<s>
Container	B-Application
Linux	I-Application
(	O
formerly	O
CoreOS	B-Application
Linux	B-Application
)	O
is	O
a	O
discontinued	O
open-source	B-Application
lightweight	O
operating	B-General_Concept
system	I-General_Concept
based	O
on	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
and	O
designed	O
for	O
providing	O
infrastructure	O
to	O
clustered	B-Architecture
deployments	O
,	O
while	O
focusing	O
on	O
automation	O
,	O
ease	O
of	O
application	O
deployment	O
,	O
security	O
,	O
reliability	O
and	O
scalability	B-Architecture
.	O
</s>
<s>
As	O
an	O
operating	B-General_Concept
system	I-General_Concept
,	O
Container	B-Application
Linux	I-Application
provided	O
only	O
the	O
minimal	O
functionality	O
required	O
for	O
deploying	O
applications	O
inside	O
software	B-Application
containers	I-Application
,	O
together	O
with	O
built-in	O
mechanisms	O
for	O
service	B-Protocol
discovery	I-Protocol
and	O
configuration	O
sharing	O
.	O
</s>
<s>
Container	B-Application
Linux	I-Application
shares	O
foundations	O
with	O
Gentoo	B-Application
Linux	I-Application
,	O
ChromeOS	B-Operating_System
,	O
and	O
ChromiumOS	B-Application
through	O
a	O
common	O
software	B-Application
development	I-Application
kit	I-Application
(	O
SDK	O
)	O
.	O
</s>
<s>
Container	B-Application
Linux	I-Application
adds	O
new	O
functionality	O
and	O
customization	O
to	O
this	O
shared	O
foundation	O
to	O
support	O
server	O
hardware	O
and	O
use	O
cases	O
.	O
</s>
<s>
CoreOS	B-Application
was	O
developed	O
primarily	O
by	O
Alex	O
Polvi	O
,	O
Brandon	O
Philips	O
and	O
Michael	O
Marineau	O
,	O
with	O
its	O
major	O
features	O
available	O
as	O
a	O
stable	O
release	O
.	O
</s>
<s>
The	O
CoreOS	B-Application
team	O
announced	O
the	O
end-of-life	O
for	O
Container	B-Application
Linux	I-Application
on	O
May	O
26	O
,	O
2020	O
,	O
offering	O
Fedora	O
CoreOS	B-Application
,	O
and	O
RHEL	O
CoreOS	B-Application
as	O
its	O
replacement	O
,	O
both	O
based	O
on	O
Red	O
Hat	O
.	O
</s>
<s>
Container	B-Application
Linux	I-Application
provides	O
no	O
package	B-Application
manager	I-Application
as	O
a	O
way	O
for	O
distributing	O
payload	O
applications	O
,	O
requiring	O
instead	O
all	O
applications	O
to	O
run	O
inside	O
their	O
containers	B-Application
.	O
</s>
<s>
Serving	O
as	O
a	O
single	O
control	O
host	O
,	O
a	O
Container	B-Application
Linux	I-Application
instance	O
uses	O
the	O
underlying	O
operating-system-level	B-Application
virtualization	I-Application
features	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
to	O
create	O
and	O
configure	O
multiple	O
containers	B-Application
that	O
perform	O
as	O
isolated	O
Linux	B-Application
systems	O
.	O
</s>
<s>
That	O
way	O
,	O
resource	B-General_Concept
partitioning	B-Application
between	O
containers	B-Application
is	O
performed	O
through	O
multiple	O
isolated	O
userspace	B-Operating_System
instances	O
,	O
instead	O
of	O
using	O
a	O
hypervisor	B-Operating_System
and	O
providing	O
full-fledged	O
virtual	B-Architecture
machines	I-Architecture
.	O
</s>
<s>
This	O
approach	O
relies	O
on	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
's	O
cgroups	B-Application
and	O
namespaces	B-Architecture
functionalities	O
,	O
which	O
together	O
provide	O
abilities	O
to	O
limit	O
,	O
