
.	O
</s>
<s>
Policies	O
that	O
increase	O
the	O
desired	O
capacity	O
are	O
called	O
"	O
scaling	O
out	O
"	O
or	O
"	O
scaling	O
up	O
"	O
policies	O
,	O
and	O
policies	O
that	O
decrease	O
the	O
desired	O
capacity	O
are	O
called	O
"	O
scaling	O
in	O
"	O
or	O
"	O
scaling	O
down	O
"	O
policies	O
Health	O
check	O
A	O
way	O
for	O
the	O
autoscaling	B-General_Concept
group	O
to	O
determine	O
if	O
the	O
instances	O
attached	O
to	O
it	O
are	O
functioning	O
properly	O
.	O
</s>
<s>
A	O
health	O
check	O
may	O
be	O
based	O
on	O
whether	O
the	O
instance	O
still	O
exists	O
and	O
is	O
reachable	O
,	O
or	O
it	O
could	O
be	O
based	O
on	O
whether	O
the	O
instance	O
is	O
still	O
registered	O
and	O
in	O
service	O
with	O
an	O
associated	O
load	B-Application
balancer	I-Application
Launch	O
configuration	O
A	O
description	O
of	O
the	O
parameters	O
and	O
scripts	O
used	O
when	O
launching	O
a	O
new	O
instance	O
.	O
</s>
<s>
This	O
includes	O
the	O
instance	O
type	O
,	O
purchase	O
options	O
(	O
such	O
as	O
spot	O
versus	O
on-demand	O
in	O
the	O
case	O
of	O
AWS	B-Application
)	O
,	O
possible	O
availability	O
zones	O
for	O
launch	O
,	O
machine	O
image	O
,	O
and	O
scripts	O
to	O
run	O
on	O
launch	O
Instance	O
template	O
(	O
Google	B-General_Concept
Cloud	I-General_Concept
Platform	I-General_Concept
)	O
Manual	O
scaling	O
A	O
scaling	O
action	O
executed	O
manually	O
Scheduled	O
scaling	O
A	O
scaling	O
policy	O
that	O
is	O
executed	O
at	O
a	O
specific	O
time	O
,	O
for	O
instance	O
,	O
time	O
of	O
day	O
or	O
week	O
or	O
month	O
or	O
year	O
.	O
</s>
<s>
Amazon	B-Application
Web	I-Application
Services	I-Application
launched	O
the	O
Amazon	B-General_Concept
Elastic	I-General_Concept
Compute	I-General_Concept
Cloud	I-General_Concept
(	O
EC2	O
)	O
service	O
in	O
August	O
2006	O
,	O
that	O
allowed	O
developers	O
to	O
programmatically	O
create	O
and	O
terminate	O
instances	O
(	O
machines	O
)	O
.	O
</s>
<s>
At	O
the	O
time	O
of	O
initial	O
launch	O
,	O
AWS	B-Application
did	O
not	O
offer	O
autoscaling	B-General_Concept
,	O
but	O
the	O
ability	O
to	O
programmatically	O
create	O
and	O
terminate	O
instances	O
gave	O
developers	O
the	O
flexibility	O
to	O
write	O
their	O
own	O
code	O
for	O
autoscaling	B-General_Concept
.	O
</s>
<s>
Third-party	O
autoscaling	B-General_Concept
software	O
for	O
AWS	B-Application
began	O
appearing	O
around	O
April	O
2008	O
.	O
</s>
<s>
RightScale	O
was	O
used	O
by	O
Animoto	O
,	O
which	O
was	O
able	O
to	O
handle	O
Facebook	O
traffic	O
by	O
adopting	O
autoscaling	B-General_Concept
.	O
</s>
<s>
On	O
May	O
18	O
,	O
2009	O
,	O
Amazon	O
launched	O
its	O
own	O
autoscaling	B-General_Concept
feature	O
along	O
with	O
Elastic	B-General_Concept
Load	I-General_Concept
Balancing	I-General_Concept
,	O
as	O
part	O
of	O
Amazon	B-General_Concept
Elastic	I-General_Concept
Compute	I-General_Concept
Cloud	I-General_Concept
.	O
</s>
<s>
Autoscaling	B-General_Concept
is	O
now	O
an	O
integral	O
component	O
of	O
Amazon	O
's	O
EC2	O
offering	O
.	O
</s>
<s>
Autoscaling	B-General_Concept
on	O
Amazon	B-Application
Web	I-Application
Services	I-Application
is	O
done	O
through	O
a	O
web	O
browser	O
or	O
the	O
command	O
line	O
tool	O
.	O
</s>
<s>
In	O
May	O
2016	O
Autoscaling	B-General_Concept
was	O
also	O
offered	O
in	O
AWS	B-Application
ECS	O
Service	O
.	O
</s>
<s>
On-demand	O
video	O
provider	O
Netflix	O
documented	O
their	O
use	O
of	O
autoscaling	B-General_Concept
with	O
Amazon	B-Application
Web	I-Application
Services	I-Application
to	O
meet	O
their	O
highly	O
variable	O
consumer	O
needs	O
.	O
</s>
<s>
In	O
an	O
article	O
for	O
TechCrunch	O
,	O
Zev	O
Laderman	O
,	O
the	O
co-founder	O
and	O
CEO	O
of	O
Newvem	O
,	O
a	O
service	O
that	O
helps	O
optimize	O
AWS	B-Application
cloud	O
infrastructure	O
,	O
recommended	O
that	O
startups	O
use	O
autoscaling	B-General_Concept
in	O
order	O
to	O
keep	O
their	O
Amazon	B-Application
Web	I-Application
