<s>
Ganglia	B-Language
is	O
a	O
scalable	O
,	O
distributed	O
monitoring	B-Application
tool	O
for	O
high-performance	O
computing	O
systems	O
,	O
clusters	O
and	O
networks	O
.	O
</s>
<s>
The	O
software	O
is	O
used	O
to	O
view	O
either	O
live	O
or	O
recorded	O
statistics	O
covering	O
metrics	O
such	O
as	O
CPU	B-General_Concept
load	O
averages	O
or	O
network	O
utilization	O
for	O
many	O
nodes	O
.	O
</s>
<s>
Ganglia	B-Language
software	I-Language
is	O
bundled	O
with	O
enterprise-level	O
Linux	B-Application
distributions	O
such	O
as	O
Red	O
Hat	O
Enterprise	O
Level	O
(	O
RHEL	O
)	O
or	O
the	O
CentOS	O
repackaging	O
of	O
the	O
same	O
.	O
</s>
<s>
Ganglia	B-Language
grew	O
out	O
of	O
requirements	O
for	O
monitoring	B-Application
systems	O
by	O
Berkeley	O
(	O
University	O
of	O
California	O
)	O
but	O
now	O
sees	O
use	O
by	O
commercial	O
and	O
educational	O
organisations	O
such	O
as	O
Cray	O
,	O
MIT	O
,	O
NASA	O
and	O
Twitter	O
.	O
</s>
<s>
It	O
leverages	O
widely	O
used	O
technologies	O
such	O
as	O
XML	B-Protocol
for	O
data	O
representation	O
,	O
XDR	B-Protocol
for	O
compact	O
,	O
portable	O
data	O
transport	O
,	O
and	O
RRDtool	B-Language
for	O
data	O
storage	O
and	O
visualization	O
.	O
</s>
<s>
The	O
ganglia	B-Language
system	O
comprises	O
two	O
unique	O
daemons	O
,	O
a	O
PHP-based	O
web	O
front-end	O
,	O
and	O
a	O
few	O
other	O
small	O
utility	O
programs	O
.	O
</s>
<s>
Installation	O
does	O
not	O
require	O
having	O
a	O
common	O
NFS	B-Protocol
filesystem	I-Protocol
or	O
a	O
database	O
back-end	O
,	O
installing	O
special	O
accounts	O
or	O
maintaining	O
configuration	O
files	O
.	O
</s>
<s>
Listen	O
to	O
the	O
state	O
of	O
all	O
other	O
ganglia	B-Language
nodes	O
via	O
a	O
unicast	B-Protocol
or	O
multicast	O
channel	O
.	O
</s>
<s>
Answer	O
requests	O
for	O
an	O
XML	B-Protocol
description	O
of	O
the	O
cluster	O
state	O
.	O
</s>
<s>
Unicasting	B-Protocol
or	O
Multicasting	O
host	O
state	O
in	O
external	B-Protocol
data	I-Protocol
representation	I-Protocol
(	O
XDR	B-Protocol
)	O
format	O
using	O
UDP	B-Protocol
messages	O
.	O
</s>
<s>
Sending	O
XML	B-Protocol
over	O
a	O
TCP	B-Protocol
connection	O
.	O
</s>
<s>
Federation	O
in	O
Ganglia	B-Language
is	O
achieved	O
using	O
a	O
tree	O
of	O
point-to-point	O
connections	O
amongst	O
representative	O
cluster	O
nodes	O
to	O
aggregate	O
the	O
state	O
of	O
multiple	O
clusters	O
.	O
</s>
<s>
At	O
each	O
node	O
in	O
the	O
tree	O
,	O
a	O
Ganglia	B-Language
Meta	O
Daemon	O
(	O
gmetad	O
)	O
periodically	O
polls	O
a	O
collection	O
of	O
child	O
data	O
sources	O
,	O
parses	O
the	O
collected	O
XML	B-Protocol
,	O
saves	O
all	O
numeric	O
,	O
volatile	O
metrics	O
to	O
round-robin	B-Language
databases	I-Language
and	O
exports	O
the	O
aggregated	O
XML	B-Protocol