account	O
and	O
isolate	O
resource	B-General_Concept
usage	O
(	O
CPU	B-Device
,	O
memory	O
,	O
disk	O
I/O	B-General_Concept
,	O
etc	O
.	O
)	O
</s>
<s>
for	O
the	O
collections	O
of	O
userspace	B-Operating_System
processes	B-Operating_System
.	O
</s>
<s>
Initially	O
,	O
Container	B-Application
Linux	I-Application
exclusively	O
used	O
Docker	B-Language
as	O
a	O
component	O
providing	O
an	O
additional	O
layer	O
of	O
abstraction	O
and	O
interface	B-Application
to	O
the	O
operating-system-level	B-Application
virtualization	I-Application
features	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
,	O
as	O
well	O
as	O
providing	O
a	O
standardized	O
format	O
for	O
containers	B-Application
that	O
allows	O
applications	O
to	O
run	O
in	O
different	O
environments	O
.	O
</s>
<s>
In	O
December	O
2014	O
,	O
CoreOS	B-Application
released	O
and	O
started	O
to	O
support	O
rkt	O
(	O
initially	O
released	O
as	O
Rocket	O
)	O
as	O
an	O
alternative	O
to	O
Docker	B-Language
,	O
providing	O
through	O
it	O
another	O
standardized	O
format	O
of	O
the	O
application-container	O
images	O
,	O
the	O
related	O
definition	O
of	O
the	O
container	B-Application
runtime	B-Device
environment	I-Device
,	O
and	O
a	O
protocol	O
for	O
discovering	O
and	O
retrieving	O
container	B-Application
images	O
.	O
</s>
<s>
CoreOS	B-Application
provides	O
rkt	O
as	O
an	O
implementation	O
of	O
the	O
so-called	O
app	O
container	B-Application
(	O
appc	O
)	O
specification	O
that	O
describes	O
required	O
properties	O
of	O
the	O
application	O
container	B-Application
image	O
(	O
ACI	O
)	O
.	O
</s>
<s>
Container	B-Application
Linux	I-Application
uses	O
ebuild	O
scripts	O
from	O
Gentoo	B-Application
Linux	I-Application
for	O
automated	O
compilation	B-Language
of	O
its	O
system	O
components	O
,	O
and	O
uses	O
systemd	B-Application
as	O
its	O
primary	O
init	B-Operating_System
system	I-Operating_System
with	O
tight	O
integration	O
between	O
systemd	B-Application
and	O
various	O
Container	B-Application
Linux	I-Application
's	O
internal	O
mechanisms	O
.	O
</s>
<s>
Container	B-Application
Linux	I-Application
achieves	O
additional	O
security	O
and	O
reliability	O
of	O
its	O
operating	B-General_Concept
system	I-General_Concept
updates	O
by	O
employing	O
FastPatch	O
as	O
a	O
dual-partition	O
scheme	O
for	O
the	O
read-only	O
part	O
of	O
its	O
installation	O
,	O
meaning	O
that	O
the	O
updates	O
are	O
performed	O
as	O
a	O
whole	O
and	O
installed	O
onto	O
a	O
passive	O
secondary	O
boot	O
partition	B-Application
that	O
becomes	O
active	O
upon	O
a	O
reboot	B-Device
or	O
kexec	B-Application
.	O
</s>
<s>
This	O
approach	O
avoids	O
possible	O
issues	O
arising	O
from	O
updating	O
only	O
certain	O
parts	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
ensures	O
easy	O
rollbacks	O
to	O
a	O
known-to-be-stable	O
version	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
and	O
allows	O
each	O
boot	O
partition	B-Application
to	O
be	O
signed	O
for	O
additional	O
security	O
.	O
</s>
<s>
The	O
root	O
partition	B-Application
and	O
its	O
root	B-Application
file	I-Application
system	I-Application
are	O
automatically	O
resized	O
to	O
fill	O
all	O
available	O
disk-space	O
upon	O
reboots	B-Device
;	O
while	O
the	O
root	O
partition	B-Application