Services	I-Application
costs	O
low	O
.	O
</s>
<s>
Various	O
best	O
practice	O
guides	O
for	O
AWS	B-Application
use	O
suggest	O
using	O
its	O
autoscaling	B-General_Concept
feature	O
even	O
in	O
cases	O
where	O
the	O
load	O
is	O
not	O
variable	O
.	O
</s>
<s>
That	O
is	O
because	O
autoscaling	B-General_Concept
offers	O
two	O
other	O
advantages	O
:	O
automatic	O
replacement	O
of	O
any	O
instances	O
that	O
become	O
unhealthy	O
for	O
any	O
reason	O
(	O
such	O
as	O
hardware	O
failure	O
,	O
network	O
failure	O
,	O
or	O
application	O
error	O
)	O
,	O
and	O
automatic	O
replacement	O
of	O
spot	O
instances	O
that	O
get	O
interrupted	O
for	O
price	O
or	O
capacity	O
reasons	O
,	O
making	O
it	O
more	O
feasible	O
to	O
use	O
spot	O
instances	O
for	O
production	O
purposes	O
.	O
</s>
<s>
Netflix	O
's	O
internal	O
best	O
practices	O
require	O
every	O
instance	O
to	O
be	O
in	O
an	O
autoscaling	B-General_Concept
group	O
,	O
and	O
its	O
conformity	O
monkey	O
terminates	O
any	O
instance	O
not	O
in	O
an	O
autoscaling	B-General_Concept
group	O
in	O
order	O
to	O
enforce	O
this	O
best	O
practice	O
.	O
</s>
<s>
On	O
June	O
27	O
,	O
2013	O
,	O
Microsoft	O
announced	O
that	O
it	O
was	O
adding	O
autoscaling	B-General_Concept
support	O
to	O
its	O
Windows	B-Application
Azure	I-Application
cloud	B-Architecture
computing	I-Architecture
platform	I-Architecture
.	O
</s>
<s>
Oracle	O
Cloud	O
Platform	O
allows	O
server	O
instances	O
to	O
automatically	O
scale	O
a	O
cluster	O
in	O
or	O
out	O
by	O
defining	O
an	O
auto-scaling	B-General_Concept
rule	O
.	O
</s>
<s>
On	O
November	O
17	O
,	O
2014	O
,	O
the	O
Google	B-General_Concept
Compute	I-General_Concept
Engine	I-General_Concept
announced	O
a	O
public	O
beta	O
of	O
its	O
autoscaling	B-General_Concept
feature	O
for	O
use	O
in	O
Google	B-General_Concept
Cloud	I-General_Concept
Platform	I-General_Concept
applications	O
.	O
</s>
<s>
As	O
of	O
March	O
2015	O
,	O
the	O
autoscaling	B-General_Concept
tool	O
is	O
still	O
in	O
Beta	O
.	O
</s>
<s>
In	O
a	O
blog	O
post	O
in	O
August	O
2014	O
,	O
a	O
Facebook	O
engineer	O
disclosed	O
that	O
the	O
company	O
had	O
started	O
using	O
autoscaling	B-General_Concept
to	O
bring	O
down	O
its	O
energy	O
costs	O
.	O
</s>
<s>
Autoscaling	B-General_Concept
by	O
default	O
uses	O
reactive	O
decision	O
approach	O
for	O
dealing	O
with	O
traffic	O
scaling	O
:	O
scaling	O
only	O
happens	O
in	O
response	O
to	O
real-time	O
changes	O
in	O
metrics	O
.	O
</s>
<s>
Two	O
other	O
kinds	O
of	O
autoscaling	B-General_Concept
decision	O
approaches	O
are	O
described	O
below	O
.	O
</s>
<s>
This	O
is	O
an	O
approach	O
to	O
autoscaling	B-General_Concept
where	O
changes	O
are	O
made	O
to	O
the	O
minimum	O
size	O
,	O
maximum	O
size	O
,	O
or	O
desired	O
capacity	O
of	O
the	O
autoscaling	B-General_Concept
group	O
at	O
specific	O
times	O
of	O
day	O
.	O
</s>
<s>
Scheduled	O
scaling	O
is	O
useful	O
,	O
for	O
instance	O
,	O
if	O
there	O
is	O
a	O
known	O
traffic	O
load	O
increase	O
or	O
decrease	O
at	O
specific	O
times	O
of	O
the	O
day	O
,	O
but	O
the	O
change	O
is	O
too	O
sudden	O
for	O
reactive	O
approach	O
based	O
autoscaling	B-General_Concept
to	O
respond	O
fast	O
enough	O
.	O
</s>
<s>
AWS	B-Application
autoscaling	B-General_Concept
groups	O
support	O
scheduled	O
scaling	O
.	O
</s>
<s>
This	O
approach	O
to	O
autoscaling	B-General_Concept
uses	O
predictive	B-General_Concept
analytics	I-General_Concept
.	O
</s>
<s>
For	O
parts	O
of	O
their	O
infrastructure	O
and	O
specific	O
workloads	O
,	O
Netflix	O
found	O
that	O
Scryer	O
,	O
their	O
predictive	B-General_Concept
analytics	I-General_Concept
engine	O
,	O
gave	O
better	O
results	O
than	O
Amazon	O
's	O
reactive	O
autoscaling	B-General_Concept
approach	O
.	O
</s>
<s>
On	O
November	O
20	O
,	O
2018	O
,	O
AWS	B-Application
announced	O
that	O
predictive	O
scaling	O
would	O
be	O
available	O
as	O
part	O
of	O
its	O
autoscaling	B-General_Concept
offering	O
.	O
</s>