over	O
a	O
TCP	B-Protocol
socket	O
to	O
clients	O
.	O
</s>
<s>
Data	O
sources	O
use	O
source	O
IP	B-Protocol
addresses	I-Protocol
for	O
access	O
control	O
and	O
can	O
be	O
specified	O
using	O
multiple	O
IP	B-Protocol
addresses	I-Protocol
for	O
failover	O
.	O
</s>
<s>
The	O
Ganglia	B-Language
web	O
front-end	O
provides	O
a	O
view	O
of	O
the	O
gathered	O
information	O
via	O
real-time	O
dynamic	O
web	O
pages	O
.	O
</s>
<s>
Most	O
importantly	O
,	O
it	O
displays	O
Ganglia	B-Language
data	O
in	O
a	O
meaningful	O
way	O
for	O
system	B-Application
administrators	I-Application
and	O
computer	O
users	O
.	O
</s>
<s>
Although	O
the	O
web	O
front-end	O
to	O
ganglia	B-Language
started	O
as	O
a	O
simple	O
HTML	B-Language
view	O
of	O
the	O
XML	B-Protocol
tree	O
,	O
it	O
has	O
evolved	O
into	O
a	O
system	O
that	O
keeps	O
a	O
colorful	O
history	O
of	O
all	O
collected	O
data	O
.	O
</s>
<s>
The	O
Ganglia	B-Language
web	O
front-end	O
caters	O
to	O
system	B-Application
administrators	I-Application
and	O
users	O
.	O
</s>
<s>
For	O
example	O
,	O
one	O
can	O
view	O
the	O
CPU	B-General_Concept
utilization	O
over	O
the	O
past	O
hour	O
,	O
day	O
,	O
week	O
,	O
month	O
,	O
or	O
year	O
.	O
</s>
<s>
The	O
web	O
front-end	O
shows	O
similar	O
graphs	O
for	O
memory	O
usage	O
,	O
disk	O
usage	O
,	O
network	O
statistics	O
,	O
number	O
of	O
running	O
processes	O
,	O
and	O
all	O
other	O
Ganglia	B-Language
metrics	O
.	O
</s>
<s>
The	O
web	O
front-end	O
depends	O
on	O
the	O
existence	O
of	O
the	O
gmetad	O
which	O
provides	O
it	O
with	O
data	O
from	O
several	O
Ganglia	B-Language
sources	O
.	O
</s>
<s>
Specifically	O
,	O
the	O
web	O
front-end	O
will	O
open	O
the	O
local	O
port	O
8651	O
(	O
by	O
default	O
)	O
and	O
expects	O
to	O
receive	O
a	O
Ganglia	B-Language
XML	B-Protocol
tree	O
.	O
</s>
<s>
The	O
web	O
pages	O
themselves	O
are	O
highly	O
dynamic	O
;	O
any	O
change	O
to	O
the	O
Ganglia	B-Language
data	O
appears	O
immediately	O
on	O
the	O
site	O
.	O
</s>
<s>
This	O
behavior	O
leads	O
to	O
a	O
very	O
responsive	O
site	O
,	O
but	O
requires	O
that	O
the	O
full	O
XML	B-Protocol
tree	O
be	O
parsed	O
on	O
every	O
page	O
access	O
.	O
</s>
<s>
Therefore	O
,	O
the	O
Ganglia	B-Language
web	O
front-end	O
should	O
run	O
on	O
a	O
fairly	O
powerful	O
,	O
dedicated	O
machine	O
if	O
it	O
presents	O
a	O
large	O
amount	O
of	O
data	O
.	O
</s>
<s>
The	O
Ganglia	B-Language
web	O
front-end	O
is	O
written	O
in	O
PHP	B-Application
,	O
and	O
uses	O
graphs	O
generated	O
by	O
gmetad	O
to	O
display	O
history	O
information	O
.	O
</s>
<s>
It	O
has	O
been	O
tested	O
on	O
many	O
flavours	O
of	O
Unix	B-Application
(	O
primarily	O
Linux	B-Application
)	O
with	O
the	O
Apache	B-Application
webserver	I-Application
and	O
the	O
PHP5	O
module	O
.	O
</s>