provides	O
read-write	O
storage	O
space	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
itself	O
is	O
mounted	B-Application
read-only	O
under	O
.	O
</s>
<s>
To	O
ensure	O
that	O
only	O
a	O
certain	O
part	O
of	O
the	O
cluster	B-Architecture
reboots	B-Device
at	O
once	O
when	O
the	O
operating	B-General_Concept
system	I-General_Concept
updates	O
are	O
applied	O
,	O
preserving	O
that	O
way	O
the	O
resources	O
required	O
for	O
running	O
deployed	O
applications	O
,	O
CoreOS	B-Application
provides	O
locksmith	O
as	O
a	O
reboot	B-Device
manager	O
for	O
Container	B-Application
Linux	I-Application
.	O
</s>
<s>
Using	O
locksmith	O
,	O
one	O
can	O
select	O
between	O
different	O
update	O
strategies	O
that	O
are	O
determined	O
by	O
how	O
the	O
reboots	B-Device
are	O
performed	O
as	O
the	O
last	O
step	O
in	O
applying	O
updates	O
;	O
for	O
example	O
,	O
one	O
can	O
configure	O
how	O
many	O
cluster	B-Architecture
members	O
are	O
allowed	O
to	O
reboot	B-Device
simultaneously	O
.	O
</s>
<s>
Internally	O
,	O
locksmith	O
operates	O
as	O
the	O
daemon	B-Operating_System
that	O
runs	O
on	O
cluster	B-Architecture
members	O
,	O
while	O
the	O
command-line	B-Application
utility	O
manages	O
configuration	O
parameters	O
.	O
</s>
<s>
Locksmith	O
is	O
written	O
in	O
the	O
Go	B-Application
language	I-Application
and	O
distributed	B-Architecture
under	O
the	O
terms	O
of	O
the	O
Apache	B-Application
License	I-Application
2.0	I-Application
.	O
</s>
<s>
The	O
updates	O
distribution	O
system	O
employed	O
by	O
Container	B-Application
Linux	I-Application
is	O
based	O
on	O
Google	B-Application
's	I-Application
open-source	B-Application
Omaha	O
project	O
,	O
which	O
provides	O
a	O
mechanism	O
for	O
rolling	O
out	O
updates	O
and	O
the	O
underlying	O
request	B-Protocol
–	I-Protocol
response	I-Protocol
protocol	O
based	O
on	O
XML	B-Protocol
.	O
</s>
<s>
Additionally	O
,	O
CoreOS	B-Application
provides	O
CoreUpdate	O
as	O
a	O
web-based	O
dashboard	B-Protocol
for	O
the	O
management	O
of	O
cluster-wide	O
updates	O
.	O
</s>
<s>
Operations	O
available	O
through	O
CoreUpdate	O
include	O
assigning	O
cluster	B-Architecture
members	O
to	O
different	O
groups	O
that	O
share	O
customized	O
update	O
policies	O
,	O
reviewing	O
cluster-wide	O
breakdowns	O
of	O
Container	B-Application
Linux	I-Application
versions	O
,	O
stopping	O
and	O
restarting	O
updates	O
,	O
and	O
reviewing	O
recorded	O
update	O
logs	O
.	O
</s>
<s>
CoreUpdate	O
also	O
provides	O
a	O
HTTP-based	O
API	B-General_Concept
that	O
allows	O
its	O
integration	O
into	O
third-party	O
utilities	O
or	O
deployment	O
systems	O
.	O
</s>
<s>
Container	B-Application
Linux	I-Application
provides	O
etcd	O
,	O
a	O
daemon	B-Operating_System
that	O
runs	O
across	O
all	O
computers	O
in	O
a	O
cluster	B-Architecture
and	O
provides	O
a	O
dynamic	O
configuration	O
registry	O
,	O
allowing	O
various	O
configuration	O
data	O
to	O
be	O
easily	O
and	O
reliably	O
shared	O
between	O
the	O
cluster	B-Architecture
members	O
.	O
</s>
<s>
Since	O
the	O
key	B-Application
–	I-Application
value	I-Application
data	I-Application
stored	O
within	O
is	O
automatically	O
distributed	B-Architecture
and	O
replicated	B-Architecture
with	O
automated	O
master	O
election	O
and	O
consensus	B-Operating_System
establishment	O
using	O
the	O
Raft	B-Operating_System
algorithm	O
,	O
all	O
changes	O
in	O
stored	O
data	O
are	O
reflected	O
across	O
the	O
entire	O
cluster	B-Architecture
,	O
while	O
the	O
achieved	O
redundancy	O
prevents	O
failures	O
of	O
single	O
cluster	B-Architecture
members	O
from	O
causing	O
data	O
loss	O
.	O
</s>
<s>
Beside	O
the	O
configuration	O
management	O
,	O
also	O
provides	O
service	B-Protocol
discovery	I-Protocol
by	O
allowing	O
deployed	O
applications	O
to	O
announce	O
themselves	O
and	O
the	O
services	O
they	O
offer	O
.	O
</s>
<s>
Communication	O
with	O
is	O
performed	O
through	O
an	O
exposed	O
REST-based	O
API	B-General_Concept
,	O
which	O
internally	O
uses	O
JSON	B-General_Concept
on	O
top	O
of	O
HTTP	B-Protocol
;	I-Protocol
the	O
API	B-General_Concept
may	O
be	O
used	O
directly	O
(	O
through	O
or	O
,	O
for	O
example	O
)	O
,	O
or	O
indirectly	O
through	O
,	O
which	O
is	O
a	O
specialized	O
command-line	B-Application
utility	O
also	O
supplied	O
by	O
CoreOS	B-Application
.	O
</s>
<s>
Etcd	O
is	O
also	O
used	O
in	O
Kubernetes	B-General_Concept
software	O
.	O
</s>
<s>
Container	B-Application
Linux	I-Application
also	O
provides	O
the	O
cluster	B-Architecture
manager	O
which	O
controls	O
Container	B-Application
Linux	I-Application
's	O
separate	O
systemd	B-Application
instances	O
at	O
the	O
cluster	B-Architecture
level	O
.	O
</s>
<s>
As	O
of	O
2017	O
"	O
fleet	O
"	O
is	O
no	O
longer	O
actively	O
developed	O
and	O
is	O
deprecated	O
in	O
favor	O
of	O
Kubernetes	B-General_Concept
.	O
</s>
<s>
By	O
using	O
,	O
Container	B-Application
Linux	I-Application
creates	O
a	O
distributed	B-Architecture
init	B-Operating_System
system	I-Operating_System
that	O
ties	O
together	O
separate	O
systemd	B-Application
instances	O
and	O
a	O
cluster-wide	O
deployment	O
;	O
internally	O
,	O
daemon	B-Operating_System
communicates	O
with	O
local	O
instances	O
over	O
D-Bus	B-Language
,	O
and	O
with	O
the	O
deployment	O
through	O
its	O
exposed	O
API	B-General_Concept
.	O
</s>
<s>
Using	O
allows	O
the	O
deployment	O
of	O
single	O
or	O
multiple	O
containers	B-Application
cluster-wide	O
,	O
with	O
more	O
advanced	O
options	O
including	O
redundancy	O
,	O
failover	B-General_Concept
,	O
deployment	O
to	O
specific	O
cluster	B-Architecture
members	O
,	O
dependencies	O
between	O
containers	B-Application
,	O
and	O
grouped	O
deployment	O
of	O
containers	B-Application
.	O
</s>
<s>
A	O
command-line	B-Application
utility	O
called	O
is	O
used	O
to	O
configure	O
and	O
monitor	O
this	O
distributed	B-Architecture
init	B-Operating_System
system	I-Operating_System
;	O
internally	O
,	O
it	O
communicates	O
with	O
the	O
daemon	B-Operating_System
using	O
a	O
JSON-based	O
API	B-General_Concept
on	O
top	O
of	O
HTTP	B-Protocol
,	O
which	O
may	O
also	O
be	O
used	O
directly	O
.	O
</s>
<s>
When	O
used	O
locally	O
on	O
a	O
cluster	B-Architecture
member	O
,	O
communicates	O
with	O
the	O
local	O
instance	O
over	O
a	O
Unix	B-Protocol
domain	I-Protocol
socket	I-Protocol
;	O
when	O
used	O
from	O
an	O
external	O
host	O
,	O
SSH	B-Protocol
tunneling	O
is	O
used	O
with	O
authentication	O
provided	O
through	O
public	B-Protocol
SSH	I-Protocol
keys	I-Protocol
.	O
</s>
<s>
All	O
of	O
the	O
above-mentioned	O
daemons	B-Operating_System
and	O
command-line	B-Application
utilities	O
(	O
,	O
,	O
and	O
)	O
are	O
written	O
in	O
the	O
Go	B-Application
language	I-Application
and	O
distributed	B-Architecture
under	O
the	O
terms	O
of	O
the	O
Apache	B-Application
License	I-Application
2.0	I-Application
.	O
</s>
<s>
When	O
running	O
on	O
dedicated	O
hardware	O
,	O
Container	B-Application
Linux	I-Application
can	O
be	O
either	O
permanently	O
installed	O
to	O
local	O
storage	O
,	O
such	O
as	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
(	O
HDD	O
)	O
or	O
solid-state	B-Device
drive	I-Device
(	O
SSD	B-Device
)	O
,	O
or	O
booted	O
remotely	O
over	B-Device
a	I-Device
network	I-Device
using	O
Preboot	B-Device
Execution	I-Device
Environment	I-Device
(	O
PXE	O
)	O
in	O
general	O
,	O
or	O
iPXE	B-Device
as	O
one	O
of	O
its	O
implementations	O
.	O
</s>
<s>
CoreOS	B-Application
also	O
supports	O
deployments	O
on	O
various	O
hardware	B-General_Concept
virtualization	I-General_Concept
platforms	O
,	O
including	O
Amazon	B-General_Concept
EC2	I-General_Concept
,	O
DigitalOcean	B-Application
,	O
Google	B-General_Concept
Compute	I-General_Concept
Engine	I-General_Concept
,	O
Microsoft	B-Application
Azure	I-Application
,	O
OpenStack	B-Application
,	O
QEMU/KVM	O
,	O
Vagrant	B-Application
and	O
VMware	O
.	O
</s>
<s>
Container	B-Application
Linux	I-Application
may	O
also	O
be	O
installed	O
on	O
Citrix	O
XenServer	O
,	O
noting	O
that	O
a	O
"	O
template	O
"	O
for	O
CoreOS	B-Application
exists	O
.	O
</s>
<s>
Container	B-Application
Linux	I-Application
can	O
also	O
be	O
deployed	O
through	O
its	O
commercial	O
distribution	O
called	O
Tectonic	O
,	O
which	O
additionally	O
integrates	O
Google	B-Application
's	I-Application
Kubernetes	B-General_Concept
as	O
a	O
cluster	B-Architecture
management	O
utility	O
.	O
</s>
<s>
Furthermore	O
,	O
CoreOS	B-Application
provides	O
Flannel	O
as	O
a	O
component	O
implementing	O
an	O
overlay	B-Architecture
network	I-Architecture
required	O
primarily	O
for	O
the	O
integration	O
with	O
Kubernetes	B-General_Concept
.	O
</s>
<s>
,	O
Container	B-Application
Linux	I-Application
supports	O
only	O
the	O
x86-64	B-Device
architecture	O
.	O
</s>
<s>
Following	O
its	O
acquisition	O
of	O
CoreOS	B-Application
,	O
Inc	O
.	O
in	O
January	O
2018	O
,	O
Red	O
Hat	O
announced	O
that	O
it	O
would	O
be	O
merging	O
CoreOS	B-Application
Container	B-Application
Linux	I-Application
with	O
Red	O
Hat	O
's	O
Project	O
Atomic	O
,	O
to	O
create	O
a	O
new	O
operating	B-General_Concept
system	I-General_Concept
,	O
Red	O
Hat	O
CoreOS	B-Application
,	O
while	O
aligning	O
the	O
upstream	O
Fedora	O
Project	O
open	B-Application
source	I-Application
community	O
around	O
Fedora	O
CoreOS	B-Application
,	O
combining	O
technologies	O
from	O
both	O
predecessors	O
.	O
</s>
<s>
On	O
March	O
6	O
,	O
2018	O
,	O
Kinvolk	O
GmbH	O
announced	O
,	O
a	O
derivative	O
of	O
CoreOS	B-Application
Container	B-Application
Linux	I-Application
.	O
</s>
<s>
This	O
tracks	O
the	O
upstream	O
CoreOS	B-Application
alpha/beta/stable	O
channel	O
releases	O
,	O
with	O
an	O
experimental	O
Edge	O
release	O
channel	O
added	O
in	O
May	O
2019	O
.	O
</s>
<s>
LWN.net	O
reviewed	O
CoreOS	B-Application
in	O
2014	O
:	O
</s>
